Speaking to submission 108 My name is Ian Arthur …...Manawatu River investigations 2013 River Lake...

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Speaking to submission 108

My name is Ian Arthur McIntosh. I am a retired secondary school teacher. I have taught Biology and Science to senior levels for 40 years and Agriculture for 12 years prior to 1985. For about 10 years I also supervised the Napier Boys’ High School farmlet as part of my duties as Head of Agriculture and Horticulture.

1. My interest in this matter was first aroused by the claims of

some HBRC councillors and senior staff that Plan Change 6

had the aim of “improving the quality” of the Tukituki River. I

did not understand how doubling the permitted level of

pollution by faecal matter (as measured by E. coli levels)

could possibly have that effect.1,2

2. I still cannot see how the value ranges proposed in PC63 can

possibly result in “higher quality”. It seems obvious to me that

the only quality issue the changes in PC6 address is that of

visual quality by perhaps reducing the mats of algae

(excepting Phormidium), while permitting the increase in

dissolved nutrients as a result of more intensive land use, to

be as high as possible without triggering the intervention of

the HB District Health Board. That seems to conflict with

Objective TT1(a), (b), (e) and Objective TT2 of Plan Change

6 as updated 26th November. (I am aware that updating PC6

appears to be a continuing process, but submitters can only

comment on the version they have access to.)

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3. The method of periphyton and cyanobacteria control

proposed by the HBRC Resource Management Group4 is

viewed by other scientists as being a high risk strategy. It is

far too simplistic, as has been shown by the recently

documented failure of a similar strategy, as applied to the

Palmerston North Wastewater Treatment Plant, and

periphyton levels in the Manawatu River being above

consented levels.5,6

4. Dr Hickey’s use of the “No Observable Effect Concentration”,

(NOEC) for aquatic organisms is based on a statistical

procedure.7 He reports serious effects on growth and

development of some aquatic species at the NOEC value8,

for which he has adopted the neutral term “Grading” value. I

believe that the level of nitrate pollution he terms

“acceptable” is set too high because of the admitted effects

on growth and development of species such as inanga,9 at

NOEC values.(see his graph)

5. There is considerable disagreement about the TRIM

modelling validity and accuracy. Other submitters have

commented on this, and OVERSEER, in detail and I support

their concerns. I consider that it is misleading to report

‘modelling’ results unaccompanied by a calculated variance

range.

6. The mitigation measures proposed to control high nitrogen

inputs and leaching of dissolved Nitrogen are acknowledged

by the applicants’ experts to be expensive and given the past

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history and desire of the HBRC to avoid overbearing

regulation, are unlikely to implemented widely, or in a timely

manner, on the Ruataniwha Plains. The level of

‘encouragement’ and associated costs of subsidies to

landowners for fencing, planting, etc, for ratepayers or

HBRIC has not been openly stated in any of the applicants’

evidence on PC6 that I have seen.

7. There are already areas of high nitrogen levels in the

groundwater which may impact on human health10. The fact

that several HBRC reports fail to mention the Papanui

Stream, its links to the underlying aquifer or its use as an

outflow channel for the Otane wastewater plant, indicates the

‘science’ of irrigation zone M is poorly understood, despite

the HBRIC stated intention to use the Papanui stream as a

distribution channel for irrigation water11.

8. The Papanui Catchment serves as an example of the

outcomes attending lax management. The farm drain shows

periods of ‘no flow’ in summer12. The flow from the Otane

wastewater treatment plant must be absorbed by the soil or

underlying aquifer during these ‘no flow’ periods, raising

issues of aquifer contamination, particularly considering the

level of contaminants shown in the tables attached to my

submission.

9. None of the evidence presented by the applicant or other

submitters mentions testing/mitigation for Endocrine

Disrupting Chemicals in wastewater. These chemicals are

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well known to interfere with the growth and development of

freshwater species.13

10. As far as Plan Change 6 is concerned, I do not think

that the proposed changes will meet the aims/principles of

the present RMA, HBRMP or NPSFM (2011), i.e.” to

maintain or enhance” the quality of the environment. My

recommendation is that the Board of Inquiry set lower limits

on faecal contamination (eg. A maximum of 260cfu/100mL

similar to the existing RMP) and specify actions that should

be taken when those limits are exceeded. In general I

support the submissions of HB Fish and Game and EDS in

regard to the dissolved Nitrogen levels.

11. In regard to the RWSS, my understanding is that of the

90million cubic metres of stored water, about 50million m3 is

allocated to irrigation and around 40million m3 to “ecological

use” including maintaining minimum flows, and flushing

flows. I have seen no indication as to whether HBRC will pay

the same costs and under the same conditions for

“ecological use” as irrigation water users.

12. The ecological effects of the RWSS are acknowledged

by the Applicant’s experts as including increased nitrate and

phosphate levels in runoff, and disturbance of stream and

river beds by flushing flows. Release of phosphorus from

river/stream sediments and eroded soil particles, as well as

seepage from aquifers to surface waters makes control of

dissolved phosphorus levels a difficult exercise. Again I refer

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the Board to the recent failures of the Palmerston North

Wastewater Treatment Plant .

13. There is insufficient evidence to allow a meaningful

cost/benefit evaluation of the RWSS proposal, but I believe it

will prove to be financially unsustainable without

considerable subsidies from Ratepayers and Taxpayers. I

fully support the conclusion reached by Mr Bostock in that

matter.

Ian A. McIntosh

References

1. Hawkes Bay Regional Resource Management Plan: Vol 1: Chapter 5:

table 8, page 97

2. Exhibit RvV R1 Change 6 – Rebuttal version: section 5.9.1 Fresh

Water Objectives: Table 5.9.1A, page 9 (note Papanui Stream in

Water Management Zone 5 here)

3. Exhibit RvV R1 Change 6 – Rebuttal version: section 5.9.1, Tables

5.9.1A page 9 and 5.9.1B page 10

4. “Tukituki River catchment. Managing Nuisance Growth using Nutrient

Limits.” HBRC Resource Management group, January 2013

5. “Effects of Palmerston North City’s Wastewater Treatment Plant

discharge on water quality and aquatic life the Manawatu River”:

K.Hamill, Opus International, sept 2012

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6. “Processes driving periphyton growth in the Manawatu River and

implications for wastewater treatment”: K.Hamill, River Lake Ltd, sept

2013

7. Hickey EIC page 16 paragraph 7.8

NIWA “Updating nitrate toxicity effects on freshwater species” Hickey,

Jan 2013, page 9.

8. Hickey EIC page 15 paragraph 7.6 for Lake Trout

9. Hickey EIC page 13 paragraph 6.6, page 34 (graph)

10. H.Baalousha, Second Statement of Rebuttal: page 20

11. RWSS “Zone M Primary Distribution Concept” May 2013

12. S.J.Thrush EIC page 4 paragraph 5.1.1

S.J.Thrush BOI Transcript page 1556 paragraph 5.

I.A. McIntosh ‘evidence’ OIR-!3 -C42 Farm Drain samples sep08 to

jul13

13. “State of the Science of Endocrine Disrupting Chemicals – 2012”

WHO, UNEP, IOMC

Processes driving periphyton growth in the Manawatu River and implications for wastewater treatment Prepared for:

Palmerston North City Council

River Lake Ltd

© River Lake Ltd 2013

River Lake Ltd

Processes driving periphyton growth in the Manawatu River and implications for wastewater treatment

Prepared by:

K. D. Hamill (River Lake Ltd)

Prepared for:

Palmerston North City Council

Released by: ………………………………

Keith Hamill

Date: 11 September 2013

Status: Final

Reference: wk-1003

All rights reserved. This publication may not be reproduced or copied in any form without the permission of the client. Such permission is to be given only in accordance with the terms of the client's contract with River Lake Ltd.

River Lake Ltd

PO Box 853, Whakatane 3158,

New Zealand

Telephone: +64 7 929 5293

Mobile: +64 27 308 7224

Email: [email protected]

Manawatu River investigations 2013

19 August 2013 i

Contents

Acknowledgements ................................................................................................................................ 1

Executive summary ................................................................................................................................ 2

1 Introduction ................................................................................................................................. 5

1.1 Background ................................................................................................................................... 5

1.2 Major findings from joint monitoring programme ....................................................................... 5

1.3 Overview of 2013 investigations ................................................................................................... 6

1.4 Statistical analysis ......................................................................................................................... 7

2 Manawatu River water quality and periphyton monitoring 2012/13 .............................................. 9

2.1 Introduction .................................................................................................................................. 9

2.2 Method ......................................................................................................................................... 9

2.3 Results and discussion ................................................................................................................ 12

2.4 Summary ..................................................................................................................................... 24

3 Periphyton accrual rates over time on concrete tiles.................................................................... 26

3.1 Introduction ................................................................................................................................ 26

3.2 Method ....................................................................................................................................... 26


3.4 Summary ..................................................................................................................................... 39

4 Nutrient limitation ...................................................................................................................... 41

4.1 Introduction ................................................................................................................................ 41

4.2 Method ....................................................................................................................................... 41


4.4 Summary ..................................................................................................................................... 52

5 Supply of dissolved phosphorus from river sediments ................................................................. 54

5.1 Introduction ................................................................................................................................ 54

5.2 Methods ...................................................................................................................................... 54


5.4 Summary ..................................................................................................................................... 68

6 Change in dissolved phosphorus fraction due to storage and mixing of effluent with river water .. 70

6.1 Introduction ................................................................................................................................ 70

6.2 Method ....................................................................................................................................... 70


6.4 Summary ..................................................................................................................................... 78

7 Synthesis and Conclusions .......................................................................................................... 79

Manawatu River investigations 2013

19 August 2013 ii

7.1 Impact of the wastewater discharge .......................................................................................... 79

7.2 Reasons why periphyton grows fast downstream of the discharge ........................................... 79

7.3 Implications for the WWTP discharge ........................................................................................ 81

7.4 Complex river dynamics .............................................................................................................. 81

7.5 Further investigations ................................................................................................................. 82

References ........................................................................................................................................... 83

Appendix 1: Water quality results for summer 2012/2013 ..................................................................... 86

Appendix 2: Periphyton growth on artificial substrate upstream (u/s) and downstream (d/s) of WWTP . 89

Appendix 3: Nutrient diffusing substrate results (18 March 2013) .......................................................... 91

Appendix 4: Sediment trapped within periphyton mat .......................................................................... 93

Appendix 6: Photos from artificial substrates Trial A, B and D. ............................................................... 94

Manawatu River investigations 2013 River Lake Ltd

11 September 2013 1

Acknowledgements

A number of people have contributed to support the investigations and improve this report. In particular

thanks to:

Logan Brown from Horizons Regional Council for assisting with much of the fieldwork and review

comments.

Central Environmental Laboratories for undertaking chemical analysis and assisting with sample

collection.

John Quinn (NIWA) for lending piezometer for sampling pore-water from river gravels.

Phil Walker and Rob Green from Palmerston North City Council for managing the project.

John Quinn (NIWA) and Cathy Kilroy (NIWA) for peer reviewing this document and providing

constructive comments.

John McIntosh for document review.


11 September 2013 2

Executive summary

Palmerston North City Council (PNCC) has consent to discharge treated wastewater to the Manawatu River

from the Totara Road wastewater treatment plant (WWTP). Consent compliance monitoring in 2011 found

significantly more periphyton at sites downstream of the discharge and a decline in the quantitative

macroinvertebrate community index (QMCI). This led to concerns that the discharge may be in breach of

condition 3 in its consent to not cause “significant adverse effects on aquatic life”. A joint monitoring

programme was undertaken in 2011/12 to identify the magnitude and causes of the effects from the

discharge; it identified substantially more periphyton growth downstream of the discharge and identified a

number of issues to better understand how this could be addressed. This report discusses the results of

further investigations undertaken in 2012/13 to better understand river processes causing periphyton

growth and the implications for discharges to the river.

Monitoring and investigations were undertaken in the river from November 2012 to April 2013. This

included:

Regular sampling of water quality and periphyton biomass in the Manawatu River;

Using concrete substrates to measure the rate of periphyton growth at different times during the

summer.

Installing periphyton nutrient bioassay to identify which nutrient was limiting periphyton growth;

Experiments to determine the potential for river sediments deposited on and trapped within

periphyton mats to supply dissolved phosphorus to support periphyton growth;

Experiments to assess potential changes in the dissolved phosphorus fraction of the effluent due to

mixing with high pH river water and due to storage.

During periods of low flow (less than half median river flow) the wastewater treatment plant uses an alum

treatment to reduce the amount of dissolved phosphorus (P) in the discharge to a very low concentration

which helps control periphyton growth. However despite the treatment, periphyton grows prolifically

downstream of the discharge. The investigations identified several reasons explaining rapid periphyton

growth downstream of the discharge, these were:

A portion of the particulate P in the discharge is released as dissolved phosphorus after mixing with

the river under certain low flow conditions (i.e. low river flows, large pH fluctuations).

Some of the particulate P associated with suspended solids in the river is trapped within periphyton

mats and releases P directly to growing cells. An increase in pH was able to release some dissolved

P at both the upstream and downstream sites.

Some of the particulate P associated with suspended solids from the discharge is trapped within

periphyton mats and releases P directly to growing cells. Increases in pH were more effective at

releasing dissolved P from trapped sediments (from the river + discharge) at the downstream site

compared to the sediment trapped (from the river only) by periphyton at the upstream site.


11 September 2013 3

These processes for releasing dissolved P were controlled by pH within the river water and periphyton

mats. Daily increases in pH are caused by the periphyton itself, and thus the effect of these processes was

most apparent during periods of low river flow and when periphyton biomass was high. The potential

supply of P increases as periphyton grows because more inorganic sediment is trapped in periphyton mats

as periphyton biomass increases.

Under conditions of very low river flow (e.g. < 20-30 m3/s) background concentrations of dissolved

inorganic nitrogen (SIN) in the Manawatu River were very low and nitrogen became the key nutrient

limiting periphyton growth in the river upstream of the discharge. Furthermore, as the flow continued to

drop below 20 m3/s, the dissolved P in the river increased – further reducing the ability for P to limit

periphyton growth. This may reflect the combined effects of P released from river sediment trapped within

the periphyton mat and a mature periphyton community with less net growth, more senescence and less

net demand for nutrients.

These findings have significant implications for how to best treat the wastewater that is discharged into the

river. Effluent treatment approaches that could be taken to help limit excessive periphyton growth include:

Reducing the dissolved phosphorus concentration (as is currently done at <37 m3/s);

Reducing particulate phosphorus (P) concentration in the discharge in conjunction with the

dissolved P treatment; and

Reducing soluble inorganic nitrogen (SIN) concentration when river flow is very low (i.e. < 20-30

m3/s).

Rivers are complex and it is possible that periphyton will still grow more quickly downstream of the WWTP

discharge compared to upstream even if these actions are taken. However the rate of growth and the

period of time guidelines values are exceeded would be expected to reduce.

We found the complex dynamics occurring in the Manawatu River which emphasises the need for site

specific information when establishing resource consent conditions. In particular:

Estimates of periphyton biomass downstream of the WWTP discharge differed depending on the

method used. Chlorophyll a often over-estimate periphyton biomass at the downstream sites and

AFDM over-estimated periphyton biomass at the upstream site. For sites downstream of the

discharge, AFDM is a better measure for assessing periphyton cover against guideline values

because the AFDM guideline value of 35 mg /m2 corresponds to a decline in mayfly abundance in

the river (as reported in Hamill 2012). Percent cover (e.g. weighted composite cover) provides

complementary information that helps confirm biomass measures.

There was evidence that some characteristics of the sewage stimulated periphyton growth in

addition to the N and P. However the effect was small compared to the combined effect of N and P

stimulating periphyton growth and of little practical consequence.

Grazing by macroinvertebrates played an important role in controlling periphyton biomass at the

upstream site.


11 September 2013 4

Measurement of dissolved reactive phosphorus differed depending on how long samples were

stored prior to analysis. Filtering the samples in the field would ensure more accurate and

consistent results. However it is acknowledged that field filtering is not always practical; where field

filtering of effluent samples do not occur the samples should be transported and filtered in the

laboratory as soon as possible after sampling.


11 September 2013 5

1 Introduction

1.1 Background

In 2008 the Totara Road Wastewater Treatment Plant (WWTP), Palmerston North, was upgraded to

remove phosphorus by alum dosing. This upgrade reduced the phosphorus load entering the

Manawatu River with the discharge and was anticipated to reduce the amount of periphyton

downstream and reduce the consequent impact on the aquatic macroinvertebrate community.

At the time of granting the consent it was predicted that the upgrade would result in a partial

improvement and that in-stream periphyton guidelines would still be exceeded downstream of the

discharge after 18 to 19 days of growth (respective values from Cameron 2002, Biggs and Kelly 2002).

In January 2011 a survey was undertaken by Palmerston North City Council (PNCC) of benthic ecology in

the Manawatu River upstream and downstream of the Totara Road Wastewater Treatment Plant

(WWTP) (Cameron 2011). This survey found that despite a reduction in phosphorus concentrations in

the discharge since the 2008 upgrade, periphyton cover at sites between 800m to 1400m downstream

of the WWTP could still reach high levels. During a period of low flow the site downstream of the

WWTP had a statistically significant elevation of periphyton cover and a corresponding decline in the

quality of the aquatic macroinvertebrate community (as indicated by the SQMCI) compared to

upstream sites.

Horizons Regional Council expressed concern about the reported decline in the SQMCI beyond the 20%

target in the Proposed One Plan, and concern that this might have constituted a breach of Condition 3 f

of the discharge permit (number 101829) which states that:

“3. The discharge shall not:

f. cause significant adverse effects on aquatic life”.

After a series of discussions between PNCC and Horizons it was agreed to develop of a joint programme

of work to further investigate the issue. The results of the 2012 joint monitoring programme are

reported in Hamill (2012).

This report builds on that of the joint monitoring programme (Hamill 2012) and discusses the results of

further investigations undertaken in 2012/13 to better understand river processes causing periphyton

growth. The results are intended to inform decision makers on how to reduce the current effects of the

discharge on the Manawatu River.

1.2 Major findings from joint monitoring programme

The joint monitoring programme (Hamill 2012) identified (among other things) that:

The WWTP discharge stimulated periphyton growth and at high periphyton biomass there was

a change in the composition of the aquatic macroinvertebrate community characterised by a

decline in the abundance of mayfly. It was estimated that such a change in invertebrate

community composition (indicating a decline in habitat quality) would occur on average 1.2


11 September 2013 6

times per summer downstream of the discharge (corresponding to a duration of about 43 days

per summer).

Both nitrogen (N) and phosphorus (P) were identified as potentially limiting periphyton growth

in the Manawatu River at different times; nutrient limitation experiments during April 2012

were inconclusive although P was found to exert some limitation.

The dissolved reactive phosphorus (DRP) from the discharge was not sufficient to explain either

DRP measured in the river or the rate of periphyton growth.

A number of questions were raised by the joint monitoring programme to further improve our

understanding of the processes occurring in the Manawatu River and what aspects of the WWTP

discharge should be improved. Additional monitoring and investigations were undertaken during the

summer of 2012/13 in order to address these questions.

1.3 Overview of 2013 investigations

The following monitoring and investigations were undertaken in 2013:

A trial of extending the flows at which the effluent was alum dosed of to reduced DRP.

Manawatu river water quality and periphyton monitoring to provide background data and

assess impact of trailing alum dosing for a longer period of time;

Calculation of periphyton growth rates progressively during the summer to assess the benefits

of increasing the period of time for which P is removed from the effluent;

Periphyton bioassay to test limitation due to nitrogen, phosphorus and other factors in the

discharge;

Investigating the supply of dissolved phosphorus from river sediments;

Measurement of changes in the dissolved phosphorus fraction of the effluent due to storage

and mixing with river water.

The data collection and field surveys of the river were supported by Horizons Regional Council field

staff and was integrated with other monitoring of the Manawatu River occurring during the summer.

Monitoring of river water quality and periphyton was undertaken by Horizons RC and the data shared.

The summer of 2012/13 contrasted with that of 2011/12 and together they covered a range of river

conditions. The summer of 2011/12 was wet with frequent floods, and many investigations were not

possible until April; in contrast 2012/13 was very dry with long periods of periphyton accrual and

record low flows.

Floods exert a major controlling influence over periphyton biomass and water quality (Biggs 2000) and

results need to be interpreted in the context of river flow. All investigations were undertaken during a

period of low river flows. In relation to the 2013 investigations, the most recent flood of magnitude

over three times median flow was on 15 October 2012 and the largest flood during the monitoring


11 September 2013 7

period was about two times median flow (145 m3/s daily average) on 31 December 2012. A summary of

when the different monitoring occurred with respect to flow during 2012/13 is shown in Figure 1.1

A Weight of Evidence (WOE) approach was used to draw conclusions and management implications

from the various datasets and investigations. A weight of evidence approach combines the analysis of

data (to determine patterns) and experimental hypothesis testing (to determine controlling

mechanisms) to make management recommendations and predictions about their effectiveness.

Figure 1.1: Timing of sampling in relation to flow in the Manawatu River (at Teachers College). The

dashed red line indicates flows of 37 m3/s (half median flow) below which the WWTP must be treating

for phosphorus. Data are 24-hour averages of hourly measurements.

1.4 Statistical analysis

The statistical significance of results was usually determined using an equivalence test in the software

‘TimeTrends’. Equivalence tests incorporate both testing of means (using a student t-test) and testing

of a meaningful change (i.e. interval testing of ‘equivalence’ and ‘inequivalence’). Equivalence tests are

less sensitive to sample size than relying solely on parametric statistics. Increasing the sampling effort

does not affect the likelihood that an equivalence hypothesis will be rejected, unlike parametric tests

comparing mean values, where more data makes it more likely that the null hypothesis will be rejected.

0

10

20

30

40

50

60

70

80

90

100

110

Flo

w (

m3 /

s)

Flow (l/s)

WQ samples

Periphyton

Periphyton Trial A

Periphyton Trial B

Periphyton Trial D

NDS 1

NDS 2


11 September 2013 8

Unless otherwise stated the equivalence tests were based on an interval of +/- 10% and a difference

was only considered statistically significant if the p-value was < 0.05. The potential conclusions resulting

from equivalence test analysis are shown in Table 1.1.

Table 1.1: Most common conclusions resulting from equivalent test analysis using TimeTrends

software.

Conclusion of equivalence tests Null H0: no difference

Equivalence He: within limits

Inequivalence Hi: outside limits

Strong evidence of a practically important difference

Reject Reject Accept

Moderate evidence of a practically important difference

Reject Accept Accept

No practically important difference (difference may be trivial compared to the limits)

Reject Accept Reject

Equivalent / No practically important difference Fail to reject Accept Reject

Equivalent / Inconclusive Fail to reject Accept Accept

In graphs where 95 percentile error bars are shown, these were calculated as two times the standard

error (i.e. SE = SD / √ , where SE = standard error, SD = standard deviation and n = the number of

samples).


11 September 2013 9

2 Manawatu River water quality and periphyton monitoring

2012/13

2.1 Introduction

Weekly river water quality sampling was undertaken to provide information to interpret observed

changes in periphyton cover and composition and to allow more accurate calculation of mass loads

during periods of stable river flow.

Weekly monitoring of periphyton cover and biomass was undertaken to improve our understanding of

periphyton temporal dynamics, variability in space and time, how quickly periphyton cover/biomass

increased after floods, and how much periphyton growth occurred before and after the discharge was

treated for P.

2.2 Method

2.2.1 Water quality

Water quality samples were collected weekly by Horizons RC staff from 16 November 2012 to 10 April

2013. Additional samples were collected during February, increasing the sampling frequency to every 1-

4 days. The sites sampled (Figure 2.1) were:

Manawatu River about 1100m upstream of the discharge point on true right opposite

Turitea Stream confluence and downstream of the riffle;

Manawatu River 800m downstream of the discharge point (on true right)

PNCC WWTP discharge after the wetland.

The unfiltered water samples were stored in a cool chilli-bin and sent to Eurofins ELS Laboratories to

test for variables including: total nitrogen (TN), nitrate-nitrite nitrogen (NNN), total ammoniacal

nitrogen (NH4-N), total phosphorus (TP), total dissolved phosphorus (TDP), dissolved reactive

phosphorus (DRP), turbidity, total suspended solids (TSS), E. coli bacteria. Acid soluble aluminium,

dissolved boron, copper, iron, nickel, and zinc were also measured but the results are not reported in

this report.

Laboratory methods and detection limits used for weekly water quality sampling are shown in Table

2.1. Data collected since October 2012 were reported and analysed as raw results. Where data was

used prior to this period, any results that were less than the detection limit was given the value of half

the detection limit prior to analysis.

In-stream field measurements were made for the following parameters in the Manawatu River:

electrical conductivity (EC), dissolved oxygen (DO), pH, and temperature.


11 September 2013 10

Table 2.1: Laboratory method and detection limits for key variables in weekly sampling

Figure 2.1: Location of water quality monitoring sites on the Manawatu River and the WWTP discharge.

The location of the discharge is indicated with a yellow arrow

2.2.2 Periphyton

Horizons Regional Council staff carried out periphyton cover assessments and sample collection for

biomass determination at the same time and at the same sites as river water quality sampling. All sites

were at the upstream side of a gravel beach and had similar conditions in terms of lighting, clarity,

water depth, water velocity. The upstream site had slightly smaller gravels that were less armoured.

pH Dedicated pH meter following APHA 21st Edition Method 4500 H. <0.1

Turbidity Turbidity Meter following APHA 21st Edition Method 2130 B. <0.01 NTU

Infra Red Turbidity Infrared Turbidity Meter following ISO7027:1999 <0.01 FNU

Inorganic Nitrogen By Calculation - NNN plus Ammonia <0.01 g/m³

Nitrate Ion Chromatography following USEPA 300.0 (modified) <0.005 g/m³

Nitrite-Nitrogen Ion Chromatography following USEPA 300.0 (modified) <0.005 g/m³

Ammonia Nitrogen Flow Injection Autoanalyser following APHA 21st Edition Method 4500 NH3 H. <0.01 g/m³

Total Dissolved Phosphorus APHA 21st Edition Method 4500-P G. Persulphate digestion follows APHA 21st Edition 4500-P B. <0.005 g/m³

Total PhosphorusFlow Injection Autoanalyser following APHA 21st Edition Method 4500-P G. Persulphate digestion

follows APHA 21<0.005 g/m³

Dissolved Reactive Phosphorus Flow Injection Autoanalyser following APHA 21st Edition Method 4500-P G. <0.005 g/m³

Total NitrogenFlow Injection Autoanalyser following APHA 21st Edition Method 4500-NO3 I. Persulphate

digestion follows APHA<0.05 g/m³

E. coli APHA 21st Edition,9223B:2005 <1 MPN/100mL



The monitoring involved visual estimates of periphyton cover in runs and collecting a representative

sample for analysis of chlorophyll a as follows:

1. Visual assessments of periphyton cover were made using an underwater viewer following the

protocols outlined in Appendix 2 of “A periphyton monitoring plan for the Manawatu-

Wanganui Region” (Kilroy et al. 2008). Five points were viewed across each of 8 transects

encompassing run habitat and extending across the wadeable width of the river (i.e. to a

maximum depth of about 0.6m). The first transect location was marked to allow sampling at a

similar location each week. The transects were about 5 metres apart.

2. The visual estimates reported percentage cover of the river bed in each view of the following

categories of periphyton:

clean river bed (no algae);

film (typically diatoms) less than 0.3 cm thick;

loose ‘sludge’ (usually brown);

cohesive mats more (usually brown, don’t fall apart when handled) ;

slimy filamentous algae (usually bright green but can be brown or dark coloured);

coarse filamentous algae (usually green or brown);

cyanobacteria mats (a subset of cohesive mats);

bacterial and/or fungal growths (sewage fungus) visible to the naked eye.

3. Quantitative periphyton samples were collected at the same established monitoring sites and

transects as above, using method QM-1b from the Stream Periphyton Monitoring Manual

(Biggs & Kilroy 2000). This involved removing all periphyton from a 5.0 cm diameter area on

the surface of ten (10) rocks collected across a single transect and the samples bulked to

produce a single sample (i.e. a total area sampled of 0.02 m2). Samples were frozen and sent to

NIWA for analysis of chlorophyll a. Analysis of periphyton samples followed the Biggs & Kilroy

(2000) guidelines for chlorophyll a analysis.

4. Substrate type was assessed visually over the reach when periphyton biomass samples were

collected.

Periphyton visual assessments were used to determine weighted composite cover (Peri WCC) was

calculated as per Matheson et al. (2012) using the formula: Peri WCC = % cover filamentous periphyton

+ (% cover mats/2). Note that this calculation did not include the loose sludge.



2.3 Results and discussion

2.3.1 River water quality monitoring

The weekly sampling results from river water quality and periphyton monitoring are presented in

Appendix 1. For the purpose of statistical analysis this data was filtered to isolate low flow periods (e.g.

half median flow).

During the summer low flow pH, turbidity, electrical conductivity and E. coli bacteria did not differ

between sites upstream and downstream of the WWTP discharge (see Table 2.1 and Table 2.2). In

contrast, the concentration of nutrients (N and P) in the river were significantly higher downstream of

the WWTP discharge (see Table 2.1 and 2.2).

The low flow concentration of total phosphorus was about 80% higher downstream of the discharge

(Table 2.2 and Figure 2.2) and this differential was reasonably consistent throughout the summer (see

Figure 2.4). The concentration of DRP was about 60% higher downstream (Table 2.2 and Figure 2.2)

and on average was above the One Plan target to control periphyton growth both upstream and

downstream of the discharge. The river DRP concentration varied considerably during the summer and

dropped to very low concentrations during January, over which time the DRP measured at the

downstream site was equal to or less than the upstream site (see Figure 2.5). The rise in upstream DRP

as the summer progressed is consistent with the release of DRP from senescence of mature periphyton

and perhaps some influence of periphyton deriving dissolved phosphorus from river sediments as

discussed later in this report.

The discharge contributed a lot of nitrogen to the river, with total nitrogen (TN) about 380% higher

downstream and soluble inorganic nitrogen (SIN) about 2 times higher downstream of the discharge

(see Table 2.2 and Figure 2.3). On average during the summer SIN was below the One Plan target of

0.44 mg/L upstream of the discharge and above the target downstream (see Figure 2.6).

Total ammoniacal N was within ANZECC (2000) water quality guidelines for protection of aquatic life

during the summer (i.e. <0.9 mg/L, see Table 2.1) applicable when sensitive species (e.g. freshwater

mussel or freshwater clam (Sphaerium sp.) are minor components of the invertebrate community. The

concentration of total ammoniacal N in the river downstream of the discharge increased during

February and March as rivers levels dropped to record lows. The maximum recorded total ammoniacal

N concentration during this period was 1.17 g/m3. This is also less than the acute toxicity criterion set

by the USEPA (2009) (i.e. 1.4 g/m3 and 2.4 g/m3 respectively when freshwater mussel are present and

absent), assuming pH 8.5 and temperature of 22oC which were the maximum pH and temperature

recorded during routine monitoring. However, pH in the river late in the afternoon and close to the

periphyton mat was typically higher than that recorded during routine weekly sampling (collected

during the morning). Under these more extreme pH conditions the occasional spikes in total

ammoniacal N during late February would have been close to the USEPA (2009) maximum criterion

(e.g. 1.2 g/m3 at pH 8.9 and 22oC when freshwater mussel absent).

2.3.2 Phosphorus loads

A mass balance approach shows that the phosphorus load from the discharge explained the increase of

TP measured downstream of the WWTP. This is demonstrated by comparing the TP load measured in



the Manawatu River downstream of the discharge with the sum of upstream load plus the load from

the discharge on each sample occasion (i.e. the theoretical downstream load). The measured and

calculated TP loads are similar (see Figure 2.11) which was consistent with results from 2012 (Hamill

2012). Measured TP was expected to be slightly higher than the calculated load since the sample site

(800m downstream) is still within the mixing zone (see Rutherford et al. 1997, Hamill 2012)1. However,

on most occasions it appeared to be slightly less than calculated values. The difference is greater for

particulate P 2 and may indicate deposition or dissolving of some particulate P attached to alum floc

(Figure 2.11) (also see discussion in Section 5).

Unlike the TP load, DRP in the WWTP discharge does not fully explain the increase of DRP measured

downstream compared to upstream. Figure 2.11 shows that measured DRP downstream of the

discharge was generally higher than could be explained by the discharge itself during early summer

(Nov-mid December) and late summer (i.e. from early February), but less than could be explained by

discharge during January. The lower values in January may be the result of periphyton uptake, while the

high DRP values in February may reflect in river processes converting some of the alum bound

particulate phosphorus into dissolved phosphorus, as discussed in Section 5 of this report. Modelling by

MWH found the effect of pH on dissolving some of the particulate P fraction in the discharge was most

apparent at low flows experienced in February and March (MWH 2013).

Table 2.1: Median values of key water quality variables in the Manawatu River and WWTP discharge

when river flow was less than median flow (<73 m3/s) (period 1 November 2012 to 10 April 2013)

1 However it is beyond the consented mixing zone which is 600m of total ammoniacal nitrogen and 400m for most

other variables. 2 Particulate P was calculated as total phosphorus - total dissolved phosphorus.

Variable pH EC

(uS⁄cm)

DRP

HRC

(g⁄m3)

TDP

(g⁄m3)

Particulate

P (g⁄m3)

TP

(g⁄m3)

TN

(g⁄m3)

SIN

(g⁄m3)

NH4-N

(g⁄m3)

NNN

(g⁄m3)

Turbidity

EPA

(NTU)

E. coli

(MPN⁄100mL)

Chla

(mg⁄m2)

Mawatu u⁄s 7.9 222.0 0.012 0.013 0.0045 0.017 0.186 0.010 0.001 0.008 1.3 30 25

Mawatu d⁄s 7.9 234.3 0.018 0.019 0.011 0.032 0.832 0.630 0.473 0.092 1.3 30 212

PNCC STP

discharage7.3 818.5 0.06 0.096 0.883 0.99 37.037 36.849 36.7 0.103 5.4 25



Table 2.2: Statistical comparison of variables in the Manawatu River upstream and downstream of the

WWTP when river flow was less than half median flow (<37 m3/s) (period 1 Nov 12 to 10 April 13).

Refer to Table 1.1 for an explanation of the statistical method.

Figure 2.2: Average concentration of phosphorus fractions in the Manawatu River upstream and

downstream of the WWTP discharge, when river flow was less than half median flow (<37 m3/s) (period

1 November 2012 to 10 April 2013). Error bars are 95 percentiles. The red line = DRP One Plan target.

Manawatu River

u/s vs d/s

equivalence

analysis

t-test

p -value

Bayesian posterior

probability that difference

is within limits

mean

upstream

mean

downstream

mean

discharge

pH No difference 0.14 100% 8.0 7.9 7.3

EC Equivalent 0.15 77% 232.3 247.8 811.3

DRP (g⁄m3) Strong evidence 0.003 0.6% 0.0116 0.0182 0.0493

TDP (g⁄m3) Strong evidence 0.0003 0.1% 0.0136 0.0226 0.0975

Particulate P (g⁄m3) Strong evidence 0.0002 <0.1% 0.0040 0.0096 0.88

TP (g⁄m3) Strong evidence <0.0001 <0.1% 0.017 0.031 0.974

TN (g⁄m3) Strong evidence <0.0001 <0.1% 0.195 0.934 38.3

SIN (g⁄m3) Strong evidence <0.0001 <0.1% 0.033 0.677 36.1

NH4-N (g⁄m3) Strong evidence <0.0001 <0.1% 0.003 0.576 36

NNN (g⁄m3) Strong evidence <0.0001 <0.1% 0.030 0.101 0.093

Turbidity (NTU) Equivalent 0.7 43.0% 1.2 1.3 5.1

E. coli (MPN⁄100mL) Equivalent 0.6 3.9% 146.2 277.3 190

Chorophyll a (mg⁄m2) Strong evidence 0.0001 <0.1 47 328

Load DRP (kg/day) Strong evidence 0.0009 0% 12.6 20.3 1.17

Load TP (kg/day) Strong evidence 0.0001 <0.1 21.1 37.1 23.2

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

upstream downstream

Ph

osp

ho

rus

(g/m

3)

TP

TDP

DRP



Figure 2.3: Average concentration of nitrogen fractions in the Manawatu River upstream and

downstream of the WWTP discharge, when river flow was less than half median flow (<37 m3/s) (period

1 November 2012 to 10 April 2013). Error bars are 95 percentiles. The red line = SIN One Plan target.

Figure 2.4: Total phosphorus concentration in the Manawatu River upstream and downstream of the

WWTP discharge. Flow is daily average river flow on day of sampling. Note that spikes correspond with

high river flow.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

upstream downstream

Nit

roge

n (

g/m

3)

TN

SIN

NH4-N

NNN

0

50

100

150

200

250

300

350

400

450

500

0.000

0.020

0.040

0.060

0.080

0.100

Flo

w (

m3/s

)

TP (

g/m

3)

downstream

upstream

Flow



Figure 2.5: Dissolved reactive phosphorus concentration in the Manawatu River upstream and

downstream of the WWTP discharge. Note that during January 2013 downstream DRP was equal to or

less than upstream DRP.

Figure 2.6: Soluble inorganic nitrogen concentration in the Manawatu River upstream and downstream

of the WWTP discharge

0

50

100

150

200

250

300

350

400

450

500

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

Flo

w (

m3/s

)

DR

P (

g/m

3)

downstream

upstream

Flow

0

50

100

150

200

250

300

350

400

450

500

0.00

0.20

0.40

0.60

0.80

1.00

1.20

Flo

w (

m3/s

)

SIN

(g/

m3)

downstream

upstream

Flow



Figure 2.7: Total phosphorus load in the Manawatu River measured downstream of the discharge and a

mass balance calculation of the loads upstream of the WWTP discharge + the discharge. Filtered for

river flows < 37 m3/s.

Figure 2.8: Particulate phosphorus load in the Manawatu River measured downstream of the discharge

and a mass balance calculation of the loads upstream of the WWTP discharge + the discharge. Filtered

for river flows < 37 m3/s. Note that measured particulate P is consistently less than expected,

suggesting that particles were settling out of the water.

0

10

20

30

40

50

60

70

80

90

100TP

load

(kg

/day

)

Measured TP load d/s

Calculated TP load

0

10

20

30

40

50

60

70

80

90

100

Par

ticu

late

P lo

ad (

kg/d

ay)

Measured PP load d/s

Calculated PP load

Flow (m3/s)



Figure 2.9: DRP load to the Manawatu River measured downstream of the discharge and a mass

balance calculation of the loads upstream of the WWTP discharge + the discharge. Filtered for river

flows < 37 m3/s. Note that measured DRP was less than expected during January (corresponding to a

period of rapid periphyton growth and nutrient demand) and more than expected in late summer -

suggesting net release of dissolved P from a mature periphyton community.

2.3.3 Switch of potential nutrient limitation

In order to examine the potential for nutrient limitation of periphyton growth, the concentration of the

dissolved nutrients SIN and DRP were expressed as equivalent periphyton biomass (chlorophyll a) using

the equation in Biggs (2000) and assuming 21 days of accrual3 (see Figure 2.10 and 2.11). This is not a

prediction of the periphyton biomass (which will be affected by other factors such as flood events,

grazing etc.), but allows us to express the river concentrations of SIN and DRP on a common scale

relevant to periphyton growth.

The Manawatu River upstream of the WWTP showed a switch in the potential limiting nutrient from

phosphorus to nitrogen as flow receded (Figure 2.11). Upstream of the WWTP, DRP was potentially

limiting periphyton growth from 1 Nov to mid-Dec 2012 and again in January 2013. Background

concentrations of DRP steadily increased above the median during February – March (Figure 2.5). SIN

concentrations steadily declined over the summer and started exerting a strong control on periphyton

growth from late December, interrupted only by small flood events which briefly elevated SIN.

3 The accrual period is the period of time available for periphyton to grow between floods.

0

5

10

15

20

25

30

35

40

45

DR

P lo

ad (

kg/d

ay)

Measured DRP load d/s

Calculated DRP load

Flow (m3/s)



The gradual decline in SIN probably reflects a combination of reduced external loads (e.g. reduced soil

drainage from the catchment) in addition to periphyton uptake and denitrification within river

sediments (e.g. Partitt et al. 2007).

The changes in DRP probably reflect dynamics of internal river processes such as P uptake by growing

periphyton, release by old periphyton cells and release from river sediments (see Section 5 for further

discussion). McArthur et al. (2010) reported a similar situation of elevated DRP during late summer in

the upper Manawatu; in this case DRP concentration during a low flow period in late March was higher

than the annual median which was considered unexpected considering there are few mechanisms for P

to reach waterways during dry conditions. This points towards an increase in internal P loads during

these low flow conditions such as dissolved P release from sediments and senescence of algal cells.

Downstream of the WWTP the absolute concentration of DRP occasionally dropped to levels potentially

limiting periphyton growth during December and throughout January (i.e. below the red line on Figure

2.11). SIN was continuously high at the downstream site and concentrations increased late in the

summer due to dropping river flows (reducing dilution) and a constant SIN load from the WWTP.

Nutrient concentrations in the water reflect the residual of what is not being used by periphyton and it

is apparent that even the low DRP concentrations during mid-January were not restricting periphyton

growth (see Figure 2.11) – probably because periphyton was deriving P from sediment trapped in its

mat (see Section 5).

In a review of Horizons RC periphyton monitoring data, Kilroy (2012) found that the percentage of

periphyton biomass exceedance of One Plan targets was unrelated to mean DRP at the site, but there

was a threshold response between exceedance and mean SIN concentration. The target guideline was

rarely exceeded when mean SIN concentration was <0.1 g/m3. This pattern suggested that periphyton

biomass in the region may be more generally limited by SIN than by DRP.

The switch from potential P limitation to N limitation generally occurred when river flows were

between 20 m3/s to 30 m3/s. This is illustrated in Figure 2.12 which shows the relationship between

SIN:DRP ratio at the upstream site and river flow after filtering data for SIN<0.3 mg/L4. Provided

absolute concentrations are sufficiently low a SIN:DRP ratio <7.2 indicates potential N limitation. When

flows dropped below 30 m3/s SIN concentrations reduced to <0.1 mg/L so as to allow either N or both N

and P to be potential limiting. When flows were <20 m3/s both the SIN concentration and the SIN:DRP

ratio were low – indicating N as the primary limiting nutrient upstream of the discharge.

This switching from potential P limitation to N limitation at the upstream site as river flow receded has

important implications for managing the WWTP discharge to avoid excessive periphyton growth. In the

early stages of a flow recession P can control periphyton growth. As the flow continues to drop (e.g. to

<30 m3/s) N also becomes important for controlling periphyton growth, and as the flows drop further

(e.g. to <20 m3/s) N remains a controlling nutrient but P becomes less important due to increasing

background concentrations (e.g. as flow fell below 15 m3/s in February 2013).

4 The data was filtered for low concentrations because a nutrient will only be limiting if the absolute concentrations

are low. SIN is likely to become limiting in the range of 0.1 to 0.3 mg/L and DRP in the range 0.01 to 0.03 mg/L (corresponding to 120 to 200 mg/m

2 chlorophyll a after 21 days of accrual (Biggs 2000).



Figure 2.10: Modelled periphyton growth in response to dissolved reactive phosphorus (DRP) and

soluble inorganic nitrogen (SIN) in the Manawatu River upstream of the WWTP discharge. The river is

potentially N limited when the SIN line drops below the DRP line. The red line shows the One Plan

target for periphyton chlorophyll a for this site.

Figure 2.11: Modelled periphyton growth in response to DRP and SIN in the Manawatu River

downstream of the WWTP discharge. The river is potentially P limited when the DRP line is below the

SIN line. The red line shows the One Plan target for periphyton chlorophyll a for this site.

0

50

100

150

200

250

300

350

400M

od

elle

d C

hl a

(m

g/m

2)

afte

r 2

1 d

ays

DRP equivalent

SIN equivalent

River Flow

0

50

100

150

200

250

300

350

400

450

Mo

de

lled

Ch

l a(m

g/m

2)

afte

r 2

1 d

ays

DRPequivalentSINequivalent

Periphyton grew abundantly during January despite low DRP



Figure 2.12: Ratio of SIN:DRP in Manawatu River upstream of the discharge filtered to only show

records where SIN <0.3 mg/L (period March 2010 to April 2013). Values below the shaded blue line

indicate potential nitrogen limitation (based on the Redfield ratio). The Redfield ratio is represented by

a wide band because optimum N:P ratios can differ between species.

2.3.4 River periphyton monitoring

Weekly sampling of periphyton biomass in the Manawatu River found a substantially more biomass in

the river downstream of the discharge compared to upstream (see Table 2.2 and Figure 2.13).

Periphyton biomass at the upstream site initially increased in the one to two weeks after flood events

after which it declined. Substantial grazing by macroinvertebrates was observed on substrates placed in

the river. Therefore declines in biomass at the upstream site would be consistent with removal by

macroinvertebrate grazing exceeding the periphyton growth rate.

The upstream site showed more response in terms of periphyton cover (expressed as Periphyton

weighted composite cover (WCC))5 compared to chlorophyll a (see Figure 2.14). This was particular

evident during January. The decline in cover at the downstream site on 16 January may be due to a

small fresh at the time causing sloughing.

There was spatial variability in periphyton cover at the upstream site. Periphyton cover was sparse in

runs where regular sampling occurred, but the cover was relatively high in riffles (dominated by green

filamentous alga Cladophora sp. and Stigeoclonium sp.). Periphyton (Cladophora sp.) from the riffle

was used for sampling sediment trapped in periphyton mats (see Section 5).

5 Peri WCC = % cover filamentous periphyton + (% cover mats/2) see Matheson et al. (2012).

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

SIN

:DR

P

Flow (m3/s)

SIN<0.1 mg/L

SIN 0.1 - 0.2 mg/L

SIN 0.2 - 0.3 mg/L



Periphyton grew rapidly at the downstream site and attained high biomass in both runs and riffles, this

was despite the DRP concentration in the river being very low during this period – suggesting that the

periphyton had another source of phosphorus.

There was a positive correlation between periphyton biomass (measured as chlorophyll a) and

periphyton weighted composite cover (WCC) (r2 = 0.77 at the downstream site on log log transformed

data) (see Figure 2.15).6 If both periphyton cover and chl a biomass were used to assess compliance

with the One Plan targets (based on Biggs 2000), then the biomass measure expressed as chlorophyll a

would have exceed the target of 120 mg/m2 more frequently than the equivalent 30% cover by

filaments. Matheson et al. (2012) compared periphyton biomass and cover with QMCI and MCI scores

and found that the boundary between ‘good’ and ‘fair’ ecological condition (i.e. MCI=100, QMCI=5)

corresponded to chlorophyll a of about 200 mg/m2 and Peri WCC of 40%. On this basis also the

periphyton at the downstream site in the Manawatu River appears to have more relatively more

chlorophyll a for a given cover and biomass measure using chlorophyll a may be over estimates (see

also Section 3.3).

Kilroy et al. (2012) assessed the extent to which the One Plan target for periphyton biomass (i.e. 120

mg/m2) corresponded to the One Plan target for periphyton cover (i.e. 30% and 60% cover by filaments

and mats respectively). The analysis found that the cover thresholds were equivalent to about 53

mg/m2 chlorophyll a provided the remaining cover had zero chlorophyll a. In practice there will be

algae present in other sections of the stream and the biomass cover is likely to be more. Conversion

factors derived for Canterbury indicated a chlorophyll a equivalent nearer 140 mg/m2 for 30%

filaments. The downstream site appears to have more chlorophyll a for a given percent cover than

typical in other reaches. This may relate to the concentration of chlorophyll a in the cells (see Section

3.3.3).

During the summer of 2012/13 PNCC WWTP trialled increasing the period of time for which DRP is

removed from the effluent, i.e. starting removal at about 60 m3/s river flow. Because of the dry

summer conditions this resulted in the discharge having low DRP in early December (interrupted by

floods from 20 to 30 December) and almost continuously from January to March with the exception of

flood events in 5 Feb and 19th March. These extended periods of alum dosing and low DRP in the

discharge had no observable effect on reducing periphyton biomass in the river downstream.

Periphyton biomass was higher in February and March compared to November and December (see

Figure 2.13) despite the alum treatment having occurred for a longer period of time and very low DRP

concentrations in the effluent (i.e. average DRP concentration in effluent during February March was

0.059 mg/L compared to about 3 mg/L when no alum dosing is occurring).

6 A slightly better correlation was obtained when comparing cover with chlorophyll a + pheophytin, but pheophytin

data was only available since November 2013.



Figure 2.13: Periphyton biomass (measured by chl a) in the Manawatu River upstream and downstream

of the WWTP. Periphyton biomass reduced after small floods as indicated by vertical lines on the graph

(short line <100 m3/s, long line >100 m3/s).

Figure 2.14: Periphyton weighted composite cover (WCC) in the Manawatu River upstream and

downstream of the WWTP. Periphyton biomass reduced after small floods as indicated by vertical lines

on the graph (short line <100 m3/s, long line >100 m3/s).

0

100

200

300

400

500

600

700

800

900

Ch

loro

ph

yll a

(mg/

m2)

downstream

upstream

0

10

20

30

40

50

60

Pe

rip

hyt

on

Wei

ghte

d C

om

po

site

Co

ver

(%) downstream

upstream



Figure 2.15: Correlation between chlorophyll a and periphyton weighted composite cover (WCC) in the

Manawatu River upstream and downstream of the discharge (for summers 2011/12 and 2012/13). The

red lines indicate values corresponding to ‘good’ water quality (from Matheson et al. 2012). An outlier

of 885 mg/m2 chlorophyll a was excluded from the regression.

2.4 Summary

The key messages from this chapter are:

The concentrations of nutrients in the Manawatu River were, on average, higher downstream

of the discharge compared to upstream.

The river DRP concentration varied considerably during the summer and dropped to very low

concentrations during January, over which time the DRP measured at the downstream site was

equal to or less than the upstream site.

DRP concentrations increased during late summer low flows to above the summer median at

both upstream and downstream sites - suggesting the release of DRP from senescence of

mature periphyton and perhaps some influence of periphyton deriving dissolved phosphorus

from river sediments trapped in the periphyton mat.

Downstream of the discharge there were periods when low DRP concentrations could

potentially limit periphyton growth, but SIN continually remained high. During January, when

DRP concentrations were very low, the periphyton downstream of the discharge was growing

R² = 0.63

0

10

20

30

40

50

60

70

80

0 100 200 300 400 500 600

Per

i WC

C (

% c

ove

r)

Chlorophyll a (mg/m2)

Downstream

Upstream

d/s site regression line



rapidly and showed little evidence of nutrient limitation. This also suggests the periphyton was

obtaining phosphorus from other sources (e.g. trapped sediments).

There was less particulate P measured in the river than would be expected due to the discharge

– suggesting settling out of particulate phosphorus.

There was more DRP measured in the river than would be expected due to the discharge in

early summer and late summer – but less DRP during January. This points to the interaction of

different in-river processes such as periphyton uptake of DRP (in January) and net release of

DRP in February, from senescence of mature periphyton and perhaps some influence of

periphyton deriving dissolved phosphorus from river sediments.

In the river upstream of the discharge, the potential limiting nutrient changed during the

summer from potential P limitation to potential N limitation.

The downstream site appeared to have relatively high concentrations of chlorophyll a for a

given percent cover compared to the upstream site and typical values for other rivers.

Long periods of removing DRP from the discharge by alum dosing (e.g. February and March)

had no noticeable effect on downstream periphyton biomass compared to short periods (e.g.

November and December).



3 Periphyton accrual rates over time on concrete tiles

3.1 Introduction

One possibility raised in Hamill (2012) to explain higher than expected dissolved phosphorus (e.g. TDP

and DRP) concentrations in the river and faster than expected downstream periphyton growth was that

river sediments may act as a buffer to store phosphorus when water concentrations are high (e.g. no

alum treatment) and release phosphorus when river concentrations are low (e.g. when alum dosing is

occurring). If this mechanism of phosphorus (P) release was occurring then one management response

could be to start alum dosing at higher flows and for a longer period of time. This would be expected to

reduce the period of time that DRP in the downstream river water could be sorbed by sediments and

thus reduce the amount of P available for release during low flows (if this mechanism is occurring).

During the summer of 2012/13 PNCC WWTP trialled extending the period of time for which DRP was

removed from the effluent. Between 1 November and 30 March the alum dosing was only interrupted

by flood events on 19 November 2012, 6-9 December, 19-20 December, 28 December to 3 January, 5 -7

February and 19-20 March (the average DRP concentration in the effluent during the 1 Dec -31 March

period was <0.1 mg/L 7compared about 3 mg/L when not alum dosing. This presented an opportunity

to test whether doing the current alum dosing for a longer period of time provided any benefit by, for

example, depleting phosphorus that might be stored in river sediments as a result of a concentration

gradient. As discussed in Chapter 2, long periods of removing DRP from the discharge by alum dosing

(e.g. February and March) had no noticeable effect on downstream periphyton biomass compared to

short periods (e.g. November and December).

The hypothesis that extending the period of alum dosing will help reduce periphyton growth (due to

less DRP release from the sediment during low flows) was tested by growing periphyton on artificial

substrates consecutively placed in the river at one to two week intervals. Specific growth rates for the

periphyton (normalised for accrual period and for temperature) were estimated and compared. The

hypothesis would be supported if specific growth rates at the downstream site were slower after river

sediments were exposed to a longer period of low DRP concentrations in the water (i.e. a longer period

of alum dosing).

Comparing estimates of specific growth rates for algae with theoretical maximum growth rates also

tests the extent to which there is any limitation (e.g. by nutrients) on periphyton is growth (see Biggs

1990). For this purpose it is most effective to focus on measurements on the initial and exponential

stages of periphyton growth.

3.2 Method

3.2.1 Sampling method

Periphyton accrual rates were assessed by measuring periphyton biomass growing on replicated

artificial substrates (concrete paving tiles) placed in the river at one to three week intervals. Using

7 Flow weighted composite sample.



artificial substrates reduces the influence of substrate type and armouring on periphyton development

at different sites.

Ten concrete tiles (190x220mm) were placed in the river at monitoring sites: 800m upstream (true left

bank) and 800m downstream (true right bank).

Three sets (trials) of tiles were placed in the river at one to six week intervals to allow comparison of

different periods of alum treatment on periphyton accrual. The first trial (A) was installed on 10

January after 10 days of alum treatment, and subsequent trials were installed after 10 + 7 (B) and 10 +

14 (C) days of alum treatment (Table 3.1). Periphyton biomass samples were collected from artificial

substrates every three to four days during a flow recession to allow up to 21 days of accrual. Table 3.1

shows the time at which substrates were placed in the river and sampled. Trial A was installed 10 days

after the last flood, which was just under three times median flow.

Trial C was abandoned because of a small flood on 5th February 2013. These tiles were scrubbed clean

of periphyton and used for Trial D, which was started on Friday 8 February. On this date additional tiles

were also placed at three additional sites: 1.2 km downstream, 3.8km downstream (u/s Longburn) and

4.7 km downstream (d/s Longburn); replicate samples were collected from these sites on day 21 to

enable a longitudinal comparison of periphyton.

Periphyton biomass was collected from the tiles using method QM-1b from the Stream Periphyton

Monitoring Manual (Biggs & Kilroy 2000). Specifically this involved removing all periphyton from a 5.0

cm diameter area on the surface of ten (10) artificial substrates (one sample per concrete tile) and

bulked (i.e. a total area sampled of 0.02 m2). In order to allow a robust comparison of periphyton

biomass between sites, replicate samples were collected on day 21 for Trial A and D. Instead of bulking

all the samples, paired samples were bulked to produce five replicate samples from ten 5.0 cm

diameter sample areas on the tiles (i.e. sampling 0.004 m2 per replicate). Samples were frozen and sent

to NIWA for analysis of chlorophyll a and Ash Free Dry Mass (AFDM) 8. Analysis of periphyton samples

followed the Biggs & Kilroy (2000) guidelines for AFDM and chlorophyll a analysis using ethanol

extraction.

Chlorophyll a and AFDM provide complementary information on periphyton biomass. Chlorophyll a

gives an indication of autotrophic organisms. AFDM is a measure of the total organic material in the

sample and includes autotrophic and heterotrophic microorganisms, plus dead periphyton and detritus.

Water depth and velocity were recorded using the ruler method (see Harding et al 2009) above each

tile (see Appendix 2).

Table 3.1: Timing of sampling from artificial substrates. Tiles were sampled every 3-4 days as

recommended in Biggs and Kilroy (2000).

Date Days since alum dosing

Lag since starting P treatment

Trial A (10 Jan)

Trial B (17 Jan)

Trial C (24 Jan)

Trial D (8 Feb)

10 Jan 7 installed

17 Jan 14 X 7 installed

8 AFDM is also sometimes referred to as Ash Free Dry Weight (AFDW).



21 Jan 18 X 11 installed

24 Jan 21 X 14 X 7

28 Jan 18 X 18 X 11 X 7

31 Jan 21 X 21 (replicates)

X 14 X 11

4 Feb 25 X 18 X 14

170 m3/s flood on 5

th Feb (no alum dosing on 6-7 Feb)

8 Feb 1 installed

12 Feb 5

15 Feb 8 X 7

19 Feb 12 X 11

23 Feb 16 X 15

26 Feb 19 X 18

1 Mar 22 X 21 (replicates)

5 Mar 26 X 25

3.2.2 Net biomass accrual rate

The net rate of biomass accrual was calculated using the method in Biggs and Kilroy (2000). This

method provides an estimate of periphyton growth rates in situations where loss due to invertebrate

grazing and detachment are low.

The net accrual rate was calculated by regression using the equation:

B = a exp(kT)

Where:

B is the biomass measure per square metre at day T,

a is the initial biomass concentration at T=0, and

k is the net accrual rate during the exponential growth phase.

The net accrual rate (k) was calculated by loge transforming the biomass data, plotting this against days

accrual and calculating the slope of exponential phase of growth. A k value of < 0.1 /day is considered

low and a k value of >0.35/day is considered high (Biggs and Kilroy 2000).

To reduce the effect of algal settlement rate on calculating growth rates the first seven days was

omitted from the calculation unless otherwise stated (as per approach in Biggs 1990)

3.2.3 Specific growth rate

Specific growth rate (µ) was calculated by using the net accrual rate (k) and applying a correction to

convert the value to log2: μ = k/0.693. This equates to the number of cell divisions per day (Bothwell

1988).

The relative growth rate was calculated as: μ/ μmax



Where μmax is the maximum specific growth rate for nutrient saturated algae.

The maximum specific growth rate (μmax) was calculated using the model in Bothwell (1988) (based on P

limiting conditions):

μmax = 0.189 +0.0278 t

where: t = temperature in degrees Celsius9.

The relative growth rate adjusts for the effects of temperature on algae growth and thus isolates algae

growth as a function of the limiting nutrient concentration. A low relative growth rate μ: μmax of <0.3

indicates growth is limited by low nutrient (P) concentrations; 0.3-0.8 indicates slight nutrient

deficiency, and a high relative growth rate μ: μmax of >0.8 indicates that growth is not limited by

nutrients (i.e. nutrients are replete) (Bothwell 1985, Biggs 1990).

These specific growth rate estimates assumed that losses from emigration, death and invertebrate

grazing are minimal. This was not the case at the upstream site where there was evidence of

considerable grazing from macroinvertebrates. Thus estimates for biomass accrual and specific growth

rate at the upstream site were based on the maximum accrual rate measured between any sample

dates and are considered minimum estimates.

In order to calculate specific growth rate from AFDM measurements the data was first converted into

equivalent chlorophyll a values using the following formula from Biggs (2000):

Ln Chlorophyll a (mg/m2) = 0.338 + 1.396 x Ln AFDM (g/m2).

3.2.4 Autotrophic Index (AI)

The autotrophic index (AI) was calculated on sample results to indicate the extent of heterotrophic

growth within the periphyton community. AI is the ratio of ash-free dry mass (AFDM) to chlorophyll a.

For in-stream periphyton communities unaffected by organic pollution, the AI ratio is normally between

100 and 200 (but the range can be from 50-250 and vary as a function of nutrient availability, light

intensity and age of cells (McIntire and Phinney (1965))10. AI values greater than 400 are taken to be

indicative of communities affected by organic pollution (Biggs and Kilroy 2000). AI is not accurate when

the periphyton biomass is low i.e. < 2 g/m2.

9 Average of hourly monitoring data from Manawatu at Teaches College where available. An average temperature of

20.8oC and 21.1

oC applied to trial A and B, and trial D respectively.

10 Biggs (2000) provides regression equations to convert between AFDM and chlorophyll a. These are: Ln Chlorophyll a

(mg/m2) = 0.338 + 1.396 x Ln AFDM (g/m

2); and Ln AFDM (g/m

2) = 0.186 + 0.566 x Ln chlorophyll a (mg/m

2).

Equivalent values for AFDM and Chl a in the periphyton guidelines (35 g/m2 and 200 mg/m

2 respectively) imply a

typical AI of 175.




3.3.1 Periphyton accrual and growth rate

The results of periphyton biomass measurements from the artificial substrates are shown in Appendix

2. At the downstream sites the growth of periphyton showed a similar pattern on all the trials i.e. an

accrual phase of initial colonisation and exponential growth followed by a loss phase with autogenic

sloughing soon after the initial biomass peak. Trial D was long enough to see this followed again by a

growth phase. The periphyton species composition on the concrete tiles changed over the three-four

weeks of growth; Stigeoclonium sp. rapidly colonised the substrates, followed by cyanobacteria, stalked

diatoms and filamentous algae such as Cladophora species (see Figure 3.1). This succession might be

partially due to macroinvertebrate grazing pressure, for example Cladophora sp. is resistant to

chironomid grazing.

At the downstream site the first biomass peak occurred progressively more quickly for trials later in the

summer. In Trial A the initial peak biomass occurred after 18 days accrual, in Trial B it occurred after

about 14 days accrual, and in Trial D it occurred between <7 to 11 days of accrual depending on which

biomass measure was used (chlorophyll a or AFDM) (Figure 3.2 and 3.3), i.e. the sampling did not fully

capture the first exponential growth phase.

Periphyton AFDM exceeded the 35 g/m2 guideline for protection of trout habitat within 15 to 17 days

(Figure 3.3). The equivalent guidelines in terms of chlorophyll a (i.e. 200 mg/m2) was exceeded

considerably sooner.

Periphyton biomass was supressed at the upstream site; probably due to macroinvertebrate grazing as

chironomids tubes and caddis nets were abundant on the concrete tiles. Upstream results from the

Trial A and B had very little biomass accrual and no exponential growth phase. During Trial D the

upstream site had exponential growth from days 11 to 18. This would be consistent with

macroinvertebrate sampling results National River Water Quality Network (NRWQN) invertebrate data

for Teachers College (WA8) on 1 March 13 that showed moderate numbers of Hydropsyche (formerly

Aoteapsyche) net-spinning caddis (1783/m2) and Tanytarsus and Orthoclad chironomids (1429/m2)

along with moderate numbers of snails (Potomopyrgus 537/m2), Deleatidium mayfly (676/m2) and

Elmid beetle larvae (439/m2) (John Quinn pers. comm. 2013).

Net biomass accrual and specific growth rate was assessed on the period of exponential growth.

Slightly different periods were used for measures of chlorophyll a and AFDM (see Table 3.2). The loge

adjusted AFDW values are shown in Figure 3.4.

Specific growth rates at the downstream site were fastest for Trial D followed by Trial A and Trial B

(Table 3.2). Some of the differences between Trial A and B may be due to peak biomass falling between

sampling intervals. During Trial B chlorophyll a accrued more slowly than AFDM, while in Trial A the

rates of accrual estimated by the different measurements were similar and in Trial D the rate of

chlorophyll a accrual was faster. Some nutrient limitation was suggested by chlorophyll a

measurements of Trial B (i.e. a low relative specific growth rate of 0.24) but this was not supported by

estimates using AFDM – suggesting other factors could have restricted chlorophyll a accrual (e.g.

grazing). Relative specific growth rates from chlorophyll a data suggested that periphyton growth was

nutrient replete during Trial D (i.e. specific growth rates were higher than theoretical maximum growth



rates). However the relative specific growth rates estimated from AFDM were considerably lower and

suggested some limitation on growth (Table 3.2). The difference is partially due to a surprisingly low

chlorophyll a value causing a high ratio of AFDM to chlorophyll a on Day 15 (23 February) (AI=743).

As discussed previously, the upstream site during Trial A and B had low periphyton biomass and very

little growth after day 7 – probably due to grazing. However the burst of periphyton growth during days

15 to 18 of Trial D was very rapid and the growth rate similar (slightly faster even) than the downstream

site over the same period. Biomass reached 198 mg/m2 before rapidly declining again (Figure 3.2, Table

3.2).

Finding nutrient replete growth on upstream tiles, even over a short period of time, is surprising

considering the low concentrations of DRP and particularly SIN in the water. However the short term

increase (rapidly increasing and declining within a week) may reflect a temporal variation in grazing

pressure and rapid recycling of nutrients, or patchiness of chlorophyll a rich species on the tiles. Note

that photographs taken at the time support the data and show a mat of periphyton and patches of

Stigeoclonium sp. on tiles at the upstream site (see Appendix 6).

Figure 3.1: Periphyton succession on a concrete tile in the Manawatu River downstream of the

discharge (7 March 2013, day 27 of Trial D). Sections of the tile were sampled every 3 to 4 days in the

order: top left, bottom left, top right, bottom right, top middle, bottom middle. Stigeoclonium sp

rapidly colonised the substrates, followed by cyanobacteria (right hand side), stalked diatoms and

filamentous algae such as Cladophora species.



Figure 3.2: Periphyton accrual on artificial concrete substrates in the Manawatu River upstream and

downstream of the WWTP discharge. Biomass assessed as chlorophyll a. The dashed red line indicates

the NZ periphyton guideline value for trout habitat. Error bars are two standard errors.

Figure 3.3: Periphyton accrual on artificial concrete substrates in the Manawatu River upstream and

downstream of the WWTP discharge. Biomass assessed as AFDW. The dashed red line indicates the NZ

periphyton guideline value for trout habitat. Error bars are two standard errors.

0

100

200

300

400

500

600

0 5 10 15 20 25

chlo

rop

hyl

l a(m

g/m

2 )

Days accrual

Trial A u/s

Trial A d/s

Trial B u/s

Trial B d/s

Trial D u/s

Trial D d/s

0

10

20

30

40

50

60

70

0 5 10 15 20 25

AFD

M (

g/m

2 )

Days accrual

Trial A u/s

Trial A d/s

Trial B u/s

Trial B d/s

Trial D u/s

Trial D d/s



Figure 3.4: The natural log of periphyton accrual (AFDW) on artificial concrete substrates in the

Manawatu River upstream and downstream of the WWTP discharge (days 0 - 21). Note the relatively

consistent slope (i.e. k value) between each trial during growth phase.

Table 3.2: Periphyton biomass accrual (k, day-1), specific growth rate (µ, divisions/day), P saturated

specific growth rate (µmax, divisions /day), and relative specific growth rates (µ:µmax) for successive trials

in the Manawatu River upstream and downstream of the WWTP discharge. AFDW values were first

converted to equivalent chlorophyll a values before calculating k. A low relative growth rate μ: μmax of

<0.3 indicates growth is limited by low nutrient concentrations, while μ: μmax of >0.8 indicates that

growth is not limited by nutrients.

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 5 10 15 20 25

Ln A

FDM

(g/

m2 )

Days accrual

Trial A d/s

Trial B d/s

Trial D u/s

Trial D d/s

Temp

Trial /site Dates Days (oC) k µ µmax µ:µmax k µ µmax µ:µmax

Trial A d/s 17-24 Jan 7 to 14 20.8 0.24 0.35 0.77 0.46 0.26 0.37 0.77 0.48

Trial B d/s 24-31 Jan 7 to 11 20.8 0.13 0.19 0.77 0.24 0.21 0.30 0.77 0.39

Trial D d/s 23-26 Feb 15 to 18 21.1 0.65 0.94 0.78 1.21 0.24 0.35 0.78 0.45

Trial D u/s 23-26 Feb 15 to 18 21.1 0.67 0.97 0.78 1.25 0.27 0.39 0.78 0.50

Trial D u/s 19-26 Feb 11 to 18 21.1 0.39 0.56 0.78 0.72 0.28 0.41 0.78 0.52

Chlorophyll a AFDM (converted to Chl a )



3.3.2 Periphyton biomass between sites along the river

In order to allow a robust comparison of periphyton biomass between sites, replicate samples were

collected on day 21 in Trials A and D and additional downstream sites sampled for Trial D. Chlorophyll a

and AFDM showed a similar pattern of periphyton biomass changes longitudinally down the river. The

sites 800m and 1200m downstream of the discharge had significantly more periphyton biomass than

upstream, but biomass had declined to less than guideline values by 3.8km downstream (upstream of

Longburn discharges), followed by an increase in biomass downstream of the Longburn discharges (4.7

km downstream of the Totara Road WWTP (see Figure 3.5 and Figure 3.6).

There was no difference in periphyton AFDM between Longburn (3.8 km downstream) and the site

upstream of the WWTP discharge. At the upstream site chlorophyll a was considerably lower than

AFDM compared to the periphyton guidelines. This was observed on all sample occasions with the

exception of the chlorophyll a peak on day 18 during Trial D (see Figures 3.2, 3.3 and 3.5). In contrast,

at the downstream sites chlorophyll a tended to exceed equivalent guideline values considerably earlier

than AFDM; this was particularly apparent during Trials A and B (see Figure 3.2 and 3.3).

Periphyton cover was not measured in the river at Longburn, but it is apparent from photographs in

Appendix 6 that there was considerably more periphyton cover at the Longburn sites compared to

upstream of the discharge – suggesting that AFDM may be over-estimating periphyton biomass at the

upstream site (possibly because it is sampling chironomid cases attached to the tiles).

A similar pattern of periphyton biomass change between sites along the river was found during

periphyton sampling of river substrate two weeks later on 16 March 2013 (Figure 3.7). This sampling

was done in conjunction with macroinvertebrate sampling and collected from riffle habitat rather than

runs.

The sampling sites upstream and downstream of Longburn STP had lower water velocity than the other

sites (i.e. 58 cm/s, 64 cm/s, 44 cm/s, 29 cm/s for sites upstream of the WWTP discharge, 800m

downstream, 1200m downstream and upstream of the Longburn discharges), and this may explain

some, but not all, difference in biomass between sites.

3.3.3 Assessing biomass using AFDM compared to chlorophyll a

The ratio of AFDM to chlorophyll a, i.e. the autotrophic index (AI), was extremely high at the upstream

site with a median value of 650 (see Figure 3.8). At the downstream site there was a difference

between trials, with periphyton during Trials A and B having a median value of 93 compared to

periphyton during Trial D which had a median value of 158 (mean =171). The first sample from Trial D

(day 7) is grouped with Trials A and B (to capture early colonising algae) and an equivalence test

showed that the difference between the earlier samples and the later samples was statistically

significant11. Another way to view this data is to compare the correlation of AFDM and chlorophyll a as

shown in Figure 3.9. This shows a strong relationship between AFDM and chlorophyll a at the

downstream sites during Trial A and B + day 7 of Trial D (r2=0.94), but considerably more variability in AI

during Trial D (days 11-25) (r2=0.79).

11

Student t-test p-value =0.04.



There was no evidence of organic pollution at the upstream site to cause the high AI values. Instead the

high AI was likely to have been due to extensive grazing of periphyton by macroinvertebrates that both

reduce periphyton accrual and turn this into insect biomass that contributes to AFDM. Jernakoff and

Nielsen (1997) found that Gastropods reduced the ratio of chlorophyll a to ash-free dry weight of

periphyton in seagrass meadows by 99%. On two sample occasions during late February and March a

high percentage (73%) of ‘sludge’ was recorded at the upstream site during Horizon RC weekly

assessments while chlorophyll a concentrations were relatively low (i.e. 16-70 mg/m2), and it is likely

that some of the ‘sludge’ was the residual of grazed periphyton, chironomids tubes and free-living

caddis nets, both of which were abundant in the macroinvertebrate samples collected upstream of

Fitzherbert Rd bridge on 1/3/13 in the NRWQN samples (1400 and 1800/m2, respectively (Jon Quinn

pers. comm. 2013)

The difference in the AFDM:chlorophyll a ratio between Trials A+B (10 January to 4 February) and Trial

D (8 February to 5 March) probably reflects a change in the species composition of periphyton in the

river and on the tiles. As discussed previously the species composition on the tiles changed over time

with the filamentous green algae Stigeoclonium sp. being an early colonist, followed by Cladophora sp.

stalked diatoms and cyanobacteria. The same sequence occurred in the river itself with Cladophora sp.

and cyanobacteria being more common later in the summer and hence colonising substrates faster

during Trial D. It appears that the early colonising periphyton (mostly Stigeoclonium sp. ) are rich in

chlorophyll a (a median AI of 93 compared to a typical AI of 175 implied in the NZ periphyton guidelines

(i.e. 35,000 mg AFDM/m2 / 200 mg chl a/m2). The cyanobacteria Phormidium sp. was common at the

downstream site late in the summer and is known to have very high concentrations of chlorophyll a

(Kilroy et al. 2012). Sampling patches of Phormidium sp. on the tiles may explain the occasional low

ratio of AFDW:chlorophyll a during Trial D.

There are several reasons why downstream periphyton had a high concentration of chlorophyll a; firstly

Stigeoclonium sp. was the dominant species in early succession and it has a ‘lean’ structure with little

cellulose. Secondly, the chlorophyll a density within cells may have been responding to high nitrogen

concentrations in the downstream water. Nitrogen is a component of chlorophyll, and nitrogen can

stimulate chlorophyll production without necessarily influencing growth (Menendez et al. 2002),

conversely one of the first symptoms of nitrogen deficiency is a reduction in chlorophyll production

(Meeks 1974 in White and Payne 1977).

One implication of downstream periphyton being rich in chlorophyll a is that measuring periphyton

biomass using chlorophyll a will result in guideline values being exceeded while the AFDM periphyton

biomass is within guideline values (as seen in trials A and B, Figures 3.2 and 3.3). Conversely, at the

upstream site periphyton biomass may be over-estimated if measured using AFDM biomass because of

the influence of chironomid grazers. So which measure of periphyton biomass is more appropriate for

assessing the effects of the Totara Road WWTP discharge on the Manawatu River – chlorophyll a,

AFDM or percent cover (e.g. Peri Weighted Composite Cover)?

Hamill (2012) found that the abundance of mayfly declined downstream of the discharge after

chlorophyll a at the downstream sites increased to between 300 to 450 mg/m2. This is considerably

higher than the chlorophyll a values in the NZ periphyton guidelines (i.e. 120 mg/m2 to 200 mg/m2

depending on algae taxa). Using the AI value of 9312 the range corresponds to 28 g/m2 to 42 g/m2 as

12

This was the median AI for samples dominated by Stigeclonium sp.



AFDM. The middle of this range is 35 g AFDM/m2, which, coincidentally, is the same as the NZ

periphyton guidelines when expressed as AFDM. This suggests that AFDM is a more appropriate

measure to use in the Manawatu River downstream of the discharge for comparing periphyton biomass

against guideline values – particularly in the early stages of colonisation13.

This conclusion is specific to assessing the effects of the Totara Road WWTP discharge to the Manawatu

River. It does not imply changes are needed to regional monitoring programmes which have broader

aims and for which chlorophyll a is often a more versatile measure of periphyton biomass (see

discussion in Biggs and Kilroy 2000).

Measures of periphyton cover (e.g. Peri WCC) provide complementary information to biomass

measures and can be used to test the validity of the results. Periphyton thickness, assessed as the

settled volume of mixed samples, could be used as an inexpensive alternative comparable to AFDM

(see Matheson et al. 2012).

Figure 3.5: Mean periphyton biomass (estimated by chlorophyll a) on concrete tiles in the Manawatu

River after 21 days accrual (1st March 2013). Error bars are 2 standard errors (i.e. 95% confidence). The

red line is the NZ periphyton guideline for trout habitat (diatoms and cyanobacteria).

13

Furthermore, the relative specific growth rates were much more consistent between trials when assessed using AFDM, which is closer to what would be expected between trials separated by only a few weeks (Table 3.2).

0

50

100

150

200

250

300

350

400

450

500

Ch

l a(m

g/m

2)



Figure 3.6: Mean periphyton biomass (estimated by AFDM) on concrete tiles in the Manawatu River

after 21 days accrual (1st March 2013). Error bars are 2 standard errors. The red line is the NZ

periphyton guideline for trout habitat.

Figure 3.7: Periphyton biomass (as chlorophyll a) on Manawatu River cobbles collected from riffle

habitat on 16 March 2013. The red line is the NZ periphyton guideline for trout habitat (diatoms and

cyanobacteria).

0

10

20

30

40

50

60

70

AFD

M (

g/m

2)

0

50

100

150

200

250

300

350

1000m u/s 800m u/s 800m d/s 1000m d/s 3.8km d/s (u/sLongburn)

Ch

l a(m

g/m

2)



Figure 3.8: Comparison of Autotrophic Index (AI) between sites and trials. The difference between Trial

A&B and Trial D was statistically significant.

Figure 3.9: Relationship between AFDM and chlorophyll a comparing sites and trials. D7 refers to the

sample from Trial D on day 7.

AI

(AF

DM

:Chl a)

u/s d/s Trial A&B d/s Trial D0

200

400

600

800

1000

1200

1400

1600

1800

2000

R² = 0.94

R² = 0.79

R² = 0.58

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70 80 90

Ch

loro

ph

yll a

(mg/

m2)

AFDW (g/m2)

d/s Trial A&B + D7

d/s Trial D

u/s



3.4 Summary


While sediments are an important store of phosphorus, this experiment did not support a

hypothesis that phosphorus release to the river was caused by phosphorus concentration

gradients between the water and the sediments (that gradually decline over time). This was

seen in:

o The initial peak in maximum periphyton biomass occurred progressively earlier for

trials later in the summer.

o Periphyton growth rates measured on concrete tiles in Trial A were similar to growth

rates on tiles place in the river a week later (Trial B) despite a longer period of alum

dosing in late summer.

o DRP concentrations in the river downstream of the discharge were very low during

January – within a week of alum dosing recommencing following floods in late

December, while later in the summer DRP concentrations increased.

o Periphyton biomass in the river was higher in the period January to March compared to

November and December despite sediments in late summer having been exposed to a

longer period of relatively low DRP concentrations from alum dosing of the discharge

(see previous chapter).

There is no evidence that undertaking the alum dosing for a longer period of time with the

current treatment system causes any control on downstream periphyton growth.

The maximum periphyton growth rate at the downstream site during Trial D indicated little or

no nutrient limitation, which is consistent with high nutrient concentration in the river during

this period (see Section 2). There was a short period of time during Trial D when the periphyton

growth rate at the upstream site was equivalent to downstream and near maximum.

The stimulatory effect of the discharge on periphyton growth was most evident in the first 1.2

km downstream of the discharge and was considerably less near Longburn 3.8 km downstream.

The periphyton biomass exceeded that 35 g/m2 guideline for protection of trout habitat within

15 to 17 days based on AFDM measurements.

Early colonising periphyton such as Stigeoclonium sp. appeared to be rich in chlorophyll a

compared to AFDM. This caused guideline values to be exceeded earlier when measured using

chlorophyll a compared to AFDM.

Chlorophyll a often over-estimated periphyton biomass at the downstream site (associated

with Stigeoclonium sp.). Conversely AFDM appeared to over-estimate periphyton biomass at

the upstream site because much of the periphyton had been grazed by macroinvertebrates and

AFDM also include biomass of chironomids and caddisfly within the sample).



For sites downstream of the discharge, AFDM is a better measure for assessing periphyton

cover against guideline values because the AFDM guideline value of 35 mg /m2 corresponds to

a decline in mayfly abundance in the river (as reported in Hamill 2012). Percent cover (e.g.

weighted composite cover) provides complementary information that helps confirm biomass

measures.

Additional investigations that would help confirm some of these results includes:

o Undertake specific sampling to assess the ratio of chlorophyll a to AFDM of specific

periphyton species common in the Manawatu River e.g. Stigeoclonium sp, Cladophora

sp, Phormidium sp.



4 Nutrient limitation

4.1 Introduction

Nutrient concentrations have a significant effect on the rate of periphyton growth. Both phosphorus

and nitrogen are thought to have a controlling influence on periphyton growth in the Manawatu River

with the potential controlling nutrient varying in space and time and being highly influenced by river

flow (McArthur et al. 2010). The WWTP relies on alum dosing to remove dissolved phosphorus in order

to limit the rate of periphyton growth in the river.

The results of a periphyton nutrient bioassay done in April 2012 were ambiguous – indicating some

phosphorus limitation but also control by other factors. The periphyton bioassay was repeated in 2013

with some modifications to the method to include:

A treatment of river water mixed with sewage effluent to test for possible effects of

micronutrients, carbon or total ammoniacal N within the effluent, and

Features to discourage and limit the effects of grazing by macroinvertebrates i.e. a Vaseline

petroleum gel barrier around the edge of the trays and the use of felt covers rather than GFC

filters.

Chapter 2 discussed the potential nutrient limitation based on SIN and DRP concentration in the river

water; the experiment described in this chapter provides more definitive results.

4.2 Method

A periphyton nutrient bioassay was undertaken using the steel tray nutrient diffusing substrate (NDS)

method described in Biggs and Kilroy (2000). Two trays were deployed at each site with one tray at

each site containing a treatment of nitrogen+phosphorus+sewage. Each tray had five replicates of four

different treatments. The treatments applied to each tray at each site were:

Trays A and C (downstream and upstream respectively)

i. agar with no enrichment as a control (C),

ii. agar enriched with nitrogen (N),

iii. agar enriched with phosphorus (P),

iv. agar enriched with nitrogen and phosphorus (N+P).

Trays B and D (downstream and upstream respectively)

i. agar with no enrichment as a control (C),

ii. agar enriched with nitrogen (N),

iii. agar enriched with phosphorus (P),



iv. agar enriched with nitrogen and phosphorus and sewage (N+P+S).

The agar treatments were made at CEL Laboratories using the recipe in Biggs and Kilroy (2000).

Nitrogen treatments were made with 42.5 g/L sodium nitrate (NaNO3) (about 7.0 g N/L); phosphorus

treatments were made with 19 g/L trisodium orthophosphate (Na3PO4.12H2O) (about 1.55 g P/L). For

the sewage treatments the N and P were made up with a 1:1 mixture of WWTP sewage and river water,

both collected on the day of preparation. The concentration of DRP and SIN in the 1:1 mix of sewage

and river water was 0.23 mg/L and 17.4 mg/L respectively. Most of the SIN was in the form of

ammoniacal nitrogen. The contribution of sewage to the overall concentration of N and P in the N+P+S

treatment was negligible i.e. about 0.2% and 0.01% extra nutrients for N and P respectively.

The NDS method in Biggs and Kilroy (2000) was modified by: a) attaching felt batting as a substrate to

grow periphyton above each nutrient treatment instead of hardened ashless filter paper, and b)

smearing a layer of petroleum jelly around the edge of each tray. Both of these modifications help

reduce the influence of macroinvertebrate grazers, the felt because it allowed periphyton to grow to

some extent within the felt matrix and the petroleum jelly by deterring some grazers such as snails.

Trays were upstream and downstream of the discharge in similar locations as the concrete tiles (see

Chapter 3), specifically:

Manawatu River about 800m upstream of the discharge point on true left;

Manawatu River about 880m below the discharge point on the true right.

At each site two trays were located side by side in areas with similar depth and velocity and partially

dug into the river bed so that the top was elevated about 4 cm above the river substrate. The trays

were secured to a single waratah via a rope (about 0.6m long). Water depth and velocity were

measured at each side of the tray when they were installed and removed.

Two NDS experiments were placed in the river. The first experiment was installed on 14 February and

removed on 1 March just prior to a small flood. This experiment used hardened ashless filter paper as

per the method in Biggs and Kilroy (2000) and experienced considerable damage by birds to the extent

that one tray had no useable replicates. The top layer of agar from these trays was removed and

replaced with fresh treatment agar. The second experiment used felt substrate over the agar and was

placed in the river on 6 March and removed on 18 March 2013 (i.e. 12 days for accrual).

Felt substrates were removed, stored in a dark chilli-bin, frozen and sent to NIWA for analysis of

chlorophyll a using ethanol extraction method14. The results were converted to mg/m2 based on each

replicate having 6.5cm diameter (0.00332 m2) of surface exposed for periphyton growth.

There was no difference in water velocity between the downstream trays but tray A was in slightly

shallower water (see Table 4.1). There was a similar range of velocity across each of the downstream

trays but at the upstream site the control treatment on tray D was in a zone of higher velocity than the

control treatment of trays C. The nitrogen (N) treatment on tray C was also in a zone of slightly higher

velocity than the N treatment of other trays. Velocity and depth measured when the trays were

removed showed the same pattern across treatments and trays.

14

Blend, filter, boil 5 min in ethanol @78°C, 24hr extraction, spectrophotometer measurement.



There was evidence of grazing by macroinvertebrates on the upstream trays when they were removed

after the first experiment on 1 March (see Figure 4.1a). The second experiment had evidence of

chironomids tubes on the downstream trays (see Figure 4.1b) but little evidence on the upstream trays.

Table 4.1: Water depth and velocity on the corner of each NDS tray when installed on 6 March 2013.

Figure 4.1a: Nutrient diffusing substrates (NDS) installed in the Manawatu River upstream (tray D,

photo on left) and downstream (tray B, photo on right) of the discharge 14 February to 1 March 2013.

Treatments are in order, from left to right, N, P, N+P and C. Evidence of chironomid tubes on upstream

trays, and bird damage on downstream trays.

Site

Treatment C N+P P N C N+P+S P N

depth (cm) 22 21.5 15.5 15.5

velocity (cm/s) 54 54 54 54

Site

Treatment C N+P+S P N C N+P P N

depth (cm) 18 17 16 15.5

velocity (cm/s) 54 58 58 49

TR

bank

TL b

ank

d/s Ad/s B

u/s C u/s D



Figure 4.1b: Nutrient diffusing substrates (NDS) installed in the Manawatu River upstream (tray D,

photo on left) and downstream of the discharge (Tray B, photo on right), on 6 March to 18 March 2013.

Treatments are in order, from left to right, N, P, N+P and C. Evidence of chironomid tubes on

downstream trays.


4.3.1 Comparison between treatments

The nutrient bioassays indicated that periphyton in the Manawatu River upstream of the WWTP

discharge was primarily limited by nitrogen with secondary phosphorus limitation exhibited when

nitrogen was supplied in the N+P and N+P+S treatments. The greatest periphyton stimulation was

caused by treatments with N+P (i.e. including N+P+S), followed by N (Figure 4.2 and Appendix 3 for all

data). Both N+P and N treatments were statistically different from each other, the P treatment and the

control. There was no statistically significant difference between the P treatment and the control (see

Table 4.2).

Downstream of the discharge (trays A and B) there was an indication of dual limitation by N+P+S. No

periphyton stimulation occurred with individual treatments of P, N or N+P, however the N+P+S

treatment did stimulate periphyton growth and resulted in very similar biomass to that found on the

upstream N+P+S treatment (tray C) (see Figure 4.3 and Table 4.2). The lack of response to enrichment

by N at the downstream site is consistent with periphyton being sated by high SIN concentrations in the

river downstream of the discharge (i.e. SIN 0.75 mg N/L, DRP 0.02 mg P/L). Despite the high

concentration of SIN in the river downstream of the discharge the periphyton did not respond to the P

treatment, perhaps reflecting the moderately high levels of DRP in the river (0.016-0.023 mg/L).

Faster water velocity can stimulate faster periphyton growth by increasing the diffusion of nutrients to

growing cells. This effect occurs up to velocities of about 60 cm/s, after which periphyton biomass

tends to reduce due to scouring (Horner et al. 1990) (although scouring is less common in the early

stages of growth when periphyton biomass is low). Horner et al. (1990) found the positive effect of



velocity to be more evident at low (<0.0075 mg/L) DRP concentrations. There were small differences in

water velocity across the upstream trays, but the control treatment responded in the opposite way

than would be expected due to velocity, i.e. there was a little less biomass on tray D. This suggests that

the small velocity difference across and between the upstream trays were insignificant.

The results from the first bioassay (14 Feb-1 March) were consistent with those of the second, showing

primarily nitrogen limitation and secondary phosphorus limitation. Damage to some trays and scouring

of periphyton reduced replicates and increased variability from this experiment so the results are not

presented in detail.

The results confirm that implied by water quality sampling as discussed in Section 2.3.3 i.e. N limitation

at the upstream site but no nutrient limitation at the downstream site in late summer.

Stimulation by sewage + N+P

If there was a stimulatory effect of sewage separate from the nutrients N and P then it should show at

the upstream site more strongly than at the downstream site15. In fact the opposite occurred.

Upstream of the discharge there was no significant difference between the treatments N+P and N+P+S,

while downstream of the discharge there was strong evidence of statistically significant difference (see

Table 4.3 and Figure 4.4). The control treatment in tray C was slightly higher than the control in tray D

and thus the difference between the treatments N+P and N+P+S was further reduced at the upstream

site when statistical analysis was done on the residuals after subtracting the mean values from the

control of each treatment.

The apparent response to the sewage treatment at the downstream site (but not upstream site) may

reflect a poor response to the N+P treatment at the downstream site rather than some stimulation

from the added sewage. The treatment N+P+S had a very similar periphyton biomass at both the

upstream and downstream sites, but the treatment N+P grew more periphyton biomass at the

upstream site (tray D) (150 mg/m2 u/s compared to 112 mg/m2 d/s, see Figure 4.3).

On the whole we cannot rule out the possibility of the sewage providing additional stimulation to

periphyton growth independent of the N and P. Statistical analysis on the combined datasets from

upstream and downstream indicate ‘moderate evidence’ of meaningful difference between the N+P

and N+P+S treatments (Table 4.3).

There are a number of possible reasons for this effect including supply of micronutrients (e.g. cobalt or

molybdenum) as discussed in (Hamill 2012). Hamill (2012) compared the relative composition of

dissolved nutrients in the river (normalised relative to phosphorus) compared to the relative

composition of algae (from Heckey and Kilham 1988). This found nitrogen to be the next most

potentially limiting nutrient after phosphorus, but no sample data was available for cobalt,

molybdenum or silica. River and effluent samples were tested for a suite of micronutrients in December

2012 and January 2013, and the analysis updated (see Table 4.4). Silica was clearly not limiting diatom

growth. The algal requirements for cobalt and molybdenum are so low that laboratory detection limits

were too high to confirm if there might be potential limitation. Raw data from cobalt suggested it was

getting close to concentrations that might limit periphyton growth more strongly than P. No

15

As discussed in the methods, the sewage treatment added negligible additional N and P to the treatments.



molybdenum was detected in river water samples. Molybdenum was detected in the discharge at a

mean concentration of 0.0013 mg/L but cobalt was not detected in the discharge (<0.0005 mg/L).

While we cannot rule out the possibility of the sewage providing additional stimulation to periphyton

growth separate from N and P, even if the effect is real, it remains small compared to the combined

effect of N and P stimulating periphyton growth, and probably of little practical consequence.

Table 4.2: Results of statistical tests comparing treatments at each site. Shaded cells indicate sites with

a statistically significant difference between treatments.

Table 4.3: Results of statistical tests comparing treatments N+P with N+P+S at the upstream and

downstream site. Shaded cells indicate sites with a statistically significant difference between

treatments.

Site C vs P C vs N C vs N+P(+S) P vs N P vs N+P(+S) N vs N+P(+S)

Downstream (grouped) Equivalent Equivalent see below Equivalent see below see below

Upstream (grouped) Equivalent Strong evidence see below Strong evidence see below see below

ds A TR (bank) N+P+S Equivalent Equivalent Strong evidence Equivalent Strong evidence Strong evidence

ds B TL (centre) Equivalent Equivalent Equivalent Equivalent Equivalent Equivalent

us C TL (bank) N+P+S Equivalent Strong evidence Strong evidence Equivalent 1 Strong evidence Strong evidence

us D TR (centre) Equivalent Strong evidence Strong evidence Strong evidence Strong evidence Strong evidence

t-test p-values

ds A TR (bank) N+P+S 0.6 0.8 0.0007 0.8 0.0004 0.006

ds B TL (centre) 1 0.4 0.6 0.2 0.5 0.2

us C TL (bank) N+P+S 0.4 0.006 0.0006 0.06 0.003 0.04

us D TR (centre) 0.7 0.008 0.0002 0.004 0.0001 0.005

Note: Equivalent = t-test p -value >0.05, inequivalence test was accepted and equivalence test was accepted.

1 = In this case the bayesian posterior probability that difference is within limits = 4%,

and there was moderate evidence of a difference on log transformed data (p=0.05).

N+P vs N+P+S equivalence analysis t-test

p -value

Bayesian posterior


is within limits

mean N+P

(mg/m2)

mean N+P+S

(mg/m2)

Upstream Equivalent 0.4 37% 150 170

Downstream strong evidence 0.02 3.3% 112 168

Combined u/s and d/s moderate evidence 0.02 9.2% 131 169


Moderate evoidence = t-test p-value <0.05, inequivalence test was accepted and equivalence test was accepted.



Figure 4.2: Periphyton biomass (measured as chlorophyll a) on NDS at upstream site after 12 days of

accrual (6 March to 18 March 2013). Error bars are 95 percentiles. The dashed red line is the One Plan

periphyton target, included to assist comparison between sites.

Figure 4.3: Periphyton biomass (measured as chlorophyll a) on NDS at downstream site after 12 days of

accrual (6 March to 18 March 2013). Error bars are 95 percentiles. The dashed red line is the One Plan

periphyton target, included to assist comparison between sites.

0

50

100

150

200

C P N N+P+S C P N N+P

Ch

l a(m

g/m

2)

Tray C Tray D

0

50

100

150

200

C P N N+P+S C P N N+P

Ch

l a(m

g/m

2)

Tray A Tray B



Figure 4.4: Comparison of treatment N+P and N+P+S between trays and sites (6-18 March). The

difference between trays A & B (downstream) was statistically significant, but the difference between

trays C & D (upstream) was not. The shaded boxes contain 50% of the data; lines in the boxes are

median values and whiskers show minimum and maximum values.

Chl a (

mg/m

2)

Site A: N+P+S Site B: N+P Site C: N+P+S Site D: N+P0

50

100

150

200

250



Table 4.4: Relative elemental composition of algae (normalised to total dissolved P on a molar basis)

compared to the relative mean concentration of dissolved constituents in the river on 20 Dec, 3 Jan, 9

Jan and 16 Jan 2013. Bold values are similar to algal requirements (adapted from Hecky and Kilham

1988).

4.3.2 Comparison between sites

Periphyton grew significantly faster on control and phosphorus treatments at the downstream site

compared to control treatments at the upstream site (see Figure 4.5 and Table 4.5). There was no

difference in periphyton chlorophyll a between sites for N, N+P or N+P+S treatments (see Table 4.5 and

Figure 4.4). At the downstream site the chlorophyll a was elevated on the C and P treatments to be

similar to that of the N treatment – reflecting the supply of nitrogen from the discharge.

The phosphorus and nitrogen regression models described in Biggs (2000) was used to predict

periphyton biomass that would be expected due to river nutrient concentrations (SIN and DRP) over

the 12-day accrual period of the two NDS bioassays. The regression model predicts maximum

chlorophyll a concentrations as a function of mean days of accrual and mean monthly DRP using data

from 30 New Zealand rivers. This model will, at best, be approximate when applied to a specific river,

but is used here as a tool to examine the effects of nutrients.

Mean chlorophyll a measured on the control treatments was compared with predictions using SIN at

the upstream site and DRP at the downstream site (see bold values in Table 4.6). At the upstream sites

the NDS controls had less chlorophyll a than predicted due to SIN on for the first experiment and more

Element

River u/s

(mg/L)

molar

mass

River u/s

(mols/L) River u/s Algal

N 0.12 14.01 0.0086 26.53 11.1

Si 4.45 28.09 0.1584 490.62 96

K 1.2 39.1 0.0307 95.05 1.3

P 0.01 30.97 0.00032 1.00 1

Na 8.18 22.99 0.3558 1101.93 0.74

Mg 2.4 24.31 0.0987 305.75 0.66

Ca 15.4 40.08 0.3842 1189.97 0.63

S 2.77 32.07 0.0864 267.50 0.54

Fe 0.156 55.85 0.0028 8.65 0.32

Zn 0.00075 65.39 0.000011 0.04 0.012

B 0.022 10.81 0.0020 6.30 0.008

Cu 0.0006 63.55 0.000009 0.03 0.004

Mn 0.0103 54.94 0.00019 0.58 0.003

Co 0.00015 58.93 0.00000 0.008 0.003

Mo <0.0001 95.94 0.000001 <0.003 0.00002

Typical algal composition from Heckey and Kilham (1988)

River concentrations are for dissolved, N = DIN, P = total dissolved P

Cobalt value is median of raw data and error may be >50%.

Composition relative to P



than predicted for the second experiment. At the downstream site the NDS controls had considerably

more periphyton than expected due to DRP for both experiments.

There are a number of possible explanations for the difference between modelled and actual

periphyton growth at the upstream site. Periphyton biomass is likely to have been reduced by

macroinvertebrate grazing during the first experiment and chironmids tubes were seen on the

substrates (see Figure 4.1). In the second experiment, the felt substrates with the petroleum jelly

barrier would have restricted the effects of grazing, the felt also appeared to hold algae fragments

drifting in the water. Therefore some of the chlorophyll a could reflect recruitment from algae drift

rather than algae growth. The higher than expected growth at the downstream site could also reflect

recruitment of algae drifting in the water; alternatively the DRP concentrations in water samples may

be under-estimating the true nutrients available, i.e. periphyton could be obtaining DRP from sediment

trapped in the periphyton mat so the control and N treatments were not really P limited (as discussed

earlier in this report). This possibility is explored in more detail in Section 5.

When periphyton growth rates are low, grazing by macroinvertebrates can be a very significant factor

restricting the accumulation of periphyton biomass. This appeared to be the case during the first

experiment in which very little chlorophyll a accumulated at the upstream site compared to in the

second experiment using felt substrates (i.e. an average biomass at the downstream site of 3.3 mg/m2

compared to 58 mg/m2 for the control of the first and second experiment respectively, corresponding

to an average chlorophyll a accumulation of 0.22 mg/m2/day and 4.86 mg/m2/day respectively).

Figure 4.5: Comparison between downstream (trays A & B) and upstream (tray C & D) sites for control

treatment (left) and phosphorus treatment (right). The shaded boxes contain 50% of the data; lines in

the boxes are median values and whiskers show minimum and maximum values.

Chl a (

mg/m

2)

downs

tream

upst

ream

0

50

100

150

Chl a (

mg/m

2)

downs

tream

upst

ream

0

25

50

75

100

125

150

C P



Table 4.5: Results of statistical tests comparing upstream and downstream at each treatment. Shaded

cells indicate treatments with a statistically significant difference between upstream and downstream.

Table 4.6: Predicted and actual chlorophyll a on NDS control treatment for each period. Chlorophyll a

concentrations modelled using the equation in Biggs (2000) and the measured concentrations of SIN

and DRP. Water quality would predict SIN as most limiting at the upstream site and DRP at the

downstream site.

Pheophytin – degradation

Pheophytin is a degradation product of chlorophyll a and the ratio of Phe to Chl a can indicate the

physical condition for algae. Pheophytin concentration and the percentage of pheophytin to

chlorophyll a showed the opposite pattern across treatments to that of chlorophyll a. This reflected a

negative correlation between pheophytin and chlorophyll a (see Figure 4.6). There was a negative

correlation between log Phe vs. log Chl a at the upstream site (r2=0.54) but not at the downstream site

(r2=0.03). 16

Samples from concrete tiles had a positive correlation between pheophytin and chlorophyll a, so it is

surprising that the correlation on NDS substrates was negative. It may indicate the influence of

macroinvertebrate grazing at the upstream site removing fresh algae biomass and excreting detritus;

the influence of macroinvertebrate grazing would be relatively stronger at low periphyton biomass.

The laboratory found that all samples from trays C and D (18 March) had something interfering with

analysis of acidified samples. This may result from the presence of chlorophyll b or chlorophyll c from

16

Note that the equivalent data from the tiles showed a weak positive correlation between Phe vs Chl a.

u/s vs d/s grouped equivalence analysis t-test

p -value

Bayesian posterior


is within limits

mean

upstream

(mg/m2)

mean

downstream

(mg/m2)

Control Strong evidence 0.001 0.5% 58 97

Phosphorus Strong evidence 0.0007 0.4% 66 102

Nitrogen Equivalent 0.4 38% 103 92

N+P Equivalent 0.12 10% 150 112

N+P+S Equivalent 0.9 56% 170 168


Experiment site

accrual

period

DRP

(mg/m3)

SIN

(mg/m3)

DRP

Predicted

max Chl a

(mg/m2)

SIN

Predicted

max Chl a

(mg/m2)

Measured

Chl a

(mg/m2)

NDS 14 Feb -1 March 13 u/s 15 12.3 3.74 72 13 3.3

NDS 14 Feb -1 March 13 d/s 15 22 755 96 182 159.4

NDS 6 March -18 March 13 u/s 12 14 6.8 46 10 58.3

NDS 6 March -18 March 13 d/s 12 19.6 757 54 112 96.9

Note: SIN and DRP = mean of data for period. Period 14 Feb to 1 March n=10; period 6 March to 18 March n=5.



particular algae species interfering with the acidification method for calculating chlorophyll a and

pheophytin (see Stich and Brinker 2005), although it is doubtful that the substrates would have

significantly different species composition between upstream and downstream.

Figure 4.6: Negative correlation between chlorophyll a and pheophytin. R2=0.51 on log transformed

data.

4.4 Summary


The nutrient bioassays indicated that periphyton in the Manawatu River upstream of the

WWTP discharge from mid-February to mid-march was primarily limited by nitrogen with

secondary phosphorus limitation exhibited when nitrogen was supplied in the N+P and N+P+S

treatments. This is consistent with the results of water quality analysis in Chapter 2.3.3.

Periphyton growth in the river downstream of the WWTP showed a small amount of dual

limitation by N+P.

There was evidence that some characteristic of the sewage stimulated periphyton growth in

addition to the N and P; however the effect was small compared to the combined effect of N

and P stimulating periphyton growth and of little practical consequence.

y = 0.20x + 0.55R² = 0.03

y = -0.66x + 2.40R² = 0.51

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.40 1.60 1.80 2.00 2.20 2.40

Log1

0 p

heo

ph

ytin

Log10 chlorphyll a (mg/m2)

downstream

upstream



Despite high concentrations of SIN in the river downstream of the discharge, the P treatment

did not stimulate periphyton growth – indicating that periphyton was obtaining sufficient DRP

from the water and/or by extracting P from sediments trapped in their mat (see next section).

Periphyton grew significantly faster on control treatments at the downstream site compared to

control treatments at the upstream site. The amount of periphyton biomass at the downstream

site was more than expected due to DRP in the river water – suggesting either recruitment of

drifting periphyton fragments or water samples under-estimating the true nutrients available,

e.g. from sediment trapped in the periphyton mat.

Grazing by macroinvertebrate plays an important role in controlling periphyton biomass. This

was highlighted by periphyton accumulation at the upstream site on felt substrates that limited

the impact of macroinvertebrate grazing.

The nitrogen limitation found during experiments in February-March 2013 contrasted with

results from April 2012 which found evidence of phosphorus limitation. These different results

largely reflect the different river conditions and background concentrations of N and P in the

river.



5 Supply of dissolved phosphorus from river sediments

5.1 Introduction

Previous investigations in the Manawatu River have found more DRP in the river than could be

explained by loads from the WWTP discharge, furthermore the periphyton growth downstream of the

discharge was more rapid than could be explained by measured concentrations of DRP in the water.

Hamill (2012) speculated that this could be due to the storage and release of P from river sediments. A

number of studies have shown that river sediments can store and release phosphorus (e.g. Stutter et al.

2010) due to changing phosphorus concentrations from sewage discharges. This biogeochemical

process can be driven by concentration gradients as well as biological activity and changes in oxygen

and pH at the sediment interface (e.g. Afsar et al. 2012)

Extensive and actively growing periphyton can cause substantial diurnal fluctuations in river water pH

and dissolved oxygen – increasing during the day and decreasing at night. The magnitude of these

fluctuations is greater near and within the periphyton mats, where pH can range up to pH 9.5 or 10.

Even under oxygenated conditions high pH can cause phosphorus bound to iron or aluminium within

sediments to dissolve and become available for periphyton uptake or release to the water column.

Initial measurements in the Manawatu River (January 2013) found dissolved oxygen in river pore water

to be reasonably well oxygenated (e.g. about 5 mg/L), so the focus of our investigations have been on

the effect of pH fluctuations on release of dissolved phosphorus. This chapter presents the results of

three simple investigations:

Spatial change in stream pH and nutrients between the periphyton interface and flowing river

water;

Sampling water quality of pore water amongst the river gravels;

The effect of pH on the release of dissolved phosphorus from sediment deposited on and

trapped within the periphyton mat.

5.2 Methods

5.2.1 Phosphorus and pH at periphyton interface

To assess the extent to which periphyton can change pH in their immediate environment, field

measurements of pH and dissolved oxygen (DO) were taken in the Manawatu River 800 to 1000m

downstream of the WWTP discharge during mid-afternoon on 10 January and 29 January 2013. The

measurements were made in a range of habitats including runs, riffles and directly adjacent to the

periphyton mats.

DRP and pH in water samples collected from immediately above/within periphyton mats were

compared with that in samples collected at the same time from the river. It was hypothesised that a

higher DRP concentration at the periphyton interface would indicate release of nutrients from the



sediment to the water column while a lower concentration would indicate periphyton were ‘hungry’ for

nutrients from the water column and possibly also the sediment.

Water samples were collected at the site about 800m downstream of the discharge on 29 January 2013

during a period of low flows and high periphyton cover. A large gauge syringe was used to collect six (6)

replicate samples from immediately above and amongst periphyton mats, and two (2) replicate

samples from the over lying river water at about 30 to 40cm depth. Sampling occurred about 3:15pm

on a fine day to coincide with a high photosynthetic activity. The periphyton sampled was dominated

by either Phormidium sp. or Stigeoclonium sp.

Water samples were stored in a chilli-bin and transported to CEL Laboratories for analysis of dissolved

reactive phosphorus and pH. Field measurements were made of pH and dissolved oxygen.

5.2.2 Water quality of river sediment pore-water

The Manawatu River has zones of down-welling where some of the river water flows through the river

gravels and zones of upwelling where it returns back to river. As the water flows through river gravels

there is potential for both nutrient removal (e.g. through denitrification) or increase of nutrients as

some dissolved nutrients in pore-water are carried back to the river.

The pore-water amongst river gravels was sampled at the sites 1000m upstream of the discharge (TR)

and 800m downstream of the discharge (TR) and the water quality compared with samples collected at

the same time from the overlying river water17. Samples were collected in the early afternoon on 7

March 2013.

Pore-water samples were collected from a depth of 25-28cm below the river bed using a stainless steel

piezometer rammed into the river bed. The piezometer was purged using a hand pump by removing at

least four times the volume of the tube prior to collecting the sample. Overlying water above the

sample points was between 15 and 25 cm deep.

Five replicate samples were collected from the downstream site but only one sample was collected

from the upstream site due to equipment failure. Duplicate river water samples were collected from

both sites before and after completing the pore water sampling.

Prior to sampling it was confirmed that there were zones of down-welling in sections of the Manawatu

River above riffles at both the upstream and downstream site. This was done using a simple test of

digging a hole about 0.5m from the water’s edge, allowing time (about 5-10 minutes) for water level in

the holes to stabilise and measuring the difference in water level compared to that of the river18.

Above riffles, the water in holes at the river edge was about 5-15cm lower than the river water –

suggesting a zone of down-welling water; below riffles and along runs there was little difference in

water level.

17

Note that the upstream site was 200m upstream of where concrete tiles had been place. 18

The method assumes a strong connection between the between shallow groundwater and surface water through the gravel/cobble riverbed. This seemed reasonable because of their water drained quickly out of the holes.



5.2.3 Release of phosphorus from sediment trapped within the periphyton mat

Sediment trapped within the periphyton mat itself was sampled to assess the extent to which this

trapped sediment released dissolved phosphorus in response to pH changes. This provided an estimate

of phosphorus release from sediment in direct contact with periphyton cells.

Prior to undertaking this experiment (on 6 March 2013) a pilot experiment had been carried out on 10

January 2013) by collecting a suspension of deposited sediments from the stream bed (using the

Quorer sampling technique (Harding et al. 2009)) and assessing the effects of pH changes on dissolved

nutrients. The sampling method avoided sediment trapped within the periphyton mat. Therefore the

extent of pH fluctuations experienced by collected sediment was uncertain. The results are not

presented in this report, but were similar to the results of sediment trapped within the periphyton mat,

i.e. a pH increase released more dissolved P and dissolved aluminium and the effect was strongest at

the downstream site.

Sediment samples were collected on 6 March 2013 from the sites 1000m upstream of the discharge (TR

bank at 11am) and 800m downstream of the discharge (TR bank at 8:30am). Five (5) replicate samples

were collected from each site by selecting cobbles covered in periphyton and using distilled water to

flush the fine sediments out of the periphyton mats, through a 500µm net (to exclude coarse material

or invertebrates) and into a sample container. Sediment from one to three cobbles were bulked for

each replicate forming a total sample area for each replicate of between 160cm2 to 295 cm2 (see Figure

5.1 for example of cobbles sampled). Gloves were worn to minimise potential contamination.

All cobbles were collected from flowing water 5cm to 30cm deep. The dominant periphyton species on

the cobbles sampled at both upstream and downstream sites was the filamentous green algae

Cladophora sp. (generally about 1-2cm length).

The dimensions and shape of each cobble were recorded to allow the sample area to be estimated

using an online polygon area calculator (http://www.mathsisfun.com/geometry/area-polygon-

drawing.html). This allowed the results to be expressed in terms of square metres.

Samples were stored in a cool, dark chilli-bin and transported to CEL Laboratories. At the laboratory,

samples of sediment suspension were mixed and analysed for: total suspended solids (TSS), volatile

suspended solids, total aluminium (Al), dissolved Al, total iron (Fe), dissolved Fe, total calcium (Ca),

dissolved Ca, total phosphorus (TP), dissolved reactive phosphorus (DRP), nitrate-nitrite nitrogen

(NNN), total ammoniacal nitrogen, total nitrogen (TN), pH, dissolved oxygen and electrical conductivity.

Sub-samples were taken of the suspensions of trapped sediment and treated as follows: a) adjust to pH

8.5, b) adjust to pH 9.5. The pH was adjusted using a sodium hydroxide solution19, were mixed and left

for half an hour, than sampled, filtered (0.45 micron filter) and analysed for: pH, dissolved Al, dissolved

Fe, dissolved Ca, and DRP.

19

Adjusting pH using bicarbonate would have probably better represented processes influencing pH in the river but sodium hydroxide allowed a much more stable pH adjustment.



Figure 5.1: Selected cobbles from which sediment deposited within the periphyton mat were sampled

(upstream site on left, downstream site on right). The dominant periphyton species on these cobbles

was Cladophora sp.


5.3.1 Phosphorus and pH at periphyton interface

On 10 January 2013 pH and DO in the river water close to the surface of periphyton mats were 8.4 and

131% respectively in the mid-afternoon compared to 7.4 and 87% respectively in the early morning

(7am). These measurements indicated the extent of pH and DO shifts caused by photosynthetic activity.

Measurements on 29 January indicated a high level of photosynthetic activity with high pH (up to 9.6)

and high DO (up to 125%) especially in shallow water and close to the surface of periphyton mats

(Table 5.1).

Water samples collected 29 January) showed lower DRP concentrations within and immediately above

the periphyton mat than in the overlying river water (see Figure 5.2, median of 0.004 mg/L in the mat

and 0.017 mg/L in the river water20). The samples from the periphyton interface also had slightly lower

pH (pH 8.1 compared to 8.4), which is surprising considering samples were collected about 3pm in the

afternoon and close to peak photosynthetic activity. The difference was less than the standard

deviation and may have been caused by sediment within the algae mat being entrained with the

sample.

The results indicate that, during this period, the periphyton at the downstream site was taking

dissolved phosphorus from the river water rather than releasing P to the water column, i.e. the

periphyton was hungry for P. This is consistent with observations during January 2013 of periphyton

increasing in biomass (actively growing) and generally low DRP concentration in the surrounding river

water (see Chapter 2).

20

River samples at the downstream site on the following day had lower DRP, i.e. 0.006 mg/L.



Table 5.1: In-situ field measurements of pH, dissolved oxygen and temperature in the Manawatu River

and amongst periphyton on 29 January 2013, 3:30pm.

Figure 5.2: Comparison of DRP at the periphyton interface and overlying river water (29 January 2013).

Error bars are two standard errors for the periphyton interface and the range for river water samples.

5.3.2 Water quality of river sediment pore-water

The pore-water of river sediments at the upstream site had more SIN and DRP than in the river as

would be expected (Table 5.2). At the downstream site pore water had similar DRP but less SIN

compared to river water - suggesting some attenuation or denitrification may be occurring in the river

sediments. The water quality of pore-water reflected that of the river water with higher concentrations

of dissolved nutrients at the downstream site compared to upstream (Table 5.2). The pore-water pH

was neutral (7.6 and 7.3 at the upstream and downstream site respectively) and reasonably well

oxygenated (DO = 5.9 mg/L).

The results suggest that down-welling river water flowing through the gravel substrate at the upstream

site could pick up some additional SIN and DRP to support periphyton growth when the water returns

to the river. However there was no evidence of pore water contributing to dissolved nutrients in the

river at the downstream site. Instead the there is some evidence of possible denitrification occurring in

Manawatu River d/s WWTP

Depth

(cm) pH DO %

DO

(mg/L)

temperature

(oC)

main river flow 800m d/s 35 8.5 122.0 10.21 22.8

main current d/s riffle 1000m d/s 30 8.85 136.2 11.7 23.2

over riffle 950m d/s 20 9.11 140.0 11.82 24.2

among periphyton 10 9.5 142.0 12.2 25.3

backwater at periphyton interface 10 9.61 124.5 10.12 26.7

Periphyton interface 20 9.36 160.5 13.7 23.5

0

0.005

0.01

0.015

0.02

0.025

0.03

Periphyoninterface

River water

DR

P (

g/m

3)



the river sediments at the downstream site. These results are only indicative because of the lack of

replicate samples at the upstream site.

Table 5.2: Median water quality in pore water of river gravels (6 March 2013).

5.3.3 Release of phosphorus from sediment trapped within the periphyton mat

Characteristics of trapped sediment at each site

The water quality results from replicate samples of trapped sediment before and after adjusting pH

upward are shown in Appendix 4.

The downstream site was characterised by slightly less sediment than upstream and a sediment quality

less rich in iron. Organic matter (VSS) comprised about 9% of the sampled sediment at both sites which

gives confidence that responses to pH changes were being caused by inorganic sediment fractions (see

Table 5.3 and 5.4). There was evidence of effects of the WWTP discharge on sediment quality through

higher concentrations of total ammoniacal N and slightly lower pH. Median total phosphorus was

higher downstream but the difference was not statistically significant (Table 5.3 and 5.4).

Although there was similar or more total phosphorus in the trapped sediment at the downstream site,

there was considerably less DRP and a lower ratio of DRP:TP (see Figure 5.3 and Figure 5.4). Even after

the pH was increased to 8.5 and 9.5 there was less DRP at the downstream site compared to the

unadjusted samples upstream (Figure 5.4). Periphyton growth at the upstream site was limited by low

concentrations of SIN (see discussion on nutrient limitation in chapter 4), which would account for why

the DRP within the periphyton mat at the upstream site not being utilised. In contrast the downstream

periphyton had no N limitation, allowing faster periphyton growth and more demand for DRP which

would be extracted from the surrounding water.

The upstream site had more total aluminium (Al) and there was no significant difference in the

concentration of dissolved aluminium between sites, suggesting that Al associated with natural river

sediments (e.g. clay) had more effect on sediment quality than any residual alum from the discharge

(Table 5.4).

Site

DO

(g/m3) pH

NH4-N

(g/m3)

NNN

(g/m3)

SIN

(g/m3)

Total N

(g/m3)

DRP

(g/m3)

TP

(g/m3)

Al diss

(g/m3)

Al Total

(g/m3)

Fe diss

(g/m3)

Fe Total

(g/m3)

Pore water downstream 5.9 7.3 0.457 0.185 0.763 0.0307 1.253

Pore water upstream 7.6 0.000 0.042 0.042 0.0180 0.928

River downstream 7.8 0.801 0.069 0.870 1.176 0.0288 0.037 0.075 0.115 0.034 5.50

River upstream 7.7 0.000 0.008 0.008 0.089 0.0079 0.017 0.012 0.029 0.042 6.26

Pore water downstream

2x standard error0.213 0.290 0.212 0.255 0.0043 0.633

n=5 for downstream porewater, n=2 for river water, n=1 for upstream porewater.



Table 5.3: Median water quality data from suspension of trapped sediment before and after pH

adjustment. Note that all concentrations are per unit area (m2) of river bed.

Table 5.4: Strength of evidence of a statistical difference in trapped sediment chemistry between sites

upstream and downstream of the discharge. Shaded cells show some evidence of a statistically

significant difference.

Site &

treatmentpH

sample

area

(cm2)

Al Total

(mg/m2)

Fe Total

(mg/m2)

Ca Total

(mg/m2)

Al

dissolved

(mg/m2)

Fe

dissolved

(mg/m2)

Ca

dissolved

(mg/m2)

DRP

(mg/m2)

TP

(mg/m2)

NH4-N

(mg/m2)

SIN

(mg/m2)

TSS

(mg/m2)%VSS

d/s original 6.75 227.6 1210.5 1750.6 982.0 2.47 1.46 180.8 0.395 60.72 13.05 16.68 161262 8.6%

d/s pH 8.5 8.52 227.6 4.45 1.54 194.2 0.800

d/s pH 9.5 9.48 227.6 9.78 1.69 131.9 1.358

u/s original 6.97 175.4 2525.5 4287.6 1349.3 1.95 3.33 153.9 2.240 53.42 5.42 5.93 186354 9.2%

u/s pH 8.5 8.51 175.4 2.78 3.88 130.7 2.155

u/s pH 9.5 9.51 175.4 3.11 3.68 113.0 2.828

Site &

treatmentAl:TSS Ca:TSS Fe:TSS TP:TSS DRP:TSS DRP:TP

DRP

released

(mg/m2)

diss Al

released

(mg/m2)

diss Ca

released

(mg/m2)

diss Fe

released

(mg/m2)

% change

DRP

% change

diss Al

% change

diss Ca

% change

diss Fe

d/s original 0.911% 0.0073 1.38% 0.036% 0.0003% 0.651%

d/s pH 8.5 0.376 1.977 -4.71 0.089 102.2% 80.6% -3.8% 8.7%

d/s pH 9.5 0.702 7.304 -40.06 0.098 243.3% 295.2% -22.9% 3.6%

u/s original 1.175% 0.0066 1.99% 0.025% 0.0012% 4.749%

u/s pH 8.5 -0.436 0.258 -16.26 0.221 -23.5% 16.1% -11.1% 8.2%

u/s pH 9.5 0.481 0.950 -33.26 0.078 12.5% 35.2% -25.5% 2.0%

Variable raw data pH 8.5 pH 9.5

pH Moderate evidence ds<us 1 equivalent equivalent

TP equivalent na na

DRP Strong evidence ds<us note 3 equivalent equivalent

SIN Strong evidence ds>us na na

TSS equivalent na na

VSS equivalent na na

Al dissolved equivalent Strong evidence ds>us Strong evidence ds>us

total Al Strong evidence ds<us na na

dissoved Ca equivalent equivalent equivalent

total Ca Strong evidence ds<us na na

dissolved Fe Strong evidence ds<us Strong evidence ds<us Strong evidence ds<us

total Fe Strong evidence ds<us na na

Al:TSS equivalent na na

Ca:TSS equivalent na na

Fe:TSS Strong evidence ds<us na na

TP:TSS equivalent na na

DRP:TP Strong evidence ds<us na na

DRP released na Strong evidence ds>us equivalent note 2

Al released na Strong evidence ds>us Strong evidence ds>us

Fe released na equivalent equivalent

Ca released na equivalent equivalent

1. pH difference was only meaningful at 5%

2. DRP released, bayesian posterior probability that differnence was within limits was <4%

3. A significant difference found on square root transformed data only.



Figure 5.3: Box plot showing ratio of TP:TSS and DRP to TP in the suspensions of trapped sediment

comparing sites and treatments. The shaded boxes contain 50% of the data; lines in the boxes are

median values and whiskers show minimum and maximum values.

Effect of pH on dissolved nutrients from trapped sediment

There was considerable variation in DRP and dissolved metals between replicates at each site (see

Figure 5.4 to 5.7), so the effect of pH treatments is most easily seen by pairing treatments for each

replicate and comparing the differences (see Figure 5.8 to 5.12). Statistical analysis compared paired

samples of the square root transformed data and the binomial probability statistic was calculated

based on whether the pH treatment caused an increase or decrease in concentration (assuming the

probability of no effect was 50:50) (see Table 5.5).

Increasing the pH of trapped sediment from the downstream site to 8.5 caused a significant increase in

DRP and dissolved aluminium (Al). An increase to pH 9.5 caused more to be released (see Figure 5.8 to

5.10 and Table 5.5). The effect of pH on dissolved Fe and Ca in downstream sediment was equivocal,

with more iron released at pH 8.5 but not significantly more at pH 9.5. Dissolved calcium declined as pH

increased to 9.5 (Figure 5.11 – 5.12).

Trapped sediment from the upstream site showed a different response to increases in pH. There was

no significant increase in DRP or Al at pH 8.5, but there was a response at pH 9.5 (Figure 5.8 to 5.10,

Table 5.5). The absolute amount of DRP released from upstream sediment at pH 9.5 was similar to that

released from downstream sediment at pH 8.5, but the percent increase was very small (a 243%

increase at the downstream site compared to only a 13% at the upstream site), perhaps because DRP

within the upstream mats was already high (Figure 5.8 and 5.9).

Dissolved iron did not respond to the pH increases at the upstream site and dissolved calcium declined

as pH increased to 9.5.

The downstream sample with the highest DRP (and TSS) came from a backwater where the surrounding

cover of periphyton was relatively sparse. The percentage of DRP:TP in this replicate was 4% which was

TP

:TS

S

d/s ra

w

u/s ra

w

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

DR

P:T

P

d/s ra

w

u/s ra

w

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07



closer to the upstream percentage (median 4.7%) than the downstream (median 0.7%). This sample

also had the greatest release of DRP due to pH which suggests that the strong response to pH at the

downstream site was due to characteristics of the sediment (e.g. the influence of alum floc) rather than

being related to a lower initial DRP concentration.

Periphyton is known to use P from sediment on the river bed. Both the surface-bound organic-P and

inorganic-P are readily taken up by algae that are in contact with sediment. Stream bed sediments are

also know to release a small fraction (about 2%) of PP into the river water as DRP by mineralisation,

desorption and/or reducing conditions (Hedley 1978 in Parfitt et al. 2007). The pH driven response

caused by our experiment is consistent with this finding (i.e. releasing 1-2% of the particulate P as DRP).

The weak response of sediment at the upstream site to releasing DRP compared to the downstream

site may reflect the ability of natural river sediments to bind phosphorus more tightly. P in sediment

derived from stream bank material is less available to algae than P in sediment from farm runoff

(McDowell and Wilcock 2007, Hedley 1978). Afsar et al. (2012) found that freshly sorbed phosphates

can be readily desorbed from soil colloids, and the same is likely from residual alum floc discharged in

the effluent.

Extent to which trapped sediment meet periphyton growth requirements

This experiment was not designed to estimate the flux of P from trapped sediments. Nevertheless

calculations indicate that the quantity of DRP released during a half hour extraction by solely elevating

pH was in the ball park to account for a large portion of the periphyton growth requirements. Our

experiment found up to 0.7 mg P/m2 was released from trapped sediments during a half hour

extraction. This source of P might be available for about 8 hours a day when photosynthesis is causing

high pH. Recent experiments in the Tukituki River have found that periphyton (incl. Stigeoclonium sp.

and Cladophora sp.) had DRP uptake rates typically less than 0.62 mg/m2/hr (90th percentile of chamber

experiments) and that the DRP uptake rate was similar during both day and night (John Quinn pers.

comm. 2013). Thus the release from trapped sediment appears to be sufficient to meet day time

growth requirements. This assumes that longer exposures to high pH will continue to extract DRP from

the sediment, but this assumption seems reasonable considering that the trapped sediments were not

‘fresh’ and had already been exposed to diurnally high pH in the periphyton mats which may have

depleted the supply of extractable phosphorus prior to collection. Further work is required to better

understand the kinetics of P release (e.g. experiments using a time series of pH adjustments).

Another way to assess whether the magnitude of what is supplied by the sediment is sufficient to

support periphyton growth is to convert the areal concentration (mg/m2) to a volume concentration

(mg/m3), and compare with periphyton nutrient requirements. Assuming a depth of 3cm of overlying

water influencing the periphyton then the values in Table 5.3 can be multiplied by 12 to convert to

mg/m3. At the downstream site this gives a theoretical initial concentration of SIN and DRP of 200

mg/m3 and 4.7 mg/m3 respectively, i.e. indicative of potential DRP limitation21 but minor SIN limitation.

At the upstream site this calculation gives a theoretical initial concentration of SIN and DRP of 71

mg/m3 and 27 mg/m3 respectively, i.e. indicative of potential N limitation but not DRP limitation.

21

Note that at a cellular level much lower concentrations of DRP may be need to for P saturated growth e.g. 2-4 mg/m

3 (Bothwell 1989).



Table 5.5: Strength of evidence of a statistical difference between raw data and pH adjusted

treatments of sediment trapped by periphyton. Shaded cells show some evidence of a statistically

significant difference. The results are for a paired sample equivalence test on square root transformed

data, and from a binomial probability test.

Figure 5.4: Box plot of DRP in the suspensions of trapped sediment comparing sites and treatments.

The shaded boxes contain 50% of the data; lines in the boxes are median values and whiskers show

minimum and maximum values.

Paired sample equivalence test on square root transformed date

raw vs pH8.5 raw vs pH8.5 raw vs pH9.5 raw vs pH9.5

Variable d/s u/s d/s u/s

DRPstrong evidence

raw<pH8.5equivalent

strong evidence

raw<pH9.5equivalent

Dissolved Alstrong evidence

raw<pH8.5equivalent

strong evidence

raw<pH9.5

strong evidence

raw<pH9.6

Dissolved Fe equivalent equivalent equivalent equivalent

Dissolved Ca equivalent equivalentstrong evidence

raw>pH9.5

strong evidence

raw>pH9.6

Binomial probability test

DRP 0.03 0.16 0.03 0.03

Dissolved Al 0.03 0.16 0.03 0.03

Dissolved Fe 0.03 0.3 0.3 0.16

DR

P (

mg/m

2)

d/s ra

w

d/s pH

8.5

d/s pH

9.5

u/s ra

w

u/s pH

8.5

u/s pH

9.5

0

1

2

3

4

5

6

7

8



Figure 5.5: Box plot of dissolved aluminium in the suspensions of trapped sediment comparing sites and

treatments.

Figure 5.6: Box plot of dissolved iron in the suspensions of trapped sediment comparing sites and

treatments.

Figure 5.7: Box plot of dissolved calcium in the suspensions of trapped sediment comparing sites and

treatments.

Al dis

solv

ed (

mg/m

2)

d/s ra

w

d/s pH

8.5

d/s pH

9.5

u/s ra

w

u/s pH

8.5

u/s pH

9.5

0

5

10

15

20

25F

e D

issolv

ed (

mg/m

2)

d/s ra

w

d/s pH

8.5

d/s pH

9.5

u/s ra

w

u/s pH

8.5

u/s pH

9.5

0

1

2

3

4

5

6

Ca-

Dis

solv

ed (

mg/m

2)

d/s ra

w

d/s pH

8.5

d/s pH

9.5

u/s ra

w

u/s pH

8.5

u/s pH

9.5

0

25

50

75

100

125

150

175

200

225

250



Figure 5.8: Average change in DRP in the suspensions of trapped sediment due to increasing the pH.

Upper error bar is two times the standard error, lower error bar is minimum value. Note that these

average values are larger than the median values presented in Table 5.3.

Figure 5.9: Average percent change in DRP in the suspensions of trapped sediment due to increasing

the pH. Upper error bar is two times the standard error, lower error bar is minimum value. Note that

these average values are larger than the median values presented in Table 5.3.

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Rel

ease

d D

RP

(m

g/m

2)

-100

0

100

200

300

400

500

600

700

800

900

% D

RP

rel

ease

d



Figure 5.10: Average change in dissolved aluminium in the suspensions of trapped sediment due to

increasing the pH. Error bars and two times the standard error. Note that these average values are

larger than the median values presented in Table 5.3.

Figure 5.11: Average change in dissolved iron in the suspensions of trapped sediment due to increasing

the pH. Error bars and two times the standard error. Note that these average values are larger than the

median values presented in Table 5.3.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

Rel

ease

d d

isso

lved

Al (

mg/

m2)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Rel

ease

d d

isso

lved

Fe

(mg/

m2)



Figure 5.12: Average change in dissolved calcium in the suspensions of trapped sediment due to

increasing the pH. Error bars and two times the standard error.

Periphyton ability to capture sediment

It is well known that periphyton is effective at trapping fine sediment within their mats. Davies-Colley

et al. (1992) found that periphyton were effective at trapping fine suspended clay despite the clay’s

extremely low settling velocities (<1 µm/s). This decreased the organic content of the periphyton from

19% to 8.5%. It is probably that fine floc from alum that is released with the WWTP discharge may be

trapped in the periphyton mat. Although there was no significant difference in turbidity in the river

upstream and downstream of the WWTP (see Table 2.2), there is indirect evidence that more inorganic

sediment was being trapped by periphyton and settling on the river bed downstream of the WWTP

discharge.

Firstly, more fine sediment was observed to have accumulated inside the nutrient diffusing substrate

trays at the downstream site (about 10mm) compared to the upstream site (about 2mm) (L. Brown

pers. comm. 2013).

Secondly, although there was no noticeable difference in the organic matter content of periphyton on

tiles upstream and downstream of the discharge (a mean of 13 % at both sites, see Appendix 2), when

the data were filtered to compare similar amounts of biomass between sites (i.e. AFDM between 10

and 40 g/m2) there was significantly22 lower % organic content at the downstream site (i.e. a mean of

17.2 and 12.1 g/m2 respectively upstream and downstream). This was a localised effect and the organic

content in periphyton 3.8km downstream near Longburn was similar to that at the upstream site. This

22

Equivalence test = strong evidence of a practically important difference; t-test p-value = 0.002.

-70

-60

-50

-40

-30

-20

-10

0

10

20

Rel

ease

d d

isso

lved

Ca

(mg/

m2)



suggests that periphyton within about 1km of the discharge was trapping more inorganic sediment for

a given biomass compared to upstream.

Thirdly, the trapped within periphyton mats at the downstream site had a lower pH compared to that

upstream which would be consistent with an influence of alum floc from the effluent discharge.

During the initial phases of growth periphyton require only very low nutrient concentrations (e.g. 2-4

mg/m3 for diatom growth in Canterbury Biggs 1990). As the periphyton mat becomes thicker cells

within the mat become limited and higher concentrations of phosphorus in the water is required to

maintain the growth rate of those deeper in the matrix by increasing the supply rate (Bothwell 1989).

Thus the phosphorus guidelines to prevent the excessive growth of periphyton mats are many times

higher than what is needed for thin layers of individual cells. Periphyton will be much less reliant on

river phosphorus concentrations if it can trap sediment within its mat as it grows and then extract

dissolved P from the sediment.

The thicker periphyton mats grow the more sediment they trap. This was evidenced by the inorganic

content of periphyton mat (i.e., the ash mass in Appendix 2) increasing with periphyton biomass

(AFDM) (r2=0.58, n=22 at the downstream site). The percent organic content also increased with

biomass (AFDM) (r2 =0.4 and 0.3 at for upstream and downstream sites respectively). This explains why

there was no noticeable difference in the organic matter content of periphyton on tiles upstream and

downstream of the discharge (a mean of 13 % at both sites) if the data were not first filtered.

5.4 Summary


Periphyton can cause large pH fluctuations in surrounding river water (measured up to pH 9.6

close to the periphyton mat). During January 2013 the periphyton was actively growing and

extracting DRP from the overlying river water – i.e. it was hungry for phosphorus.

The pore water amongst the river gravels does not appear to be a source of dissolved nutrients

at the downstream site.

It is possible that river sediment at the downstream site is attenuating or removing some

nitrogen. This is indicated by lower SIN in the sediment pore water compared to the overlying

river water.

Periphyton can trap fine sediment within their mat. There was evidence that more fine

sediment is trapped in periphyton mats downstream of the WWTP once data was adjusted for

biomass. The lower pH and higher dissolved Al suggests some contribution of alum floc.

There was more DRP in trapped sediment at the upstream site which reflects periphyton

utilising less DRP compared to downstream - probably due to N limiting periphyton growth

upstream of the discharge.



Increasing the pH of trapped sediment from the downstream site caused a significant increase

in DRP, i.e. pH 8.5 = 102% increase, pH 9.5 = 243% increase. The response to pH at the

upstream site was much weaker with no significant increase in DRP at pH 8.5 and a 13%

increase at pH 9.5. The different response to pH was attributed to the WWTP discharge.

Release of dissolved Al from sediments showed a similar pattern to DRP, responding strongly to

pH increases at the downstream site but more weakly at the upstream site – pointing to the

different responses being due to deposition of alum floc.

Periphyton can trap more fine sediment as it grows thicker. The sediment continually trapped

within the mats becomes a potential source of phosphorus that is released when

photosynthesis causes a sufficient increase in pH. Our results indicate that this mechanism for

periphyton to obtain P is particularly strong downstream of the WWTP discharge, possibly

because the P attached to the fine alum floc is weakly bound.

The results of these investigations could be further confirmed by:

o Regular sampling of pH and nutrients at the periphyton interface and overlying river

water throughout a summer period covering a periphyton accrual phase and a loss

phase.

o Confirm evidence of more fine sediment settling downstream of the WWTP by

installing sediment traps in the river during a period of low flow and measuring the

quantity and quality of fine sediment collected.

o Repeat sampling of sediment trapped in the periphyton mat upstream and

downstream of the discharge and during a period of low and high background SIN

concentrations. Use a longer period of time for extraction from sediments e.g. 4 hours

to better estimate total amount of P able to be delivered.

o Run an experiment to estimate the daily dissolved P flux from the sediments as a result

of diurnal pH increases (i.e. mg P/m2/day) (i.e. a time series of pH adjustment

experiment).



6 Change in dissolved phosphorus fraction due to storage and

mixing of effluent with river water

6.1 Introduction

Hamill (2012) found that during periods of low flow (< half median flow) there was more dissolved

phosphorus and dissolved aluminium in the downstream river water than could be explained by the

WWTP discharge but total phosphorus (TP) concentrations in the river water reduced as would be

expected due to dilution of the effluent. One process that might explain this is that after the effluent

enters the river some of the particulate phosphorus bound to alum dissociates to a dissolved form due

to the elevated pH of the river. The effectiveness of aluminium hydroxides (i.e. alum) and iron (III) at

adsorbing P is controlled by pH; optimum absorption at about pH 6.5, and as pH decreases below 6 or

increases above 8 soluble intermediary compounds become more dominate and bound P is released

(Malecki-Brown et al. 2007, Ebeling et al. 2003).

There is also the possibility that the fraction of dissolved phosphorus in effluent samples changed

within the bottles between sampling and analysis. Discrepancies have been observed in DRP data from

samples collected from the same sites, on the same day, analysed using the same methods but by

different laboratories after different time periods. This chapter discusses the results of two simple

experiments investigating how the fraction of dissolved phosphorus in effluent samples is influenced by

pH changes on mixing with river water and by the time between sampling and laboratory analysis.

6.2 Method

6.2.1 Effect of mixing with river water and pH increases

The effect of pH changes due to mixing with river water on the fraction of dissolved phosphorus was

tested for effluent and river water samples.

Samples were collected from the Manawatu River 800m upstream, 800m downstream and from the

WWTP effluent (post wetland) on three occasions during a period of low flow when the WWTP was

dosing effluent with alum to remove DRP, i.e. 11 December 2012, 9 January 2013, and 15 March 2013.

In the laboratory the effluent samples were diluted by mixing effluent and river water at a ratio of

1:100 by volume. Subsamples were collected and the pH adjusted to 7.0, 8.5, 8.8, 9.0 and 9.5. These

were allowed to sit for 20 minutes23 before raw samples and pH-adjusted samples were analysed for

the following variables: total phosphorus (TP), total dissolved phosphorus (TDP), dissolved reactive

phosphorus (DRP), total aluminium (Al), dissolved aluminium, pH, and electrical conductivity (EC).

Laboratory analysis methods and detection limits are show in Table 6.1. All data were reported and

analysed as raw results without censoring even if below the detection limit.

23

This is about the time it takes for effluent to travel to the 800m downstream sample site.



Table 6.1: CEL laboratory methods and detection limits

6.2.2 Effect of time

The effect of storage time in sample bottles on the fraction of dissolved phosphorus was tested using

effluent and river water samples.

Samples were collected from the Manawatu River 800m upstream, 800m downstream and from the

WWTP effluent (post wetland) on two occasions during a period of low flow when the WWTP was

dosing effluent with alum to remove DRP, i.e. 11 December 2012 and 9 January 2013.

Samples were collected in order upstream to downstream and time of collection was noted on the field

sheet. All samples were stored in a cool, dark chilli-bin and taken to CEL laboratory within an hour. At

the laboratory samples were stored in the chilli-bin filtered (0.45 micron) prior to analysis and sub-

sampled as follows:

Within one hour of sample collection;

Six hours after sample collection (stored in chilli-bin);

12 hours after sample collection;

24 hours after sample collection.

Samples were analysed for: total phosphorus, total dissolved phosphorus, dissolved reactive

phosphorus, total aluminium, dissolved aluminium, pH, and electrical conductivity. Laboratory analysis

methods and detection limits are show in Table 6.1.


6.3.1 Effect of changing pH

The effect of manipulating the pH of mixed effluent/river samples differed between samples and

indicated a complex chemistry influencing the transformation and precipitation of river phosphorus and

variable Lab method Detection limit

pH pH

dissolved Aluminium Aluminium - Dissolved 0.016 mg/L

total Aluminium Aluminium - Total 0.016 mg/L

dissolved iron Iron - Dissolved 0.002 mg/L

Total iron Iron - Total 0.002 mg/L

Total ammoniacal nitrogen Nitrogen - Ammonia (colorimetric) 0.005 mg/L

nitrate Nitrite - Ion Chromatography CS 0.005 mg/L

nitrite Nitrate - Ion Chromatography CS 0.005 mg/L

Dissolved oxygen Oxygen - Dissolved Electrode 1 mg/L

Dissolved reactive phosphorus Phosphorus - Dissolved Reactive (colorimetric) 0.002 mg/L

Total dissolved phosphorus Phosphorus - Total Dissolved (colorimetric) 0.01 mg/L

Total phosphorus Phosphorus - Total (colorimetric) 0.01 mg/L



aluminium. Samples from December 2012 and January 2013 showed an increase in DRP, total dissolved

P and dissolved aluminium (Al) as the pH of the mixture was increased. The sample from March showed

a more complex interaction, with an initial increase in DRP from pH 7.8 to 8.0, followed by a decline as

pH was further increased (see Figure 6.1 and 6.2). The concentration of total phosphorus should have,

theoretically, remained constant for different pH treatments but instead declined with increasing pH

(Figure 6.3). Total Al showed a similar pattern to TP, but was more consistent for the March samples.

Some of the differences between samples may be explained by differences in the concentration of

particulate P in the effluent, which was 1, 0.6 and 0.5 mg/L in samples from December, January and

March respectively. More particulate P in the unadjusted sample from January gave greater

opportunity for releasing some as dissolved P as pH increased. There may also be competing

interactions for dissolved phosphorus between different elements. A dominance of calcium-bound

phosphorus after mixing with river water might explain why DRP in the March sample decline as pH

was increased.

Simply mixing the effluent with river water appeared to cause changes in the form of phosphorus. For

the March sample, the DRP of the laboratory-mixed sample was 0.0046 mg/L while DRP in the river and

effluent were 0.0087 and 0.0089 mg/L respectively. In contrast total dissolved P increased with mixing

i.e. 0.02 mg/L in the mixed sample compared to 0.013 mg/L and 0.014 mg/L in the river and effluent

respectively.

The concentrations of DRP and dissolved Al in mixed samples from January and March were very low

and close to the detection limit of 0.002 mg/L and 0.016 mg/L respectively. Analytical results have

considerably more error at low concentrations, and some caution is needed in using the results from

January and March. Ideally the samples should have had less dilution. A 100:1 dilution was

characteristic of actual dilution of the effluent in the river during December, but during January and

March the river provided less than 30 times dilution.

Despite the complex nature of some of the results this work indicates that under some situations

mixing of treated effluent with river water of higher pH would cause release of dissolved phosphorus

from the particulate P in the effluent. This is likely to be most apparent when particulate P in the

effluent is high and dilution with the river is low. Under low flow conditions the pH of the Manawatu

River varies diurnally from about 7.1 to over 8.7. The December samples found that increasing the pH

of the mixture from 7.2 to 8.7 caused a 50% increase in DRP concentration and a 60% increase in TDP

concentration (see Figure 6.1).

This is consistent with results of modelling the water quality effects of the effluent using the Biowin

model (MWH 2013). MWH (2013) applied the Biowin model to assess the effect of the discharge on

DRP concentrations under conditions of diurnally fluctuating river pH. The results showed diurnal

fluctuations in DRP downstream of the discharge as some particulate phosphorus becomes soluble with

diurnal increases in pH. The effect was more apparent when there is less dilution, large pH fluctuations

(i.e. low river flow) and high particulate P in the discharge.



Figure 6.1: Change in DRP due to pH in effluent diluted 100:1 with river water. Particulate P in the

effluent was 1 mg/L, 0.6 mg/L and 0.5 mg/L in samples from December, January and March

respectively.

Figure 6.2: Change in dissolved aluminium due to pH in the effluent diluted 100:1 with river water.

0.000

0.005

0.010

0.015

0.020

0.025

0.030

7.00 7.50 8.00 8.50 9.00 9.50 10.00

DR

P (

mg/

L)

pH (100:1 river to effluent mix)

December

January

March

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

7.00 7.50 8.00 8.50 9.00 9.50 10.00

Dis

solv

ed A

l (m

g/L)


December

January

March



Figure 6.3: Change in total phosphorus due to pH in the effluent diluted 100:1 with river water.

6.3.2 Changes within bottles over time

Samples were collected in December and January to assess the effect of delays in sample analysis on

analytical measurements of DRP. DRP results from treated effluent samples were lowest in samples

analysed within about 1 hour and generally increased as the storage time increased (Table 6.2, Figure

6.4). The DRP in effluent samples analysed after about 24 hours was 71-78% higher than in samples

analysed within an hour (Figure 6.5).

A similar pattern was observed for total dissolved P and dissolved Al, with a higher concentration found

in samples analysed after a longer period of samples being stored in the bottles (Figure 6.6). As

expected the concentration of TP and total Al remained relatively constant (Table 6.2).

The effect of delayed analysis was much more apparent in effluent samples compared to river water

samples (Figure 6.5), and the variability seen in upstream samples probably reflects the variability due

to values being close to analytical detection limits.

Delays in analysis of effluent samples were positively correlated with pH changes in the bottles (Figure

6.7), and small increases in pH (i.e. 0.4 units) are likely to be driving the increases in dissolved P and

dissolved Al.

The results suggest that the chemistry of discharged effluent is relatively unstable and phosphorus

readily shifts from a particulate form to a dissolved form in response to pH changes in the bottles. One

implication is that samples may need to be filtered in the field in order to obtain accurate results of

dissolved phosphorus from effluent samples.

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

7.00 7.50 8.00 8.50 9.00 9.50 10.00

TP (

mg/

L)


December

January

March



Increases in DRP as a result of storage in the bottles (and corresponding pH increases) may explain the

differences in results observed between 24 hour integrated samples (collected by PNCC) and spot

samples collected on the same day for the joint monitoring programme (see Hamill 2012). The results

from the time integrated sampler were consistently higher than spot samples on the same day.

Additional sampling has not found a diurnal fluctuation in DRP, but the difference is consistent with an

increasing fraction of DRP due to longer delays between collection and analysis.

Table 6.2: Effect of delays in sample analysis on samples collected from the WWTP discharge, the

Manawatu River upstream and the Manawatu River downstream.

Site sample date

Hours

since

sampling

DRP

(mg/L)

TDP

(mg/L)

TP

(mg/L)

Particulate

P (mg/L)

Al Total

(mg/L)

Al

dissolved

EC

(µS/cm) pH DRP:TP

%

change

DRP

%

change

TDP

Downstream 800 m 11-Dec-12 0.95 0.013 0.019 0.032 0.013 0.188 0.017 182 7.51 0.42

Downstream 800 m 11-Dec-12 4.45 0.015 0.022 0.032 0.010 0.170 0.038 177.2 7.51 0.47 13.0 16.7

Downstream 800 m 11-Dec-12 8.45 0.017 0.017 0.022 0.005 0.182 0.037 180.2 7.76 0.78 25.9 -9.1

Downstream 800 m 11-Dec-12 24.95 0.016 0.018 0.031 0.012 0.168 0.040 180.9 7.72 0.53 22.5 -3.2

Upstream 800 m 11-Dec-12 1.25 0.008 0.011 0.022 0.010 0.159 0.014 178.6 7.49 0.36

Upstream 800 m 11-Dec-12 4.75 0.008 0.010 0.019 0.009 0.172 0.015 174.2 7.51 0.41 0.8 -15.3

Upstream 800 m 11-Dec-12 8.75 0.008 0.013 0.019 0.006 0.150 0.023 175.3 7.72 0.42 3.6 15.1

Upstream 800 m 11-Dec-12 25.25 0.009 0.010 0.015 0.005 0.136 0.020 176.4 7.59 0.57 11.5 -10.0

Wetland outfall 11-Dec-12 1.05 0.129 0.206 1.211 1.004 3.406 0.309 693 7.16 0.11

Wetland outfall 11-Dec-12 4.55 0.142 0.215 1.287 1.072 3.230 0.357 689 7.32 0.11 9.9 4.1



Downstream 800 m 9-Jan-13 0.83 0.006 0.010 0.017 0.007 0.087 0.062 203 7.69 0.36

Downstream 800 m 9-Jan-13 4.83 0.008 0.011 0.018 0.007 0.070 0.035 203 7.65 0.46 32.3 10.0

Downstream 800 m 9-Jan-13 6.25 0.008 0.016 0.018 0.002 0.078 0.033 201 7.66 0.44 29.0 60.0

Downstream 800 m 9-Jan-13 23.6 0.009 0.010 0.017 0.007 0.078 0.079 201 7.68 0.50 37.1 0.0

Upstream 800 m 9-Jan-13 1.08 0.005 0.008 0.013 0.005 0.076 0.025 202 7.69 0.35

Upstream 800 m 9-Jan-13 5.08 0.007 0.008 0.016 0.008 0.066 0.014 197 7.5 0.41 41.3 0.0

Upstream 800 m 9-Jan-13 6.5 0.005 0.008 0.013 0.005 0.074 0.029 197.3 7.57 0.36 2.2 0.0

Upstream 800 m 9-Jan-13 23.85 0.005 0.006 0.012 0.006 0.066 0.030 198.7 7.67 0.41 6.5 -25.0

Wetland outfall 9-Jan-13 1 0.051 0.118 0.705 0.587 1.841 0.127 709 7.22 0.07

Wetland outfall 9-Jan-13 5 0.073 0.150 0.684 0.534 1.873 0.164 707 7.28 0.11 44.6 27.1

Wetland outfall 9-Jan-13 6.4 0.068 0.134 0.700 0.566 1.643 0.138 706 7.35 0.10 33.1 13.6

Wetland outfall 9-Jan-13 23.8 0.090 0.158 0.689 0.531 1.745 0.188 704 7.49 0.13 78.3 33.9



Figure 6.4: DRP variation in stored effluent samples due to timing of laboratory analysis.

Figure 6.5: Percent change in DRP due to timing of laboratory analysis in stored effluent samples from

effluent, upstream river samples and downstream river samples.

0.00

0.05

0.10

0.15

0.20

0.25

0 5 10 15 20 25 30

DR

P (

mg/

L)

Hours since sample collection

December

January

0

10

20

30

40

50

60

70

80

90

0 5 10 15 20 25 30

% c

han

ge in

DR

P


effluent Dec

effluent Jan

downstream Jan

downstream Dec

upstream Dec

upstream Jan



Figure 6.6: Dissolved aluminium variation in stored effluent samples due to timing of laboratory

analysis.

Figure 6.7: pH variation in stored effluent samples due to timing of laboratory analysis.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 5 10 15 20 25 30

dis

solv

ed A

l (m

g/L)


December

January

7.0

7.1

7.2

7.3

7.4

7.5

7.6

7.7

0 5 10 15 20 25 30

pH


December

January



6.4 Summary


The effect of manipulating the pH of mixed effluent/river samples differed between samples

and indicated a complex chemistry influencing the dissolving and precipitation of river

phosphorus and aluminium, nevertheless there was a general pattern of an increase in pH

causing an increase in DRP within effluent samples.

The results of the present experiments supported model outputs (MWH 2013) that indicating

during periods of low flow and when the treated effluent has high particulate P, diurnal pH

increases in the river water can release dissolved phosphorus from the particulate P in the

effluent.

The analytical results from analysing samples for dissolved reactive phosphorus from the

WWTP discharge showed considerable variability depending on the number of hours the

sample was in storage prior to analysis.

To improve the accuracy of measurements it is recommended that where appropriate effluent

samples are filtered in the field prior to transporting to the laboratory. It is acknowledged that

field filtering is not always practical; where field filtering of effluent samples do not occur the

samples should be transported and filtered in the laboratory as soon as possible after sampling.



7 Synthesis and Conclusions

Investigations carried out for this report have found that the Manawatu River is a highly complex

natural system with significant changes in nutrient concentrations in the river during periods of

prolonged low flow. This has implications for how wastewater discharges might be treated in order to

minimise effects on periphyton growth.

7.1 Impact of the wastewater discharge

During periods of low river flow (i.e. less than half median flow) the wastewater treatment plant uses

alum treatment to reduce the amount of dissolved phosphorus (DRP) in the discharge to a very low

concentration and occasionally during January 2013 it was not possible to detect any elevation in DRP

due to the discharge. Hamill (2012) found that reducing DRP in the discharge was helping to control

periphyton growth; nevertheless periphyton still grew prolifically downstream of the discharge.

In 2013 the periphyton biomass downstream of the discharge exceeded the 35 g/m2 AFDM guideline

for protection of trout habitat within 15 to 17 days. This stimulatory effect of the discharge on

periphyton growth was most evident at the sample sites with 1.2 km downstream of the discharge and

was considerably less at the sample site 3.8 km downstream (i.e. upstream of Longburn). The smaller

effect observed near Longburn may reflect the assimilation and removal (e.g. by denitrification) of

nutrients by algae and within the riverbed.

The very low DRP concentrations recorded in January 2013 should theoretically have been limiting

periphyton growth, despite high nitrogen concentrations downstream of the discharge. However, the

periphyton grew rapidly and showed little evidence of nutrient limitation. This suggested that the

periphyton was obtaining phosphorus from other sources (e.g. trapped sediments).

7.2 Reasons why periphyton grows fast downstream of the discharge

The investigations identified several reasons explaining rapid periphyton growth downstream of the

discharge, these were:

Particulate P in the discharge released dissolved phosphorus to the river under low flow

conditions when pH in the river has large diurnal fluctuations. The downstream load of DRP was

often higher than could be explained by DRP in the discharge. Experiments found a complex

chemistry influencing the form of phosphorus. Nevertheless, the results supported model

outputs (MWH 2013) that diurnal pH increases in the river water can release dissolved

phosphorus from the particulate P in the effluent, especially when the treated effluent has high

particulate P and during periods of low flow.

Particulate P associated with suspended sediment in the river was trapped within periphyton

mats and released P in direct vicinity to algal cells. An increase in pH was able to release some

dissolved P at both the upstream and downstream sites.

Particulate P released in the discharge was trapped within periphyton mats and released P in

direct vicinity to algal cells. Increases in pH were more effective at releasing dissolved P from

trapped sediments at the downstream site compared to the sediment trapped by periphyton at



the upstream site. At the downstream site, increasing the pH of trapped sediments to 8.5 and

9.5 caused a 102% and 243% increase in DRP respectively; while at the upstream site it caused

no change and a 13% increase respectively. This mechanism for periphyton to obtain P from

sediment is particularly strong downstream of the WWTP discharge, which may be because

some of the trapped sediment is residual alum floc to which P is more weakly bound compared

to river sediments.

There was no evidence that undertaking the alum dosing for a longer period of time with the current

treatment system would reduce downstream periphyton growth; instead:

The initial peak in maximum periphyton biomass occurred progressively earlier for periphyton

trials started later in the summer – suggesting periphyton grew more rapidly rather than more

slowly after longer periods of alum dosing;

Periphyton growth rates measured on concrete tiles early in summer when alum dosing

occurred for short periods were similar to those placed in the river later in the summer after a

longer period of alum dosing;

Long periods of removing DRP from the discharge by alum dosing (e.g. February and March)

had no noticeable effect on downstream periphyton biomass compared to short periods (e.g.

November and December).

These processes for releasing dissolved P were controlled by pH within the river water and periphyton

mats. Daily increases in pH are caused by the periphyton itself, and thus the effect of these processes is

most apparent during periods of low river flow, when periphyton biomass is high, and within the

periphyton mat (i.e. measured up to pH 9.6). The periphyton downstream of the discharge was ‘hungry’

for P with lower concentrations close to the mat compared to overlying water.

The potential supply of P increases as periphyton biomass increases because more inorganic sediment

is trapped in periphyton mats. There was also evidence that more fine sediment was trapped in

periphyton mats downstream of the WWTP.

During the summer the potential limiting nutrient upstream of the discharge changed from P limitation

to N limitation. This switch to nitrogen limitation occurred after an extended period of low flow (i.e.

river flow < 20-30 m3/s) due to a drop in the background concentration of dissolved inorganic nitrogen

(SIN) in the Manawatu River.

Furthermore as the flow continued to drop to below 20 m3/s; the dissolved P in the river increased to

above the summer median – further reducing the potential for P to limit periphyton growth. This

increase in dissolved P may have been caused by the combined effects of P released from river

sediment trapped within the periphyton mat and a mature periphyton community with less net growth,

more senescence and less net demand for nutrients.

Nitrogen limitation was confirmed by periphyton nutrient bioassays during February-March 2013.

These indicated that periphyton in the Manawatu River upstream of the WWTP discharge was primarily

limited by nitrogen with secondary phosphorus limitation. Periphyton growth in the river downstream

of the WWTP showed a small amount of dual limitation by N+P.



Despite high concentrations of SIN in the river downstream of the discharge, the P treatment did not

stimulate periphyton growth compared to that on the control and N treatments – adding weight to

evidence that periphyton was extracting P from sediments trapped within their mat.

The nitrogen limitation found in 2013 contrasted with results from April 2012 which found possible

phosphorus limitation. These different results are consistent with the different river flow conditions

and background concentrations of N and P in the river during the wet summer of 2011-12 and the

drought of 2012-13.

7.3 Implications for the WWTP discharge

These findings have significant implications for how to best treat the wastewater that is discharged into the

river. Effluent treatment approaches that could be taken to help limit excessive periphyton growth include:

Reducing dissolved phosphorus concentrations (as is currently done);

Reducing particulate phosphorus (P) concentration in the discharge in addition to the dissolved P;

and

Reducing soluble inorganic nitrogen (SIN) concentration when river flow is very low (e.g. <20-30

m3/s).

River are complex and even if these actions are taken it is possible that periphyton will grow more quickly

downstream of the WWTP discharge compared to upstream, however the rate of growth and the period of

time guidelines values are exceeded will reduce.

7.4 Complex river dynamics

A number of findings highlighted the complex dynamics occurring in the Manawatu River and

emphasises the need for site specific information when establishing resource consent conditions, these

included:

Estimates of periphyton biomass downstream of the WWTP discharge differed depending on the

method used. Chlorophyll a appeared to over-estimate periphyton biomass at the downstream

sites and AFDM over-estimated periphyton biomass at the upstream site. For sites downstream of

the discharge, AFDM is a better measure for assessing periphyton cover against guideline values

because the AFDM guideline value of 35 mg /m2 corresponds to a decline in mayfly abundance in

the river (as reported in Hamill 2012). Percent cover (e.g. weighted composite cover) provides

complementary information that helps confirm biomass measures.

There was evidence that some characteristics of the sewage stimulated periphyton growth in

addition to the N and P; however the effect was small compared to the combined effect of N and P

stimulating periphyton growth and of little practical consequence.

Grazing by macroinvertebrates appeared to play an important role in controlling periphyton

biomass at the upstream site. This was highlighted by the periphyton accumulation on substrates

that resisted the effects of periphyton grazing.



Measurement of dissolved reactive phosphorus differed depending on how long samples were

stored prior to analysis. Filtering the samples in the field would ensure more accurate and

consistent results. However it is acknowledged that field filtering is not always practical; where field

filtering of effluent samples do not occur the samples should be transported and filtered in the

laboratory as soon as possible after sampling.

7.5 Further investigations

This report has taken a weight of evidence approach to understand river processes causing excessive

periphyton growth downstream of the WWTP discharge. While the studies provide confidence to make

recommendations regarding upgrades to the WWTP discharge quality, a number of additional

investigations have been identified that would improve understanding of the periphyton dynamics,

these might include:

Estimate the rate at which periphyton accumulates fine sediment at sites upstream and

downstream of the WWTP discharge. This could be done by installing sediment traps (e.g.

Astroturf matting) in the river during a period of low flow and measuring the quantity and

quality of fine sediment collected. This would help establish the extent to which a rain of

sediments provide a continual source of P and help confirm evidence of more fine sediment

settling downstream of the WWTP as a result of alum floc.

Estimate the total amount of P able to be delivered by trapped sediment. This could be done by

sampling of sediment trapped in the periphyton mat upstream and downstream of the

discharge and extracting P using a time series of pH adjustments, repeated over multiple time

periods.

Estimate the daily flux (i.e. mg P/m2/day) of dissolved N and P from sediment trapped in

periphyton mats due to diurnal pH increases (i.e. light + dark conditions). An experiment could

place cobbles covered in periphyton in benthic chambers within the river to measure changes

in N, P, dissolved oxygen and pH. Paired chambers could test P uptake from the water by

periphyton with and without sediment trapped in the mat, as well as testing the effect of

different types of sediment quality. Periphyton obtaining P from sediments would use less P

from the water.

Better understand the cause of late summer increase in DRP within the river by regular

sampling of pH and nutrients at the periphyton interface and overlying river water throughout

a summer period covering a periphyton accrual phase and a loss phase.

Undertake specific sampling to assess the ratio of chlorophyll a to AFDM of specific periphyton

species common in the Manawatu River e.g. Stigeoclonium sp., Cladophora sp., Phormidium sp.



References

Afsar, M.Z., Hoque, S., Osman K.T. 2012. Phosphate Desorption Characteristics of Some Representative

Soils of Bangladesh: Effect of Exchangeable Anions, Water Molecules and Solution to Soil Ratios.

Open Journal of Soil Science, 2012(2): 234-241.

ANZECC 2000. Australian and New Zealand Guidelines for Fresh and Marine Waters. National Water

Quality Management Strategy, Australian and New Zealand Environmental and Conservation

Council.

Biggs, B.J.F. 1990: Use of relative specific growth rates of periphytic diatoms to assess enrichment of a

stream. New Zealand Journal of Marine and Freshwater Research 24: 9–18.

Biggs, B.J.F 2000. NZ Periphyton Guideline: Detecting, Monitoring and Managing Enrichment of

Streams. Prepared for the Ministry for the Environment.

Biggs, B.J.F., Kelly D.J. 2002. The relationship between dissolved nutrients and periphyton biomass in the

Manawatu River downstream of the Palmerston North City Council domestic waste discharge.

Prepared for horizons MW. NIWA Client Report: CHC02/08.

Biggs, B.J.F., Kilroy, K.C. 2000. Stream periphyton monitoring manual. Ministry for the Environment,

Wellington.

Bothwell, M.L. 1988. Growth rate responses of lotic periphytic diatoms to experimental phosphorus

enrichment: the influence of temperature and light. Canadian Journal of Fisheries and Aquatic

Sciences 45: 261–270.

Bothwell, M.L. 1989. Phosphorus-limited growth dynamics of lotic periphytic diatom communities:

Areal biomass and cellular growth rate response. Canadian Journal of Fisheries and Aquatic Sciences

46:1293-1301

Cameron D. 2002. Statement of evidence of David James Cameron. In the matter of the applications of

the Palmerston North City Council for resource consents for its wastewater scheme.

Cameron, D. 2011. A benthic biota survey of the Manawatu River at Palmerston North. Prepared by

MWH for Palmerston North City Council. February 2011.

Davies-Colley, R.J.; Hickey, C.W.; Quinn, J.M.; Ryan, P.A. 1992. Effects of clay discharges on streams. 1.

Optical properties and epilithon. Hydrobiologia 248: 215–234.

Ebeling J.M., Sibrell P.L., Ogden S.R., Summerfelt S.T. 2003. Evaluation of chemical coagulation-

flocculation aids for the removal of suspended solids and phosphorus from intensive recirculating

aquaculture effluent discharge. Aquacult. Eng. 29:23–42.

USEPA 2009. Draft 2009. Update aquatic life ambient water quality criteria for ammonia – freshwater.

EPA-822-D-09-001. Environmental Protection Agency, United States.



Hamill, K.D. 2012. Effects of Palmerston North City’s Wastewater Treatment Plant discharge on water

quality and aquatic life in the Manawatu River: Joint monitoring programme between Palmerston

North City Council and Horizons Regional Council. Prepared for Palmerston North City Council and

Horizons Regional Council by Opus International Consultants.

Harding JS, Clapcott JE, Quinn JM, Hayes JW, Joy MK, Storey RG, Greig HS, Hay J, James T, Beech MA,

Ozane R, Meredith AS, Boothroyd IKG 2009. Stream habitat assessment protocols for wadeable

rivers and streams of New Zealand. Christchurch, University of Canterbury.

Heckey, R.E., Kilham P. 1988. Nutrient limitation of phytoplankton in freshwater and marine

environments: A review of recent evidence of the effects of enrichment. Limnology and

Oceanography 1988: 796-822.

Hedley MJ 1978. Assessment of the biological availability of particulate-phase phosphorus. Unpublished

PhD thesis. Massey University, Palmerston North.

Horner, R.R., Welch, E.B., Seeley, M.R., Jacoby J.J. 1990. Responses of periphyton to changes in current

velocity, suspended sediment and phosphorus concentration. Freshwater Biology 24: 215-232.

Jernakoff P., Nielsen J. 1997. The relative importance of amphipod and gastropod grazers in Posidonia

sinuosa meadows. Aquatic Botany 56 (1997): 183 -202.

Kilroy, C. Biggs, B., Death, R. 2008. A periphyton monitoring plan for the Manawatu-Wanganui Region.

NIWA client report: CHC2008-03.

Kilroy, C. 2012. Periphyton in the Manawatu-Whanganui region: review of three years of monitoring.

Prepared for Horizons Regional Council by NIWA. Horizons Report No. 2012/EXT/1276

Malecki-Brown L., White JR, Reddy KR 2007. Soil Biogeochemical Characteristics Influenced by Alum

Application in a Municipal Wastewater Treatment Wetland. Journal of Environmental Quality 36:

1904–1913

Matheson, F., Quinn J., Hickey C. 2012. Review of the New Zealand instream plant and nutrient

guidelines and development of an extended decision making framework: Phases 1 and 2 final

report. Prepared for the Ministry of Science and Innovation EnviroLink Fund. August 2012. NIWA

Client Report HAM2012-018.

McArthur, K.J., Roygard R., Clark M. 2010. Understanding variations in the limiting nitrogen and

phosphorus status of rivers in the Manawatu-Wanganui Region, New Zealand. Journal of Hydrology

49 (1): 15-33.

McDowell R.W., Wilcock R.J. 2007. Sources of sediment and phosphorus in stream flow of a highly

productive dairy farmed catchment. Journal of Environmental Quality 36: 540–548.

McIntire C.D., Phinney H.K. 1965. Laboratory Studies of Periphyton Production and Community

Metabolism in Lotic Environments. Ecological Monographs, 35 (3): 237-258

Meeks J. C. 1974. Chlorophylls. Pp. 161-75 in W. D. P. Stewart (ed.) "Algal Physiology and Biochemistry".

Blackwell, London. 989 pp.



Menendez M., Harrera J., Comin F.A. 2002. Effect of nitrogen and phosphorus supply on growth,

chlorophyll content and tissue composition of the macroalga Chaetomorpha linum (O.F. Mull.) Kutz

in a Mediterranean coastal lagoon. Scientia Marina 66(4):355-364.

MWH 2013. Totara Road Wastewater Treatment Plant upgrade options technical report. Wastewater

Discharge Consent Review. Prepared for Palmerston North City Council by MWH, July 2013.

Parfitt R., Dymond J., Ausseil A.; Clothier, B.; Deurer, M.; Gillingham, A.; Gray, R.; Houlbrooke, D.;

Mackay, A.; McDowell, R. 2007. Best Practice Phosphorus Losses from Agricultural Land. Prepared

for Horizons Regional Council. Landcare Research Contract Report No. LC0708/012.

Rutherford, J.C., Ovenden R., Nagels J.W. 1997. Low flow mixing measurements in the Manawatu River.

NIWA Consultancy Report PNC60201/3. Prepared for Palmerston North City Council.

Stark, J.D. 1985: A macroinvertebrate community index of water quality for stony streams. Water and

Soil Miscellaneous Publication 87.

Stark, J.D. 1998. SQMCI: A biotic index for freshwater macroinvertebrate coded abundance data. New

Zealand Journal of Marine and Freshwater Research 32: 55-66.

Stark, JD; Boothroyd, IKG; Harding JS; Maxted, JR; Scarsbrook, MR 2001. Protocols for sampling

macroinvertebrates in wadeable streams. New Zealand Macroinvertebrate Working Group Report

no. 1. Prepared for the Ministry for the Environment. Sustainable Management Fund Project No.

5103. 57p.

Stich H.B., Brinker A. 2005. Less is better: Uncorrrected versus pheopigment-corrected photometric

chlorophyll-a estimation. Arch. Hydrobiol. 162 (1): 111-120

Stutter MI, Demars BOL, Langan SJ 2010. River phosphorus cycling: Separating biotic and abiotic uptake

during short-term changes in sewage effluent loading. Water Research 44: 4425 -4436.

White E, Payne GW 1977. Chlorophyll production, in response to nutrient additions, by the algae in

Lake Taupo water. New Zealand Journal of Marine and Freshwater Research, 11(3): 501-507.



Appendix 1: Water quality results for summer 2012/2013

Site 1 Date

Flow

(m3/s)

Discharge

eff (m3/s)

Temperature

(oC)

DO

(g/m3)

pH

(lab/field)

Field EC

(uS/cm)

DRP HRC

(g/m3)

TDP

(g/m3)

TP

(g/m3)

TN

(g/m3)

SIN

(g/m3)

NH4-N

(g/m3)

NNN

(g/m3)

Turbidity

EPA

(NTU)

E. coli

(MPN/100mL)

Chl a

(mg/m2)

Phe

(mg/m2)

PeriWCC

(%)

Manawatu d/s 31/10/2012 8:30 46.8 16.2 8 201 0.033 0.037 0.064 0.931 0.7114 0.195 0.5164 118 17.9 8.0 6.6

Manawatu d/s 7/11/2012 10:05 38.4 13.9 10.47 7.97 212.5 0.016 0.019 0.027 0.895 0.7572 0.312 0.4452 12 132.7 69.4 18.2

Manawatu d/s 14/11/2012 13:00 37.9 14.4 12.29 8.54 202.6 0.019 0.013 0.039 0.758 0.6817 0.32 0.3617 2.71 953 243.8 202.8 48.9

Manawatu d/s 14/11/2012 14:24 37.7 14.6 12.13 8.37 234.3 0.026 0.024 0.047 0.884 0.7356 0.424 0.3116 38

Manawatu d/s 21/11/2012 10:02 38.2 16.3 9.97 7.88 190.6 0.005 0.023 0.052 0.832 0.3985 0.168 0.2305 3.01 70 147.9 93.6 20.3

Manawatu d/s 28/11/2012 8:37 24.6 17.2 9.12 7.66 228.6 0.018 0.033 0.825 0.6299 0.361 0.2689 2.04 64 205.0 33.8 10.6

Manawatu d/s 5/12/2012 13:25 25.6 19.6 11.27 8.1 207.8 0.019 0.027 0.04 0.941 0.8413 0.634 0.2073 1.08 39 178.0 74.7 22.0

Manawatu d/s 12/12/2012 7:11 27.0 16.9 9.28 7.7 193.6 0.014 0.018 0.026 0.633 0.416 0.197 0.219 1.72 49 80.4 19.4 23.6

Manawatu d/s 12/12/2012 10:00 26.5 18.1 10.31 7.84 199.1 0.006 0.01 0.024 0.528 0.4838 0.093 0.3908 5.19 63

Manawatu d/s 20/12/2012 7:09 76.6 17.7 8.56 7.47 107.9 0.019 0.021 0.045 0.421 0.2735 0.112 0.1615 29.3 582 2.1 0.7

Manawatu d/s 28/12/2012 12:06 77.9 18.4 8.87 7.8 151.3 0.029 0.033 0.102 0.747 0.41 0.195 0.215 13.3 447 139.5 3.4

Manawatu d/s 3/01/2013 9:10 43.4 18 8.52 7.66 167.7 0.017 0.017 0.026 0.761 0.4616 0.344 0.1176 3.53 265 65.4 11.6 18.4

Manawatu d/s 9/01/2013 8:42 23.7 16.8 8.5 7.63 205.7 0.003 0.013 0.02 0.539 0.3027 0.218 0.0847 1.48 53 229.9 117.4 42.8

Manawatu d/s 16/01/2013 7:26 40.1 18.7 8.1 7.49 140.6 0.0002 0.01 0.018 0.615 0.3888 0.238 0.1508 7.06 222 20.0

Manawatu d/s 16/01/2013 9:55 40.2 19.2 9.25 7.67 150.2 0.0002 0.009 0.012 0.535 0.2855 0.136 0.1495 5.53 138 262.6 112.5

Manawatu d/s 23/01/2013 8:00 21.8 20.8 7.64 7.6 185.1 0.005 0.008 0.012 0.45 0.2422 0.202 0.0402 1.16 16 515.2 57.3 55.3

Manawatu d/s 30/01/2013 8:00 13.8 20.4 8.11 7.8 225.7 0.006 0.011 0.022 0.583 0.3266 0.276 0.0506 1.43 8 885.1 105.2 53.2

Manawatu d/s 4/02/2013 14:47 13.0 22.5 8.13 8 292.7 0.005 0.029 0.039 1.186 0.7897 0.691 0.0987 0.92 6212

Manawatu d/s 7/02/2013 7:50 38.2 16 9.36 7.66 173.7 0.012 0.019 0.036 0.576 0.2992 0.1 0.1992 5.77 373 39.3 1.7

Manawatu d/s 13/02/2013 6:23 14.5 20 7.47 7.51 226.9 0.019 0.018 0.032 0.7 0.5315 0.464 0.0675 1.92 80 430.2 38.5 39.4

Manawatu d/s 18/02/2013 14:14 12.1 21.9 10.43 8.1 250.6 0.03 0.036 0.047 1.269 1.0806 0.943 0.1376 1.29 25

Manawatu d/s 19/02/2013 8:05 11.8 19.9 8 258 0.03 0.041 0.033 0.797 0.5468 0.484 0.0628 1.34 21

Manawatu d/s 20/02/2013 7:35 11.6 20.5 7.33 7.6 245.3 0.019 0.019 0.026 0.689 0.5345 0.473 0.0615 0.73 25 212.0 32.3 52.2

Manawatu d/s 21/02/2013 12:56 11.3 22.3 8.1 249 0.022 0.027 0.035 1.15 0.8641 0.768 0.0961 1.18 30

Manawatu d/s 22/02/2013 14:48 10.9 21.3 10.24 8.1 304.9 0.029 0.031 0.04 1.22 0.9135 0.822 0.0915 0.68 118

Manawatu d/s 26/02/2013 14:02 10.5 21.3 8 261 0.033 0.037 0.048 1.553 1.28 1.168 0.112 0.73 28

Manawatu d/s 27/02/2013 7:51 10.3 19.9 9.08 7.57 263.2 0.019 0.017 0.023 0.707 0.5629 0.495 0.0679 1.24 21 309.2 5.2 34.3

Manawatu d/s 27/02/2013 10:10 10.3 21.4 11.96 8.49 256.4 0.007 0.01 0.025 0.769 0.2676 0.197 0.0706 1.16 4

Manawatu d/s 28/02/2013 6:26 10.1 19.4 7.16 7.7 267.3 0.025 0.04 0.724 37.501 0.7195 0.64 0.0795 0.81 21

Manawatu d/s 1/03/2013 12:00 10.1 21.7 9.56 8 267.9 0.006 0.016 0.029 1.184 0.7805 0.748 0.0325 0.75 21

Manawatu d/s 5/03/2013 13:55 10.0 19.8 10.64 8.1 274.6 0.036 0.036 0.047 1.48 1.1667 1.106 0.0607 0.71 25

Manawatu d/s 6/03/2013 8:12 10.3 17.6 8 7.8 268.9 0.023 0.023 0.035 1.008 0.766 0.685 0.081 0.68 30 307.7 52.2 41.7

Manawatu d/s 8/03/2013 13:56 10.1 21.4 10.72 8.1 276 0.025 0.027 0.033 1.511 1.1166 1.069 0.0476 0.65 21

Manawatu d/s 11/03/2013 10:15 9.6 19.6 9.51 8 271.3 0.018 0.017 0.027 1.033 0.683 0.622 0.061 0.81 8

Manawatu d/s 13/03/2013 10:55 9.3 18.4 9.97 8.27 270.4 0.016 0.019 0.028 0.858 0.5425 0.5 0.0425 1.34 21

Manawatu d/s 14/03/2013 7:40 9.2 17.6 7.9 258 0.016 0.014 0.027 0.959 0.6791 0.621 0.0581 0.85 30 397.2 4.2 43.4

Manawatu d/s 20/03/2013 7:03 73.5 15.3 8.61 7.6 159.4 0.024 0.022 0.086 0.91 0.4539 0.127 0.3269 39.7 2634

Manawatu d/s 27/03/2013 7:46 12.5 17.6 7.95 7.3 233.6 0.024 0.021 0.031 0.753 0.5273 0.501 0.0263 1.36 176 188.0 0.0 12.4

Manawatu d/s 3/04/2013 8:14 7.7 266 0.02 0.022 0.024 0.739 0.5339 0.472 0.0619 1.02 146 207.2 35.8 28.8

Manawatu d/s 10/04/2013 14:23 8.2 217.6 0.015 0.542 0.542 3.29 593.2 228.9 57.7 26.8

Manawatu d/s 16/04/2013 209.6 63.8 12.9

Manawatu d/s 1/05/2013 8.8 0.9 0.0



Site 1 Date

Flow

(m3/s)

Discharge

eff (m3/s)

Temperature

(oC)

DO

(g/m3)

pH

(lab/field)

Field EC

(uS/cm)

DRP HRC

(g/m3)

TDP

(g/m3)

TP

(g/m3)

TN

(g/m3)

SIN

(g/m3)

NH4-N

(g/m3)

NNN

(g/m3)

Turbidity

EPA

(NTU)

E. coli

(MPN/100mL)

Chl a

(mg/m2)

Phe

(mg/m2)

PeriWCC

(%)

Manawatu u/s 31/10/2012 7:41 47.0 16.1 7.9 198 0.014 0.015 0.024 0.665 0.5193 0.002 0.5173 64 1.9 0.3 10.0

Manawatu u/s 7/11/2012 9:09 38.6 13.6 9.94 7.88 207.1 0.01 0.013 0.017 0.544 0.4371 0.0001 0.4371 93 7.7 2.1 5.4

Manawatu u/s 14/11/2012 12:35 37.9 14.7 11.44 8.29 195.4 0.007 0.006 0.017 0.379 0.3121 0.0001 0.3121 3.29 39 10.7 2.5 5.8

Manawatu u/s 14/11/2012 13:26 37.9 14.4 11.58 8.3 193.6 0.007 0.007 0.015 0.376 0.2951 0.001 0.2941 30

Manawatu u/s 21/11/2012 9:26 38.5 16.1 10.05 7.89 184.7 0.005 0.01 0.025 0.47 0.1729 0.002 0.1709 3.14 92 15.5 4.0 6.9

Manawatu u/s 28/11/2012 7:45 25.0 17.2 8.99 7.7 263 0.007 0.022 0.441 0.2334 0.001 0.2324 1.86 29 34.4 6.2 10.7

Manawatu u/s 5/12/2012 14:05 25.5 19.6 11.36 8.3 197.7 0.005 0.013 0.016 0.206 0.2041 0.052 0.1521 1.16 34 111.7 18.5 13.0

Manawatu u/s 12/12/2012 8:07 26.8 16.9 10.02 7.8 189.1 0.009 0.013 0.017 0.343 0.1478 0.007 0.1408 1.69 39 53.5 7.3 8.3

Manawatu u/s 12/12/2012 9:30 26.6 17.7 10.98 7.92 193.4 0.005 0.008 0.017 0.313 0.1104 0.0001 0.1104 1.62 16

Manawatu u/s 20/12/2012 7:45 74.1 17.8 8.53 7.45 108.2 0.011 0.013 0.043 0.3 0.1413 0.014 0.1273 26.3 524 16.7 1.4

Manawatu u/s 28/12/2012 12:48 76.7 18.4 8.92 7.8 149.5 0.018 0.022 0.049 0.459 0.1584 0.016 0.1424 10.1 576 24.5 5.7

Manawatu u/s 3/01/2013 7:43 43.0 17.9 8.44 7.59 162.7 0.016 0.021 0.021 0.383 0.1509 0.007 0.1439 3.86 208 25.3 9.9 8.5

Manawatu u/s 9/01/2013 9:31 23.7 16.8 8.95 7.72 201 0.003 0.007 0.015 0.209 0.0505 0.0001 0.0505 1.78 61 88.9 29.1 9.5

Manawatu u/s 16/01/2013 8:35 40.5 18.9 8.54 7.71 136.8 0.0002 0.008 0.011 0.282 0.0966 0.003 0.0936 6.96 154 52.5 29.1 21.3

Manawatu u/s 16/01/2013 9:35 40.5 19 9.08 7.89 141.5 0.0002 0.008 0.007 0.249 0.0652 0.0001 0.0652 5.68 158

Manawatu u/s 23/01/2013 8:55 21.8 21.7 8.93 7.84 181.6 0.007 0.009 0.01 0.145 0.005 0.001 0.004 1.39 4 36.6 13.2 35.6

Manawatu u/s 30/01/2013 8:50 13.7 20.7 8.52 7.86 220.6 0.007 0.01 0.017 0.176 0.0022 0.001 0.0012 1.28 8 19.4 16.0 45.0

Manawatu u/s 4/02/2013 15:38 13.2 22.5 8.61 8.1 67 0.01 0.014 0.02 0.207 0.0002 0.0001 0 1.34 2908

Manawatu u/s 7/02/2013 8:20 37.8 16.2 9.55 7.81 171.5 0.01 0.014 0.03 0.416 0.1757 0.0001 0.1757 3.66 310 8.2 1.5

Manawatu u/s 13/02/2013 7:11 14.5 19.6 7.93 7.63 220.5 0.011 0.01 0.019 0.163 0.0002 0.0001 0 1.67 34 61.4 10.5 13.2

Manawatu u/s 18/02/2013 14:47 12.1 22.6 10.62 8.2 281.6 0.012 0.013 0.022 0.162 0.002 0.002 0 1.53 21

Manawatu u/s 19/02/2013 8:50 11.8 19.9 8 249 0.013 0.016 0.019 0.168 0.0002 0.0001 0 1.21 25

Manawatu u/s 20/02/2013 8:33 11.6 20.4 8.27 7.78 234.8 0.012 0.013 0.016 0.157 0.0048 0.001 0.0038 0.87 21 26.2 6.6 18.7

Manawatu u/s 21/02/2013 12:46 11.3 22.4 8.2 234 0.01 0.011 0.016 0.173 0.002 0.0001 0.002 1.14 16

Manawatu u/s 22/02/2013 14:08 10.9 21.4 10.42 8.2 285.9 0.012 0.012 0.016 0.159 0.002 0.0001 0.002 0.64 281

Manawatu u/s 26/02/2013 15:00 10.5 27.9 8.3 243 0.012 0.015 0.019 0.182 0.0045 0.0001 0.0045 0.72 12

Manawatu u/s 27/02/2013 8:42 10.3 20.2 9.96 7.75 254.4 0.013 0.013 0.016 0.15 0.0106 0.007 0.0036 1.55 12 15.8 4.9 22.5

Manawatu u/s 27/02/2013 9:47 10.3 20.6 9.5 7.89 255.3 0.013 0.012 0.018 0.152 0.0083 0.003 0.0053 2.53 44

Manawatu u/s 28/02/2013 6:50 10.1 19.2 7.59 7.8 255.2 0.014 0.013 0.016 0.167 0.0022 0.0001 0.0022 0.74 8

Manawatu u/s 1/03/2013 13:10 10.1 22.8 9.8 8.2 252.6 0.012 0.014 0.015 0.142 0.0008 0.0001 0.0008 0.63 21

Manawatu u/s 5/03/2013 14:48 10.1 20.5 10.73 8.3 256.7 0.026 0.04 0.022 0.17 0.007 0.007 0 0.68 16

Manawatu u/s 6/03/2013 9:00 10.3 17.9 8.73 7.9 257.6 0.019 0.021 0.015 0.158 0.0031 0.001 0.0021 0.86 4 24.0 9.9 26.2

Manawatu u/s 8/03/2013 14:49 10.1 22.1 10.75 8.4 257.7 0.011 0.011 0.016 0.189 0.013 0.001 0.012 0.62 25

Manawatu u/s 11/03/2013 10:36 9.6 19.7 9.34 8.2 257.5 0.014 0.015 0.018 0.176 0.001 0.001 0 0.85 4

Manawatu u/s 13/03/2013 10:40 9.3 18.6 9.64 8.12 260.6 0.014 0.011 0.016 0.141 0.0067 0.002 0.0047 1 12

Manawatu u/s 14/03/2013 9:00 9.3 18.3 8.1 246 0.013 0.013 0.016 0.136 0.01 0.0001 0.01 0.84 21 25.1 9.5 19.9

Manawatu u/s 20/03/2013 7:35 72.2 15.3 8.78 7.7 155.7 0.021 0.021 0.088 0.808 0.3539 0.018 0.3359 35.4 393

Manawatu u/s 27/03/2013 8:36 12.5 17.4 8.64 7.5 223.3 0.017 0.012 0.02 0.276 0.0256 0.0001 0.0256 1.31 127 70.2 0.0 10.9

Manawatu u/s 3/04/2013 9:06 7.9 258.8 0.012 0.013 0.014 0.193 0.0005 0.0001 0.0005 0.768 48 70.2 26.4 22.0

Manawatu u/s 10/04/2013 15:21 8.5 204.9 0.013 0.005 2.97 129.2 83.3 0.0 18.3

Manawatu u/s 16/04/2013 85.1 0.0 5.6

Manawatu u/s 1/05/2013 5.3 1.5 0.0



Site 1 Date

Flow

(m3/s)

Discharge

eff (m3/s)

Temperature

(oC)

DO

(g/m3)

pH

(lab/field)

Field EC

(uS/cm)

DRP HRC

(g/m3)

TDP

(g/m3)

TP

(g/m3)

TN

(g/m3)

SIN

(g/m3)

NH4-N

(g/m3)

NNN

(g/m3)

Turbidity

EPA

(NTU)

E. coli

(MPN/100mL)

Chl a

(mg/m2)

Phe

(mg/m2)

PeriWCC

(%)

PNCC STP discharage 7/11/2012 11:08 38.3 0.303 0.044 0.092 1.72 38.372 36.1739 36.123 0.0509 395




PNCC STP discharage 5/12/2012 14:40 25.4 0.277 7.2 817 0.063 0.118 1.231 36.623 38.0281 37.991 0.0371 5.8 25


PNCC STP discharage 20/12/2012 8:00 73.2 0.432 745 3.217 3.219 3.52 32.36 35.3271 35.306 0.0211 16.9 384




















PNCC STP discharage 27/03/2013 9:20 12.5 0.274 7.2 830 0.052 0.08 1.693 42.114 39.2846 39.264 0.0206 6.24 16.4


PNCC STP discharage 10/04/2013 14:11 0.744 7.1 654 0.021 27.95 3.66 1312.8



Appendix 2: Periphyton growth on artificial substrate upstream (u/s)

and downstream (d/s) of WWTP

Trial Site (u/s d/s) Day Chl a

(mg/m2)

Pheo

(mg/m2)

%

Phe:Chla

Dry

Mass

(g/m2)

AFDM

(g/m2)

Ash

Mass

(g/m2)

AFDM:Chl a

(AI)

% organic

(AFDM:dryM)

velocity

(cm/s)

A u/s 7 11.52 0.13 1% 41.0 4.5 36.5 390.7 11.0%

A u/s 11 16.05 1.28 8% 44.8 4.9 39.9 306.3 11.0%

A u/s 14 9.31 0.54 6% 77.1 7.1 70.0 759.3 9.2%

A u/s 18 4.77 1.01 21% 159.8 6.8 153.1 1415.2 4.2%

A u/s 21 3.41 0.00 0% 49.2

A u/s 21 3.12 0.00 0% 58.4

A u/s 21 4.02 0.00 0% 49.2

A u/s 21 2.74 0.00 0% 54.2

A u/s 21 2.46 0.00 0% 49.2

A d/s 7 68.54 0.00 0% 110.2 8.9 101.3 129.8 8.1%

A d/s 11 162.22 22.36 14% 114.0 16.2 97.8 100.0 14.2%

A d/s 14 361.24 127.52 35% 192.4 32.4 160.0 89.8 16.9%

A d/s 18 453.10 62.87 14% 255.6 37.0 218.6 81.6 14.5%

A d/s 21 103.86 6.67 6% 49.2

A d/s 21 109.78 7.96 7% 58.4

A d/s 21 440.05 57.51 13% 66.3

A d/s 21 337.10 52.22 15% 73.3

A d/s 21 204.99 19.02 9% 79.8

B u/s 7 10.47 0.00 0% 163.5 5.5 158.0 525.3 3.4%

B u/s 11 2.93 0.49 17% 163.6 5.6 158.0 1910.2 3.4%

B u/s 14 3.02 0.33 11% 187.4 4.3 183.2 1405.1 2.3%

B u/s 18 6.28 0.25 4% 138.8 3.9 134.9 620.8 2.8%

B d/s 7 133.32 0.00 0% 96.0 10.9 85.1 81.8 11.4%

B d/s 11 242.35 14.23 6% 192.3 21.1 171.2 87.1 11.0%

B d/s 14 315.80 21.45 7% 280.2 30.6 249.7 96.8 10.9%

B d/s 18 188.44 1.77 1% 266.8 19.0 247.8 100.9 7.1%

D u/s 7 40.41 2.55 6% 45.6 8.9 36.8 219.0 19.4%

D u/s 11 13.12 1.35 10% 45.7 7.4 38.3 563.9 16.2%

D u/s 15 26.52 2.62 10% 159.3 17.0 142.3 640.9 10.7%

D u/s 18 197.53 14.21 7% 367.3 30.3 337.0 153.6 8.3%

D u/s 21 15.03 2.35 16% 126.3 20.6 105.7 1367.5 16.3% 54.2

D u/s 21 33.71 2.37 7% 143.9 22.2 121.7 658.3 15.4% 62.6

D u/s 21 41.45 5.12 12% 206.9 42.4 164.5 1023.3 20.5% 62.6

D u/s 21 16.85 0.86 5% 67.5 15.7 51.9 929.3 23.2% 57.1

D u/s 21 53.30 6.72 13% 137.7 27.4 110.3 514.3 19.9% 54.2

D u/s 25 31.43 3.33 11% 102.5 17.0 85.5 539.8 16.6% 49.2

D u/s 25 37.81 1.88 5% 141.0 27.4 113.6 725.0 19.4% 53.4

D u/s 25 32.34 1.77 5% 107.0 22.5 84.5 696.2 21.0% 54.2

D u/s 25 33.71 4.99 15% 81.6 18.6 63.0 551.8 22.8% 54.2

D u/s 25 29.15 3.97 14% 135.7 21.9 113.9 749.9 16.1% 58.4

D d/s 7 302.93 15.09 5% 210.6 22.2 188.4 73.3 10.5%

D d/s 11 177.29 11.47 6% 380.0 33.0 347.0 186.1 8.7%

D d/s 15 31.64 2.36 7% 187.0 23.5 163.5 742.7 12.6%

D d/s 18 221.13 32.97 15% 494.2 39.6 454.6 179.1 8.0%

D d/s 21 217.29 4.43 2% 180.5 28.1 152.4 129.2 15.6% 34.2

D d/s 21 397.69 34.60 9% 342.3 61.3 281.0 154.3 17.9% 62.6

D d/s 21 307.94 93.19 30% 281.3 38.8 242.5 126.1 13.8% 73.3

D d/s 21 348.94 90.23 26% 396.5 57.8 338.7 165.5 14.6% 73.3

D d/s 21 315.23 47.52 15% 436.6 58.7 377.9 186.3 13.5% 76.4

D d/s 25 242.35 7.25 3% 280.3 34.3 246.0 141.4 12.2% 49.2

D d/s 25 323.43 24.89 8% 289.1 40.5 248.7 125.1 14.0% 54.2

D d/s 25 599.95 41.60 7% 467.3 79.9 387.3 133.3 17.1% 73.3

D d/s 25 573.98 43.95 8% 383.4 67.9 315.5 118.3 17.7% 57.1

D d/s 25 390.85 68.99 18% 365.1 59.4 305.8 151.9 16.3% 76.4



Trial Site (u/s d/s) Day Chl a

(mg/m2)

Pheo

(mg/m2)

%

Phe:Chla

Dry

Mass

(g/m2)

AFDM

(g/m2)

Ash

Mass

(g/m2)

AFDM:Chl a

(AI)

% organic

(AFDM:dryM)

velocity

(cm/s)

D d/s 1200m 21 496.54 56.78 11% 247.0 51.6 195.5 103.8 20.9% 19.8

D d/s 1200m 21 403.61 72.30 18% 234.6 48.6 186.0 120.5 20.7% 31.3

D d/s 1200m 21 384.48 52.73 14% 325.3 61.3 264.0 159.6 18.9% 54.2

D d/s 1200m 21 248.27 44.95 18% 267.3 50.6 216.7 203.7 18.9% 54.2

D d/s 1200m 21 324.80 37.63 12% 323.7 53.8 269.9 165.8 16.6% 62.6

D u/s longburn 21 153.52 20.97 14% 86.8 28.4 58.4 184.9 32.7% 31.3

D u/s longburn 21 122.54 10.95 9% 124.3 19.9 104.4 162.4 16.0% 28.0

D u/s longburn 21 126.64 11.44 9% 167.4 24.5 142.9 193.3 14.6% 24.2

D u/s longburn 21 157.62 14.25 9% 130.9 22.8 108.0 144.9 17.5% 28.0

D u/s longburn 21 139.40 9.84 7% 180.8 25.5 155.3 182.6 14.1% 31.3

D d/s longburn 21 127.10 14.60 11% 168.1 21.5 146.5 169.5 12.8% 19.8

D d/s longburn 21 220.48 20.92 9% 334.1 39.8 294.3 180.6 11.9% 28.0

D d/s longburn 21 204.54 15.54 8% 200.7 27.1 173.6 132.4 13.5% 19.8

D d/s longburn 21 189.50 19.10 10% 170.3 30.0 140.3 158.4 17.6% 28.0

D d/s longburn 21 425.47 57.33 13% 234.3 40.5 193.8 95.1 17.3% 37.0



Appendix 3: Nutrient diffusing substrate results (18 March 2013)

Site1 Site2 Treatment Client ID

Chl a

(mg/m2)

Pheophytin

(mg/m2) Phe/Chl a

downstream d/s A C Site A: Control 95.6 6.9 7.2%





downstream d/s A P Site A - Phosphorus 118.8 11.6 9.7%





downstream d/s A N Site A - Nitrogen 106.0 9.1 8.6%





downstream d/s A N+P+S Site A: N+P+S 187.5 11.0 5.9%





downstream d/s B C Site B - Control 105.4 10.0 9.5%





downstream d/s B P Site B - Phosphorus 71.4 5.2 7.3%





downstream d/s B N Site B - Nitrogen 97.3 14.2 14.6%





downstream d/s B N+P Site B: N+P 126.6 5.8 4.6%







Site1 Site2 Treatment Client ID

Chl a

(mg/m2)

Pheophytin

(mg/m2) Phe/Chl a

upstream u/s C C Site C - Control 71.7 15.6 21.7%





upstream u/s C P Site C - Phosphorus 70.3 18.6 26.4%





upstream u/s C N Site C - Nitrogen 91.2 14.4 15.8%





upstream u/s C N+P+S Site C: N+P+S 160.6 8.8 5.5%





upstream u/s D C Site D - Control 82.8 17.5 21.2%





upstream u/s D P Site D - Phosphorus 50.2 12.1 24.2%





upstream u/s D N Site D - Nitrogen 116.1 9.9 8.5%





upstream u/s D N+P Site D: N+P 135.0 9.2 6.8%







Appendix 4: Sediment trapped within periphyton mat

us ds Site treatment rep pH

sample

area

(cm2)

Al

dissolved

(mg/m2)

Al Total

(mg/m2)

Ca-

Dissolved

(mg/m2)

Ca Total

(mg/m2)

Fe

Dissolved

(mg/m2)

Fe Total

(mg/m2)

NH4-N

(mg/m2)

NNN

(mg/m2)

SIN

(mg/m2)

DRP

(mg/m2)

TP

(mg/m2)

TSS

(mg/m2)

VSS

(mg/m2) %VSS Al:TSS Ca:TSS Fe:TSS TP:TSS

ds d/s original 1 6.58 228.8 2.67 855 124.2 700 1.85 1172 13.05 3.628 16.68 0.122 63.8 70,367 10,052 14.3% 1.22% 0.99% 1.67% 0.091%

ds d/s original 2 6.78 227.6 2.20 1481 180.8 1221 1.01 2239 7.23 1.538 8.77 0.048 58.3 162,566 14,060 8.6% 0.91% 0.75% 1.38% 0.036%

ds d/s original 3 6.78 227.6 2.47 1204 218.8 1138 1.46 1751 13.75 3.779 17.53 0.395 60.7 155,097 13,620 8.8% 0.78% 0.73% 1.13% 0.039%

ds d/s original 4 6.75 225.1 2.08 1211 123.6 565 1.19 1733 8.25 2.976 11.23 1.288 47.4 161,262 13,327 8.3% 0.75% 0.35% 1.07% 0.029%

ds d/s original 5 6.64 192.9 3.30 2523 202.5 982 2.63 3827 17.00 9.746 26.75 3.401 85.6 273,717 22,291 8.1% 0.92% 0.36% 1.40% 0.031%

ds d/s pH 8.5 1 8.58 228.8 3.63 110.9 1.79 0.498

ds d/s pH 8.5 2 8.48 227.6 4.97 197.1 1.10 0.365

ds d/s pH 8.5 3 8.51 227.6 4.45 236.9 1.54 0.800

ds d/s pH 8.5 4 8.53 225.1 3.75 118.9 1.37 1.568

ds d/s pH 8.5 5 8.52 192.9 6.29 194.2 2.86 4.909

ds d/s pH 9.5 1 9.52 228.8 7.23 98.3 1.88 0.468

ds d/s pH 9.5 2 9.48 227.6 8.50 157.1 1.00 0.663

ds d/s pH 9.5 3 9.47 227.6 9.78 182.6 1.69 1.358

ds d/s pH 9.5 4 9.5 225.1 11.50 90.9 1.34 1.990

ds d/s pH 9.5 5 9.46 192.9 22.54 131.9 2.96 7.356

us u/s original 1 7.13 294.6 1.60 1948 146.6 1140 2.98 3659 5.13 0.441 5.57 2.240 40.3 186,354 15,614 8.4% 1.05% 0.61% 1.96% 0.022%

us u/s original 2 7.08 160.2 2.85 1704 158.3 1140 5.80 2909 6.97 0.499 7.47 3.851 55.4 135,456 13,733 10.1% 1.26% 0.84% 2.15% 0.041%

us u/s original 3 6.95 211 1.67 2633 143.1 1349 2.69 4832 3.52 0.379 3.90 1.858 44.0 171,090 16,588 9.7% 1.54% 0.79% 2.82% 0.026%

us u/s original 4 6.97 140.5 1.95 3443 207.4 1764 3.49 6224 5.42 1.210 6.63 1.936 56.1 367,972 32,028 8.7% 0.94% 0.48% 1.69% 0.015%

us u/s original 5 6.94 175.4 2.55 2526 153.9 1420 3.33 4288 5.47 0.456 5.93 2.537 53.4 214,937 17,104 8.0% 1.18% 0.66% 1.99% 0.025%

us u/s pH 8.5 1 8.52 294.6 1.86 130.4 2.90 2.155

us u/s pH 8.5 2 8.51 160.2 2.78 130.7 5.53 2.734

us u/s pH 8.5 3 8.56 211 1.83 125.0 2.91 1.422

us u/s pH 8.5 4 8.47 140.5 3.05 211.8 4.19 2.206

us u/s pH 8.5 5 8.46 175.4 3.24 143.8 3.88 1.585

us u/s pH 9.5 1 9.52 294.6 1.87 97.1 2.93 2.766

us u/s pH 9.5 2 9.51 160.2 3.85 113.0 5.82 4.332

us u/s pH 9.5 3 9.49 211 2.62 121.7 3.19 1.867

us u/s pH 9.5 4 9.49 140.5 3.11 134.2 3.68 3.267

us u/s pH 9.5 5 9.54 175.4 3.24 101.4 3.96 2.828



Appendix 6: Photos from artificial substrates Trial A, B and D.

Effects of Palmerston North City’s Wastewater Treatment Plant discharge on water quality and aquatic life in the Manawatu River

Joint monitoring programme between Palmerston North City Council and Horizons Regional Council

PORTER

Typewritten Text

ANNEX A TO ITEM 8 Report No. 12-155

Effects of Palmerston North City’s Wastewater Treatment Plant discharge on water quality and aquatic life the Manawatu River

Joint monitoring programme between Palmerston North City Council and Horizons Regional Council

Prepared By Opus International Consultants Limited

Keith Hamill Concordia House, Pyne Street Principal Environmental Scientist PO Box 800

Whakatane, New Zealand

Reviewed By Telephone: +64 7 3082573

Facsimile: +64 7 3084757 Peter Askey (Opus)

Date: 9 September 2012 Reference: 2-34129.00 Status: Final v2

This document is the property of Opus International Consultants Limited. Any unauthorised employment or reproduction, in full or part is forbidden.

© Opus International Consultants Limited 2012

Effects of Totara Rd WWTP discharge on the Manawatu River.

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Contents

Acknowledgements ...................................................................................................................... 1

Executive Summary ...................................................................................................................... 2

1 Introduction .......................................................................................................................... 5

1.1 Background .................................................................................................................. 5

1.2 Purpose of joint work programme ................................................................................. 5

1.3 One Plan Water Quality Targets ................................................................................... 6

1.4 Overview of the joint work programme ......................................................................... 7

1.5 Statistical analysis ........................................................................................................ 8

2 Synoptic surveys ................................................................................................................. 9

2.1 Aim ............................................................................................................................... 9

2.2 Method ......................................................................................................................... 9

2.3 Results and discussion ............................................................................................... 13

2.4 Summary of the synoptic surveys ............................................................................... 22

3 Water quality survey .......................................................................................................... 24

3.1 Aim ............................................................................................................................. 24

3.2 Method ....................................................................................................................... 24

3.3 Results ....................................................................................................................... 25

3.4 Summary .................................................................................................................... 33

4 Periphyton dynamics ......................................................................................................... 34

4.1 Aim ............................................................................................................................. 34

4.2 Method ....................................................................................................................... 34


4.4 Summary .................................................................................................................... 48

5 Nutrient limitation .............................................................................................................. 50

5.1 Aim ............................................................................................................................. 50

5.2 Method ....................................................................................................................... 50


5.4 Summary .................................................................................................................... 65

6 Aquatic macroinvertebrates and periphyton cover ......................................................... 68

6.1 Aim ............................................................................................................................. 68

6.2 Method ....................................................................................................................... 68

6.3 Results ....................................................................................................................... 71

7 Synthesis and Conclusions .............................................................................................. 83


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7.1 Effects of the WWTP discharge on periphyton growth and aquatic macroinvertebrate

communities. ....................................................................................................................... 83

7.2 What is causing the effects observed in the Manawatu River downstream of the

WWTP plant ........................................................................................................................ 84

7.3 Potential management actions.................................................................................... 86

References .................................................................................................................................. 88

Appendix 1: Photographs of samples sites .............................................................................. 91

Appendix 2: Result of aquatic macroinvertebrate sampling in Manawatu River, 20th April 2012 and 27th April 2012 ............................................................................................................. 92

Appendix 3: Results of synoptic survey 19th April and 26th April 2012. .................................. 94

Appendix 4: Results of water quality monitoring in the Manawatu River upstream and downstream of the Totara Road wastewater treatment plant (Nov 2011 to May 2012). ....... 95

Appendix 5: Results of nutrient diffusing substrate periphyton bioassay ............................. 96

Appendix 6: Impact of the treatment wetland on the Totara Road WWTP discharge ............ 97


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Acknowledgements

A number of people have contributed to support the investigations and improve this report.

The work was jointly funded by Palmerston North City Council and Horizons Regional

Council and most of the regular field work was carried out by Horizons Regional Coucil

staff. Particular thanks to:

Jon Roygard and Logan Brown (Horizons RC),

Phil Walker and Rob Green (PNCC).

John Quinn (NIWA) and Cathy Kilroy (NIWA) for their very helpful and constructive

review comments.


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Executive Summary

The Palmerston North wastewater treatment plant (WWTP) was upgraded in 2008 to

reduce phosphorus (P) in the discharge during periods of low flow in the Manawatu River.

The aim of the upgrade was to reduce periphyton biomass and the impact on the aquatic

macroinvertebrate community. It was predicted that this would result in a partial

improvement but that periphyton biomass would still exceed guideline values after about 18

days of accrual.

Concern was raised about the effect of the WWTP discharge on aquatic life after sampling

in early 2011 found more periphyton and a decline in the quality of the macroinvertebrate

community (as measured by QMCI) downstream of the discharge. This resulted in

Palmerston North City Council and Horizons Regional Council undertaking a joint

programme to investigate the impacts of the Totara Road WWTP discharge on water

quality, periphyton and macroinvertebrates in the Manawatu River.

Monitoring and investigations were undertaken in the Manawatu River from November 2011 to May 2012. It included weekly monitoring of water quality and periphyton cover, a synoptic survey to identify if the WWTP discharge was the main source of nutrients to the river, aquatic macroinvertebrate sampling and experiments to determine nutrient limitation. It was a wet summer so some of the investigations were delayed until a period of low flow in April 2012.

The purposes of the joint work programme were to identify:

The extent and magnitude of effects occurring in the periphyton and aquatic

macroinvertebrate communities downstream of the WWTP.

The causes of these effects.

What future management actions may be required for the treatment processes to

reduce adverse effects on the river environment.

The magnitude and extent of effects on aquatic life

Periphyton grew substantially faster at sites downstream of the WWTP discharge, so that

during periods of low flow periphyton biomass exceeded the targets in the Proposed One

Plan (POP) after 17 and 19 days of accrual (for sites 800m downstream and 1400m

downstream respectively) compared to 37 days of accrual required upstream of the

discharge.

The quality of the aquatic macroinvertebrate community (as measured by QMCI) declined

as periphyton biomass increased, and during a period of low flow was significantly lower

downstream of the discharge. The second week of macroinvertebrate sampling (after 29

days of periphyton accrual and 15 days of less than half median river flows) found a

substantial decline in the abundance of mayfly and other EPT taxa at the downstream

sites, which represented a significant adverse effect on aquatic life. This degree of impact

was predicted to occur, on average, 1.2 times per summer at sites about 800m

downstream of the discharge.


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The cause of these effects

The investigations found that the effects on periphyton and macroinvertebrates were not

simply due to phosphorus in the discharge during periods of low flow. When the discharge

was being treated for P, there was more bioavailable P measured in the river than could be

explained by the discharge. At the site 800m downstream a 160% increase in DRP was

measured compared to upstream, but only 7% to 23% could be explained by the effluent

discharge occurring at the time. The unexplained loads estimated during the synoptic

surveys were 7 to 11 kg/day.

Furthermore, while the site 1400m downstream had similar periphyton growth than what

was predicted based on measured dissolved reactive phosphorus (DRP) concentrations,

the site upstream had substantially less periphyton than predicted, and the site 800m

downstream had substantially more.

Two mechanisms might explain the additional DRP measured in the river. Firstly, the

synoptic survey found evidence of groundwater seepage entering the river. This might be

contributing to the load of DRP although it is doubtful that this could explain the magnitude

of load observed. Secondly, river sediments might be desorbing P to the overlying water

during periods of low flow when the WWTP is treating for P.

Two mechanisms might explain the faster than predicted periphyton growth at the site

800m downstream. Firstly, periphyton might be experiencing higher DRP concentrations at

the sediment surface than that measured in the water as P enters from groundwater

seepage and/or desorption from sediments. Secondly, heterotrophic biofilms, stimulated by

carbon in the discharge, might be conditioning the substrate and stimulating periphyton

growth.

The weight of evidence from bioassay experiments indicated that periphyton biomass at

the upstream site was primarily limited by something other than nitrate or phosphorus, but

phosphorus provided secondary limitation. We speculated that the primary limiting factor(s)

at the upstream site might be micronutrients (e.g. cobalt, molybdenum, silica), and/or

grazing by macroinvertebrates. Limitation by ammoniacal nitrogen could not be ruled out.

Future management actions to reduce the effects on aquatic life

Potential management actions to reduce the effect of the discharge on aquatic life include:

Keep treating the discharge for P during periods of low river flow because it is

helping limit the extent of periphyton growth.

Once started continue treating the discharge for P until periphyton cover is reduced

to avoid pulses of P while there is still periphyton cover.

If river sediment is found to be desorbing DRP then start treating for P before the

current trigger of half median flow so there is less sediment derived P by the time

the river reaches low flow.


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Some further investigations would help direct and refine the most appropriate management

actions to reduce the effect of the discharge on aquatic life. The key questions to address

are:

To what extent (if any) are river sediments desorbing P during periods of low flow

when the discharge is removing P? This has implications for the period of time that

P should be removed from the discharge.

Do heterotrophic biofilms stimulate periphyton growth and P availability at the site

800m downstream? This may have implications for the treatment of BOD in the

discharge.

Are low concentrations of micronutrients (e.g. Si, Co, Mo) or ammoniacal nitrogen

limiting periphyton growth upstream? If so, there may be implications of specific

treatment processes.

How much dissolved P does groundwater contribute to this section of the river and

what is elevating dissolved P in the groundwater? If nutrient loads from groundwater

loads are found to be significant than more attention would be justified for reducing

nutrient sources to groundwater, these are most likely to be leakage from ponds at

the WWTP or, to a lesser extent, the landfill.

To what extent are macroinvertebrate grazers controlling periphyton growth? This

has more general implications for understanding periphyton dynamics in the

Manawatu River.


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1 Introduction

1.1 Background

In 2008 the Totara Road Wastewater Treatment Plant (WWTP) was upgraded to remove

phosphorus by alum dosing. This upgrade reduced the phosphorus load entering the

Manawatu River with the discharge and was anticipated to reduce the amount of periphyton

downstream and reduce the consequent impact on the aquatic macroinvertebrate

community.

At the time of granting the consent it was predicted that the upgrade would result in a

partial improvement and that in-stream periphyton guidelines would still be exceeded

downstream of the discharge after 18 to 19 days of accrual1 (respective values from

Cameron 2002, Biggs and Kelly 2002).

In January 2011 a survey was undertaken by Palmerston North City Council (PNCC) of

benthic ecology in the Manawatu River upstream and downstream of the Totara Road

Wastewater Treatment Plant (WWTP) (Cameron 2011). This survey found that despite a

reduction and phosphorus accrual since the 2008 upgrade, periphyton cover at sites

between 800m to 1400m downstream of the WWTP could still reach high levels. During a

period of low flow the site downstream of the WWTP had a statistically significant elevation

of periphyton cover and a corresponding decline in the quality of the aquatic

macroinvertebrate community (as indicated by the SQMCI) compared to upstream sites.

Horizons Regional Council expressed concern about the reported decline in the SQMCI

beyond the 20% target in the Proposed One Plan, and concern that this might have

constituted a breach of Condition 3 f of the discharge permit (number 101829)2 which

states that:

“3. The discharge shall not:

f. cause significant adverse effects on aquatic life”.

After a series of discussions between PNCC and Horizons it was agreed to develop of a

joint programme of work to further investigate the issue. The joint river work programme

was endorsed in a Memorandum of Understanding (MoU) between PNCC and Horizons

RC dated 7th November 2012.

1.2 Purpose of joint work programme

This report describes the result of the joint river work programme. The purposes of the joint

work programme as stated in the MoU were to address:

The effects that are occurring in the periphyton and aquatic macroinvertebrate

communities downstream of the WWTP.

1 Assuming average in-stream DRP concentration of 15 mg/m

3.

2 This was issued under the Manawatu Catchment Water Quality Regional Plan.


2-34129.00

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The causes of these effects (including effects of flows and other sources of

contaminants besides the WWTP).


lessen adverse effects on the river environment.

The technical aims of the monitoring programme were to:

Clarify the extent to which the PNCC WWTP discharge is affecting periphyton growth

and the aquatic macroinvertebrate community in the Manawatu River.

Identify the extent to which other sources of contaminants may influence the

Manawatu River between the upstream and downstream sample points.

Identify which if any nutrient is limiting periphyton growth upstream and downstream of

the discharge – particularly at flows less than 40 m3/s when the P treatment is

occurring.

Provide guidance on modifications to the treatment process to reduce any adverse

effect on the river environment, which may include refining the timing and extent of

wastewater phosphorus removal in order to limit downstream periphyton growth.

1.3 One Plan Water Quality Targets

Schedule D of the Proposed One Plan (POP) sets water quality targets for rivers in the

Manawatu-Whanganui Region. The Manawatu River near the PNCC WWTP discharge is

in zone “Lower Manawatu Mana_11a”, water quality targets particularly relevant to this

zone are:

The algal biomass on the river bed must not exceed 120 mg of chlorophyll a per square metre.

The maximum cover of visible river bed by periphyton as filamentous algae more than 2 centimetres long must not exceed 30%.

The maximum cover of visible river bed by periphyton as diatoms or cyanobacteria more than 0.3 centimetres thick must not exceed 60 %.

The annual average concentration of dissolved reactive phosphorus (DRP) when the river^ flow is at or below the 20th flow exceedance percentile must not exceed 0.001 grams per cubic metre, unless natural levels already exceed this target.

The annual average concentration of soluble inorganic nitrogen (SIN)3 when the river^ flow is at or below the 20th flow exceedance percentile must not exceed 0.444 grams per cubic metre, unless natural levels already exceed this target.

The Macroinvertebrate Community Index (MCI) must exceed 100, unless natural physical conditions are beyond the scope of application of the MCI.


2-34129.00

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There must be no more than a 20 % reduction in Quantitative Macroinvertebrate Community Index (QMCI) score between appropriately matched habitats upstream and downstream of discharges to water.”

1.4 Overview of the joint work programme

The joint work programme consisted of five investigations in the Manawatu River upstream and downstream of the Totara Road WWTP. These were:

A synoptic survey river water quality to identify whether there are other potential

nutrient sources (other than the WWTP) between the upstream and downstream

monitoring sites (undertaken on 19 April and 26 April).

Weekly water quality monitoring of the Totara Road WWTP discharge and in the

Manawatu River at one site upstream and two sites downstream of the discharge. An

analysis of the effects of the treatment wetland on the discharge quality was also

undertaken (see Appendix 6).

Weekly monitoring of periphyton cover and biomass to better understand periphyton

dynamics.

Nutrient limitation bioassay (in the river for 13 days from 14th to 27

th April) and analysis

of cellular nutrient concentrations (25th January, 21

st April and 28

th April) to better

understand which nutrient, if any, is limiting periphyton growth upstream and

downstream of the discharge during a period of low flow when the WWTP is treating

for phosphorus. A bioassay array was also placed in the river for five days from 29th

March to 3rd April but had to be removed due to a flood.

Aquatic macroinvertebrate and periphyton sampling to clarify the extent to which the

Totara Rd WWTP is affecting the aquatic macroinvertebrate community. This involved

sampling four sites (two upstream and two downstream) on two sequential occasions

during a period of low flow when the WWTP was treating for phosphorus (P)

(undertaken on 20th and 27

th April).

The data collection and field surveys of the river were primarily undertaken by Horizons RC

field staff and was integrated with other monitoring of the Manawatu River occurring during

the summer.

Many of the planned investigations required sampling during a period of low flow and when

the WWTP was treating for phosphorus. The summer of 2011/12 was very wet, and an

extended period of low flow conditions did not occur until mid-April. A summary of when the

different monitoring occurred with respect to flow is shown in Figure 1.1.


2-34129.00

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0

50

100

150

200R

ive

r fl

ow

(m

3/s

)

River flow

WQ + algae

cellular nutrients

bioassay

Synoptic survey

invertebrates

Figure 1.1: Timing of surveys and investigations overlaid on flow in the Manawatu River (at

Teachers College). The red line indicates flows of 37 m3/s (half median flow) below which

the WWTP must be treating for phosphorus. The top of the scale (220 m3/s) represents a

flow of three times median flow.

1.5 Statistical analysis

The statistical significance of water quality results, periphyton cover and macroinvertebrate

indices was compared using a non-parametric Mann-Whitney test and an equivalence test

in the software „TimeTrends‟. The data from upstream sites and downstream sites were

pooled, which incorporates both within site diversity and between site diversity. A difference

was considered statistically significant if the p-value was < 0.05.

Equivalence tests incorporate both testing of means (using a student t-test) and testing of a

meaningful change (interval testing). One advantage of equivalence tests is that it is less

sensitive to sample size. Increasing the sampling effort may make it either more or less

likely that an equivalence hypothesis will be rejected, unlike a statistic test comparing mean

values, where more data makes it more likely that the hypothesis will be rejected.


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2 Synoptic surveys

2.1 Aim

There has been speculation that in addition to the PNCC WWTP discharge there might be

some other potential sources of nutrients in the 1.8 km between the upstream and

downstream sampling points. We were asked to consider the possibility of alternative

nutrient sources to the Manawatu River which could include:

Turitea Stream entering on the true left opposite the upstream sample point;

Palmerston North City Council closed landfill on the true right;

Possible leaching via groundwater from the sludge storage ponds;

Kahuterawa Stream on the true left just upstream of the first downstream sampling

site.

2.2 Method

Surveys of a range of water quality variables were conducted in the river reach from 1 km

upstream of the WWTP discharge to 2.5 km downstream of the discharge (150m

downstream of Mangaone Stream confluence). The surveys took place on 19 and 26 April

during a period of low flow when the WWTP was removing phosphorus, with the aim of

identifying changes in water quality associated with the potential additional nutrient

sources.

Electrical conductivity, temperature and dissolved oxygen measurements were made in the

field at approximately 100m intervals between the discharge point and the 800m

downstream site in the main stem of the Manawatu River. Water quality samples were

collected at nine sites on the Manawatu River, as well as from the discharge, from the

Turitea Stream (entering about 1100m upstream on the true left), the Kahuterawa Stream

(entering about 820m downstream on the true left) and the Mangaone Stream (entering

about 2250m downstream on the true right). All Manawatu River samples from 800m

downstream upwards were collected from the true right bank, while from 1400m

downstream they were collected on the true left due to access. The sample locations are

shown in Figure 2.1. Photo 1 shows the Manawatu River at 400m downstream at this point

there is evidence of fly tipping or possibly old landfill material (e.g. plastic wrap and

concrete) amongst the eroded gravel bank of the river (see Photo 2).

Water quality samples were stored in a cool chilli-bin and sent to Watercare Laboratories

overnight to test for the following variables: electrical conductivity (EC), pH, cBOD5, total

nitrogen (TN), nitrate-nitrogen, nitrite-N, total ammoniacal-N (NH4-N), total phosphorus

(TP), total dissolved phosphorus (TDP), dissolved reactive phosphorus (DRP), E. coli bacteria, total hardness, a suite of organic compounds, and a suite of trace elements and

metals (dissolved and total fractions) including: aluminium (Al), calcium (Ca), chromium

(Cr), copper (Cu), iron (Fe), lead (Pb), magnesium (Mg), manganese (Mn), nickel (Ni),

potassium (K), sodium (Na), zinc (Zn), arsenic, boron (B), chloride (Cl) and sulphur (S).

Soluble inorganic nitrogen (SIN) was calculated from nitrate, nitrite and total ammonia.


2-34129.00

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Variables that are typically elevated as a result of any landfill influence include: iron, boron,

chloride, potassium, zinc and total ammonia.

Figure 2.1: Water quality sample sites for the synoptic survey on 19th and 27

th April. White

circles indicate the discharge and tributaries. Additional electrical conductivity

measurements were taken every 100m between the discharge point and the 800m

downstream monitoring site.


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Photo 1: Manawatu River at 400m downstream of the discharge, facing upstream during

about median flow.

Photo 2: Evidence of fly tipping or possibly old landfill material exposed by the river at

about 400m downstream of the discharge.


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2.2.1 Adjusting for dilution

Salinity or electrical conductivity (EC) is often used as a conservative tracer in mixing

studies. Because the WWTP discharge has considerably higher EC compared to the

Manawatu River upstream (i.e. about 808 µS/cm compared to 216 µS/cm), the EC in the

discharge itself can be used to estimate dilution at sampling points downstream.

Dilution was calculated using a mass balance approach over a „control volume‟ of the river

after mixing. The formula for the dilution factor (D) for downstream sampling points is:

D = (ECeff – ECu/s)/(ECd/s – ECu/s)

Where: D = dilution factor; ECeff = electrical conductivity of the effluent; ECu/s = EC of the

river upstream; ECd/s = EC of the river downstream.

The dilution factor obtained from this method for each sample location was then used to

calculate a theoretical concentration (assuming no in-river attenuation) for variables of

interest using the following formula:

Cd/s = ((Ceff – Cu/s) / D) + Cu/s)

Where: D = dilution factor, Ceff = concentration in the effluent; Cu/s = concentration in the

river upstream; Cd/s = concentration in the river downstream.

An estimate was also made of the theoretical dilution available if the effluent was fully

mixed with the river. This was done using measurements of electrical conductivity and

discharge volume from the effluent and the Manawatu River upstream. The following

formula was used:

EC fully mixed = ((upstream EC x river flow) + (discharge EC x discharge flow)) / (river

flow + discharge flow)

These methods assume a relatively constant EC in the discharge and in the river over the

period of sampling. EC in rivers can vary diurnally as a result of photosynthesis and

respiration. Photosynthesis uses carbon dioxide from the water which shifts the balance of

bicarbonate ions in the water, increasing pH and, to a much lesser extent, increasing the

EC during the day. Samples were collected over a four hour period from downstream to

upstream so any diurnal change would result in a slight under-estimate of dilution, however

fifteen minute measurements of EC in the Manawatu River at the Teaches College shows

that there was very little change in electrical conductivity during the day.


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2.3.1 General results

The results of water quality sampling on 19th April and 26

th April are shown in Appendix 3.

The discharge had elevated concentrations of a number of variables including: cBOD5,

NH4-N, nitrate-nitrite-N, TN, DRP, E.coli bacteria, zinc, aluminium and dissolved iron. For a

number of variables the discharge had lower concentrations than the tributaries.

Concentrations of all organic compounds were below detection and the results are not

shown in the table.

The Soluble Inorganic Nitrogen (SIN)3 concentration in the Manawatu River upstream of

the discharge was 0.232 g/m3 and 0.051 g/m

3 on 19

th and 26

th April respectively. These

values had respectively increased to 0.88 g/m3 and 0.586 g/m

3 at 800m downstream of the

discharge. The increased nitrogen was primarily due to total ammoniacal nitrogen from the

discharge.

The DRP concentration in the Manawatu River upstream of the discharge was 0.007 g/m3

and <0.005 g/m3 on 19

th and 26

th April respectively

4. These values had respectively

increased to 0.018 g/m3 and 0.011 g/m

3 at 800m downstream of the discharge. As will be

discussed, not all of the increase in DRP can be explained simply by the discharge itself.

2.3.2 Electrical conductivity and dilution

The electrical conductivity5 in the Manawatu River downstream of the WWTP is shown in

Figure 2.1. The calculated dilution factors with distance downstream are shown in Table

2.1. The dilution factors assume dilution due to mixing of the effluent with the river water

and do not account for the influence of tributaries or any groundwater influence. By a

distance of 800m downstream dilution factors based on EC were 60% to 90% of estimates

of full mixing based on mass loads. This is consistent with a mixing study by Rutherford et al. (1997) who found that the effluent was not fully mixed across the river until after the

bend (probably in the vicinity of 1200-1400m downstream of the discharge). At a location

850m downstream of the discharge on the true right bank the total ammonia concentrations

were found to be 1.5 times fully mixed.

EC appeared to be influenced by factors other than dilution of the discharge. Figure 2.2

shows a change in EC on a more detailed scale. As would be expected, EC declined after

the Kahuterawa Stream confluence (entering about 820m downstream) and slightly rised

after the Mangaone Stream confluence (about 2250m downstream). However there was

also a slight increase in EC between sites 600m downstream (Awapuni Shingle Plant) and

800m downstream – suggesting a possible groundwater influence at this point raising the

EC by 1 to 3 µS/cm on the 19th and 26

th April respectively. Small EC changes of this

magnitude are sufficient to explain the lower dilution factor calculated from EC compared to

the estimated dilution factor at full mixing based on mass loads.

3 SIN is nitrate-nitrite nitrogen + total ammoniacal nitrogen and generally considered the forms most available

for periphyton and plant growth. 4 Calculations based on the „less than‟ value on 27 April will have wide error margins.

5 Using EC measured with a meter in the field.


2-34129.00

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80

130

180

230

280

330

380

-1500 -500 500 1500 2500

Elec

tric

al c

ondu

ctiv

ity (u

S/cm

)

Distance from WWTP (m)

Manawatu 19 April

Manawatu 26 April

Tributaries 19 April


discharge

Figure 2.1: Change in electrical conductivity with distance upstream and downstream from

the WWTP discharge (sampling from true right bank).

210

215

220

225

230

235

240

245

250

-1500 -500 500 1500 2500

Elec

tric

al c

ondu

ctiv

ity (u

S/cm

)


Manawatu 19 April

Manawatu 26 April

discharge

Mangaone Stm

Kahuterawa Stm

Groundwater influence?

Figure 2.2: Fine scale change in electrical conductivity with distance upstream and

downstream from the WWTP discharge (sampling from true right bank).


2-34129.00

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Table 2.1: Dilution factor on true right bank of Manawatu River with distance downstream

from WWTP discharge (calculated from electrical conductivity).

Distance d/s (m) Dilution factor 19th April

Dilution factor 26th April

Comment

100 17.1 16.9

200 34.4 27.4

300 43.5 35.0

400 54.7 46.4

500 70.1 61.8

600 66.9 63.7

700 65.5 63.7

800 67.7 73.0

Full mixing 114.6 6 80.3 7 Calculated from daily load

820 Kahuterawa Stream influence

1400 186.2 272.3

1800 198.6 260.4

2250 Mangone Stream influence

2400 229.1 206.6

2.3.3 Change in nutrient concentration

Changes in the concentration of total nitrogen (TN) and soluble inorganic nitrogen (SIN)

along the study reach are shown in Figure 2.3 and Figure 2.4 respectively. The graph

compares measured concentrations with hypothetical concentrations that would occur

solely due to dilution. The observed change in total nitrogen was strongly related to dilution

due to mixing of the WWTP effluent. SIN concentrations were also strongly related to

dilution due to mixing of the effluent, although on 19th April there was about 18%

8 more

SIN measured than expected due to dilution at sites 400m to 800m downstream of the

discharge; this suggests that a small amount of TN may be converting into SIN in this

reach of the river. TN and SIN showed a similar pattern by the time the river was full mixed

at 1400m downstream.

Upstream of the discharge about two thirds of the total nitrogen concentration was in the

form of nitrate, one third in the form of organic nitrogen and only about 4% in the form of

total ammonia (NH4-N). The discharge contributes a considerable load of nitrogen to the

river – predominantly (88% to 90%) in the form of NH4-N and organic N (10% to 12%).

Thus 800m downstream of the discharge total nitrogen was predominantly in the form of

NH4-N (72% to 75%), with a smaller proportion of nitrate (11% to 27%) and organic

nitrogen (1% to 14%). On 19th April there was evidence of about 0.1 mg/l of organic

nitrogen being converted to NH4-N between the sites upstream and 800m downstream of

the discharge.

The change in concentration of total phosphorus (TP) and dissolved reactive phosphorus

(DRP) is shown in Figure 2.5 and Figure 2.6 respectively. As with TN, the results for TP

6 Based on effluent discharge of 0.2361 m

3/s, effluent EC 808 µS/cm, river discharge of 26.822 m

3/s, river EC

212.3 µS/cm. 7 Based on effluent discharge of 0.2755 m

3/s, effluent EC 817 µS/cm, river discharge of 21.844 m

3/s, river EC

218 µS/cm. 8 18% more SIN at site 800m downstream, 0.88 g/m

3 measured compared to 0.747 g/m

3 predicted.


2-34129.00

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show that the observed change in TP was strongly related to dilution due to mixing of the

WWTP effluent. However DRP measured at the site 800m downstream on 19 April was

160% above background concentrations and about 2.4 higher9 than concentrations

expected by simple dilution of the effluent (as estimated by EC). The discharge was

predicted to cause a 7% increase in DRP concentrations10

, with the additional measured

increase probably due to other sources.

Effluent sampling (post-wetland) by PNCC had higher values than effluent samples

collected during the synoptic survey (i.e. 0.114 mg/l compared to 0.04 mg/l on 19th April,

and 0.13 mg/l compared to 0.019 mg/l on 26th April). The change in DRP due to dilution

was calculated using both values and graphed in Figure 2.6. Even based on these higher

values measured concentrations was 2.1 times higher than expected due to dilution. On 19

April the discharge was predicted to cause a 23% increase in DRP concentrations10

, with

the additional measured increase probably due to other sources.

Some studies have total dissolved phosphorus (TDP) to be a better indicator of bioavailable

phosphorus because it included dissolved organic forms that can also be bioavailable (e.g.

Turner et al. 2003). In this survey TDP followed a similar pattern to DRP (see Figure 2.7).

Results from weekly monitor (see next section) found TDP to be, on average, 36% and

14% higher than DRP at sites 800m downstream and 1400m downstream respectively

when flows were less than 40 m3/s.

11 At the site 800m downstream, for 19 and 26 April

respectively, the measured TDP was 0.019 g/m3 and 0.015 g/m

3 i.e. 171% and 150%

higher than upstream. In contrast the predicted TDP for this site was 0.0083 g/m3 and

0.007 g/m3, i.e. 19% and 17% increase from upstream.

One feature of Figure 2.6 and 2.7 is that DRP and TDP concentrations predicted from

dilution calculations appear to be relatively constant with distance downstream compared to

the other variables graphed. This is because the discharge had a relatively low DRP

concentration compared to the river (about 5.7 times the background river concentration),

whereas other variables were proportionally much higher in the discharge e.g. total

phosphorus in the discharge was about 109 times above background river concentrations.

2.3.4 Change in phosphorus load

Another way to examine the potential effects of the WWTP discharge is to compare the

nutrient load from the river and the discharge. Table 2.2 compares the load to DRP and TP

in the Manawatu River upstream and downstream (after full mixing) and from the discharge

and Managone Stream. The results are consistent with the dilution analysis – i.e. there was

an unexplained source of DRP (about 6.9 to 11 kg/day) but a relatively consistent TP.

9 At site 800m downstream on 19

th April measured DRP was 0.018 g/m

3 compared to a predicted value of

0.0075 g/m3. Values from 26

th April were unreliable for this comparison because upstream values were

<0.005 g/m3

10 On 19

th April, upstream DRP was 0.007 g/m

3, 800m downstream was 0.018 g/m

3 and predicted was

0.0075 g/m3 using synoptic survey data and 0.0086 g/m

3 using PNCC effluent data. On 26 April upstream

DRP was <0.005 g/m3, making comparisons uncertain.

11 Mean TDP was 0.0116 and 0.0098 g/m

3 at site 1400m downstream, mean DRP was 0.00855 and 0.00856

g/m3 at site 1400m downstream. Mean concentrations of TDP and DRP in the discharge were 0.0879 and

0.033 g/m3 respectively


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Table 2.2: Load of TP and DRP in the Manawatu River on 19th April 2012 and during low

flows between 11 April – 25th May (n=6).

19th April 11th April – 25th May Site DRP load

(kg/day)

TP load

(kg/day)

DRP load

(kg/day)

TP load

(kg/day)

Manawatu Rv u/s 16.22 25.49 21.23 44.8

Discharge 0.82 24.48 0.577 17.11 Manawatu Rv 1400m d/s - - 28.69 60.68

Manawatu Rv 1800m d/s 28.10 44.5 - -

Mangaone Stm 0.067 0.34 - - Manawatu Rv 2400m d/s 25.79 37.52 - -

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-1500 -500 500 1500 2500

Tota

l Nitr

ogen

(g/m

3 )


Manawatu 19th April

Manawatu 26th April

TN change due todilution 19th April

TN change due todilution 26th April

Tributaries 19th April


discharge

Figure 2.3: Change in total nitrogen with distance upstream and downstream from the

WWTP discharge (sampling from true right bank).


2-34129.00

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0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-1500 -500 500 1500 2500

Solu

ble

Inor

gani

c N

itrog

en (g

/m3 )


Manawatu 19th April

Manawatu 26th April

SIN change due todilution 19th April

SIN change due todilution 26th April



discharge

Figure 2.4: Change in soluble inorganic nitrogen with distance upstream and downstream

from the WWTP discharge (sampling from true right bank).

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

-1500 -500 500 1500 2500

Tota

l Pho

spho

rus

(g/m

3 )


Manawatu 19th April

Manawatu 26th April

TP change due todilution 19th April

TP change due todilution 26th April



discharge

Figure 2.5: Change in total phosphorus with distance upstream and downstream from the

WWTP discharge (sampling from true right bank).


2-34129.00

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0

0.01

0.02

0.03

0.04

0.05

-1500 -500 500 1500 2500

Dis

solv

ed R

eact

ive

Phos

phor

us (g

/m3 )


Manawatu 19th April

Manawatu 26th April

DRP change due todilution 19th AprilDRP change due todilution 26th AprilTributaries 19 April


discharge

Figure 2.6: Change in dissolved reactive phosphorus with distance upstream and

downstream from the WWTP discharge (sampling from true right bank). The dashed lines

show expected change in DRP due to dilution; two estimates are graphed for each date

based on: effluent sample from synoptic survey (lower line), effluent sample from PNCC

compliance sampling (higher line).

0

0.01

0.02

0.03

0.04

0.05

-1500 -500 500 1500 2500

Tota

l Dis

solv

ed P

hosp

horu

s (g

/m3)


Manawatu 19th April

Manawatu 26th April



TDP change due todilution 19th April

TDP change due todilution 26th April

discharge

Figure 2.7: Change in total dissolved phosphorus (TDP) with distance upstream and

downstream from the WWTP discharge (sampling from true right bank). The dashed lines


2-34129.00

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show expected change in DRP due to dilution; two estimates are graphed for each date

based on: effluent sample from synoptic survey (lower line), effluent sample from PNCC

compliance sampling (higher line).

2.3.5 Potential sources of DRP in addition to the discharge

The doubling in DRP concentration compared to the predicted concentration cannot be

simply explained by desorbing of phosphorus attached to particles to a dissolved form

because both pH and dissolved oxygen were high in the river compared to the effluent –

the opposite conditions than what would be expected for desorbing P. A more plausible

explanation is that two separate processes are occurring, whereby some particulate

phosphorus is settling in the river prior to full mixing while at the same time there is another

source of DRP influencing the river downstream of the WWTP discharge.

Potential sources of DRP to the river downstream of the discharge could be:

a) Seepage of groundwater rich in P.

b) Desorption of dissolved phosphorus from the river sediments as the sediments come to

equilibrium with lower P concentrations in the overlying water; or

c) Late mixing of the Turitea Stream (but we this ),

Seepage of groundwater carrying nutrients derived from the ponds near the WWTP or the

landfill could be a source of DRP. If this is occurring then the predicted nutrient

concentrations (based on EC) would be under-estimates and thus the change in DRP

concentration compared to what would be expected from the WWTP discharge would be

more than 2.4 times.

It is possible that when the discharge is not treating for P the sediment acts as a P sink (i.e.

increasing the equilibrium P concentration). When the WWTP is alum dosing for P the

discharge and river concentrations are lower, and some of the P stored in the sediments

could be released back into the water column (see Lucci et al 2010, Haggard and Stoner

2009).

The Turitea Stream had DRP concentrations slightly higher than the treated effluent. The

Turitea Stream confluence with the Manawatu River is on the true left about 1100m

upstream of the discharge, but during the study period the flow of the Manawatu River was

concentrated on the true left so it was considered possible that the Turitea Stream did not

fully mix across the river until some point after the site 600m upstream. However during the

period the Turitea Stream had low flows (about 0.06 m3/s), about a quarter of the volume

from the WWTP and a slight decline (0.1 to 0.4 µS/cm) in EC was observed between the

sites 1200m upstream and 600m upstream, that that was consistent with full mixing of the

Turitea Stream with the Manawatu River. Furthermore, previous monitoring of the Turitea

Stream has shown much lower DRP concentration which counts against this being a long

term contributor of nutrients.


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2.3.6 Potential influence of groundwater on the Manawatu River

The results of the synoptic surveys provides some evidence that groundwater may be

entering the Manawatu River between 600m and 800m downstream of the discharge. This

was evidenced by an increase in the concentration of electrical conductivity (see Figure

2.2), and nitrate-nitrite-nitrogen compared to sites upstream of the discharge and

immediately downstream of the discharge. The concentrations of some other variables do

not decline as quickly as would be predicted by simply dilution of this discharge, these

include: DRP, SIN, and potassium.

Variables are typically elevated as a result of landfill leachate include: total ammonia, iron,

boron, potassium, sodium, manganese and chloride. Groundwater monitoring in the vicinity

of the WWTP and the landfill has shown concentrations of a number of these variables

elevated compared to the river including EC (320 to 1080 µS/cm), total ammonia (0.05 to

76 g/m3), nitrate-nitrite-N (0.1 to 32.8 g/m

3), DRP (up to 0.76 g/m

3). Groundwater DRP

concentrations were highest downstream of the WWTP ponds (and upstream of the

landfill). River measurements were taken near the true right bank of the river and will be

detecting these concentration increases before full mixing of any groundwater with the

river.

It is plausible that nutrients derived from the WWTP ponds or landfill is moving with

groundwater to the river. To confirm the degree of influence and the sources of

contamination would require some further work including collecting groundwater samples

from shallow groundwater adjacent to the river.

Horizons RC surveyed groundwater levels in bores around the landfill and WWTP site in

15th June 2012 when the river flow was about 49 m

3/s. This showed groundwater gradients

shifting towards the southwest as the river flows around the bend. It is likely that

groundwater gradients under the Awapuni shingle plant, landfill and WWTP shift westwards

(towards Mangaone Stream confluence) at higher river levels.

Note that during periods of low flow the Mangaone Stream has very little flow, i.e. about 37

l/s at half median flow which is about 15% of the volume of effluent discharged by the

WWTP. Thus the potential influence of the Managaone Stream on water quality in the

Manawatu River is small.

Groundwater investigations under the Awapuni landfill in 1993 (Earthtec Consulting 1995)

estimated the groundwater flow of the unconfined aquifer to be 1670 m3/day and upward

groundwater leakage in the base of the unconfined aquifer to be 20 m3/day. Assuming a

DRP concentration of 0.4 g/m3 (average of bore MW4) this translates to a DRP load of

0.716 kg P/day. This is about the same DRP load to the river as the discharge during low

flows in April when treating for P (0.6 kg/day) (see Table 2.2), but does not fully explain the

additional 7 kg/day measured downstream. If these estimates are correct then groundwater

seepage would be only a partial explanation for the additional dissolved P concentrations.


2-34129.00

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2.4 Summary of the synoptic surveys

Electrical conductivity was used a tracer to calculate dilution factors as the treated

effluent from the WWTP progressively mixed with the Manawatu River.

Changes in EC values indicated that a groundwater source may have been entering

the river on the true right bank above sites 600m to 800m downstream of the

discharge.

Soluble inorganic nitrogen (SIN) was about 18% higher than what would be

predicted simply by dilution of the effluent. This may be due to organic nitrogen

changing to a dissolved inorganic form, but a contribution of nitrate from a

groundwater influence may also be a contributing factor.

At a distance of 800m downstream, the discharge increased the SIN concentration

in the river from 0.232 g/m3 to 0.88 g/m

3 on 19

th April, and 0.051 g/m

3 to 0.586 g/m

3

on 26th April. The increased SIN was primarily in the form of total ammoniacal

nitrogen and exceeded guideline concentrations for control of periphyton growth.

At a distance of 800m downstream, the discharge and other sources substantially

increased the DRP concentration in the river from 0.007 g/m3 to 0.018 g/m

3 on 19

th

April (a 157% increase), and <0.005 g/m3 to 0.011 g/m

3 on 26

th April. The direct

discharge was predicted to cause a 7% to 23% increase in DRP concentrations (i.e.

0.0005 to 0.0016 g/m3) with the rest due to other sources.

At a distance of 800m downstream, total dissolved phosphorus was measured to be

150% to 170% higher than upstream, while the WWTP was predicted to cause an

increase of only 17% to 19% above upstream concentrations.

Changes in TP concentration was consistent with dilution based on EC. However

DRP measured 800m downstream was 2.4 times higher than concentrations

predicted simply by dilution of the effluent.

Total phosphorus (TP) concentrations were similar to (based on dilution

calculations) or less than (based on load calculations) what was expected due to

the WWTP discharge. This suggests that some particulate P from the alum treated

effluent was precipitating in the river downstream of the discharge.

The disproportionate increase in DRP compared to EC observed during the April

low flow may be explained by:

o Dissolved P carried with groundwater seepage to the river (although load

estimates suggest this might be only a partial explination),

o Desorption of dissolved phosphorus from the river sediments as the

sediments come to equilibrium with lower P concentrations in the overlying

water.


2-34129.00

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The difference between measured and predicted DRP was less on 26th

April

compared to 19th April. This would be consistent with both a reduction in

groundwater head (and thus discharge volume) in the weeks following rain, or DRP

sorbed to sediments coming into equilibrium with overlying river water.

Potential sources of contaminants to groundwater have not been confirmed but

could include the closed landfill site or seepage from WWTP storage ponds. The

location where groundwater enters the river is likely to shift westward towards

Mangaone Stream at higher river flows.

To confirm the degree to which groundwater influences the river water quality and

the source of any contaminants would require some further work including collecting

groundwater samples from shallow groundwater adjacent to the river and surveying

water levels during periods of low flow (i.e. less than half median flow).

To confirm potential desorption of dissolved phosphorus from the river sediments

this would require further work to test the sorption capacity of river sediments.


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3 Water quality survey

3.1 Aim

Weekly river water quality sampling was undertaken to provide information to interpret

observed changes in periphyton cover and composition and to allow more accurate

calculation of mass loads during periods of stable river flow. This in turn was used to

assess the influence of other nutrient sources to the Manawatu River during periods of

stable river flow.

The results presented in this section are further discussed in section 4 in the context of

periphyton dynamics.

3.2 Method

Water quality sampling was undertaken weekly from 16th November 2011 to 25

th May 2012

at the same time as assessments of periphyton cover. The sampling was usually done on a

Wednesday or Thursday. The location of these sites are shown in Figure 3.1, the sites

sampled were:

Manawatu River about 1000m above the discharge point;

Manawatu River about 800m below the discharge point,

Manawatu River about 1400m below the discharge point,

PNCC WWTP discharge prior to the wetland and

PNCC WWTP discharge after the wetland.

Water quality samples were stored in a cool chilli-bin and sent to Watercare Laboratories

overnight to test for the following variables: total nitrogen, nitrate-nitrite nitrogen (NNN),

total ammoniacal nitrogen (NH4-N), total phosphorus (TP), dissolved reactive phosphorus

(DRP), dissolved iron, dissolved magnesium and dissolved aluminium. Instream field

measurements were made for the following parameters in the Manawatu River: electrical

conductivity (EC), dissolved oxygen (DO), pH, and temperature.

In addition, DRP was measured daily from the Totara Road WWTP during periods when

the Manawatu River is half median flow (37 m3/s) and when the WWTP was treating for

phosphorus. Daily flow weighted composite samples were collected prior to the effluent

entering the wetland pond and a daily grab samples was collected after the wetland pond.


2-34129.00

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Figure 3.1: Location of water quality monitoring sites on the Manawatu River and the

WWTP discharge. The location of the discharge is indicated with a yellow arrow.

3.3 Results

3.3.1 Totara Road WWTP discharge monitoring

The concentration of DRP leaving the treatment wetland during low flow periods since

November 2012 is shown in Figure 3.1. The mean DRP concentration during this period

when the river was at half median flow was 0.096 g/m3. In contrast, when the WWTP was

not treating for P the mean concentration discharged was 2.62 g/m3 (mean of monthly

samples between April 2009 and April 2012). During the period when the nutrient bioassay

was in the river (15th April to 28

th April 2012) the mean DRP concentration of the discharge

was 0.078 g/m3 and the mean load of DRP was 1.81 kg/day.

The long term mean DRP discharged during phosphorus treatment (April 2009 to May

2012) was 0.109 g/m3 and the corresponding long term DRP load was 2.63 kg/day.


2-34129.00

13/09/2012 26

A comparison of sampling before and after the wetland found that the concentration of

DRP was on average about 24% lower after the wetland than before it, but there is

considerable variability in the data (see Appendix 6).

0.0

0.1

0.2

0.3

0.4

0.5

0

50

100

150

200

250

DR

P p

ost

we

tlan

d (

g/m

3)

Riv

er

flo

w (

m3

/s)

River flow

DRP

Figure 3.1: Dissolved Reactive Phosphorus concentration in the discharge from the

treatment wetland and corresponding river flow.

3.3.2 River and effluent monitoring

The results of water quality monitoring during November 2011 to May 2012 are shown in

Appendix 4. Table 3.1 shows the median of selected variables for the full period and Table

3.2 shows the median when the WWTP was treating for phosphorus i.e. the flow in the

Manawatu River was about half median flow. The results of a Mann-Whitney statistical test

are shown in Table 3.3.

All variables had median values within the targets set in the One Plan and guideline values

(i.e. ANZECC 2000, periphyton guidelines (Biggs 2000) with the exception of: nitrate,

soluble inorganic nitrogen (SIN), dissolved reactive phosphorus (DRP), periphyton biomass

(as measured by chlorophyll a) and periphyton cover (as measured by the Periphyton

Proliferation Index (PPI)).

SIN was within the One Plan target value (i.e. 0.44 g/m3) at the upstream site but only

dropped to within concentrations that the Biggs (2000) model predicts are needed to

control excessive periphyton growth during low flow periods (i.e. 0.1 g/m3 to 0.295 g/m

3 for

accrual periods of 27 to 30 days respectively). There was a statistically significant increase

in SIN between the upstream and both downstream sites, which were primarily due to

additional ammonium from the discharge (see Figures 3.2 and 3.3).


2-34129.00

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For the full data set, median DRP in the river upstream and downstream of the discharge

exceeded the One Plan target value12

(i.e. 0.01 g/m3) but were within periphyton guideline

values to avoid excessive periphyton growth assuming a 20 day accrual period (i.e. <0.026

g/m3) (Biggs 2000). The DRP concentrations were significantly higher at the site 800m

downstream but during low flow periods (when the WWTP was treating for P) the

difference between upstream and downstream sites was less and not statistically

significant (see Figures 3.2 and 3.3).

DRP concentrations during low flow periods were within One Plan target values and could

potentially limit periphyton growth at the upstream site and downstream sites. Removal of

phosphorus by the WWTP during periods of low flow reduced median DRP concentrations

in the effluent to 0.018 g/m3 (or 0.098 g/m

3 as a mean) which is similar to the values based

on PNCC monitoring data for the same period.

Total phosphorus was also lower during periods when the WWTP was treating for P and a

statistically significant difference could be detected at 800m downstream but not after full

mixing at 1400m downstream.

Alum used for removing P from the effluent caused an increase in dissolved aluminium

downstream of the discharge during low flow periods. However the absolute concentrations

were low and less than the ANZECC (2000) guideline value even in the effluent prior to

discharge.

Table 3.1: Median water quality results for sites in the Manawatu River during period

November 2011 to May 2012.

Site

EC

(uS/cm)

Field

pH

NH4-N

(g/m3)

TN

(g/m3)

Nitrate

(g/m3)

SIN

(g/m3)

DRP

(g/m3)

TP

(g/m3)

Chl a

(mg/m2)

PPI

(%)

Al

(g/m3)

B

(g/m3)

Cu

(g/m3)

Fe

(g/m3)

Ni

(g/m3)

Zn

(g/m3)

Instream guidelines * 0.900 0.440 0.010 120 / 200 0.0550 0.3700 0.0014 0.0110 0.0080

1000m u⁄s 169.4 7.7 0.01 0.555 0.310 0.320 0.013 0.026 3.9 0.7 0.023 0.021 0.0005 0.061 0.0003 0.0005

800m d⁄s 180.6 7.6 0.17 0.77 0.330 0.525 0.019 0.049 33.5 20.2 0.026 0.022 0.0005 0.06 0.0003 0.0006

1400m d⁄s 174.5 7.7 0.099 0.695 0.310 0.464 0.016 0.040 34.6 10.1 0.022 0.021 0.0005 0.064 0.0003 0.0007

WWTP post wetland 710 29 34 0.007 29.007 2.100 3.100 0.045 0.048 0.002 0.096 0.002 0.017

WWTP pre-wetland 730 30 35 0.007 30.002 2.100 3.000 0.047 0.048 0.002 0.092 0.002 0.017

Metals are dissloved fractions

NZ Periphyton guidelines (Biggs 2000) set limits for SIN of <0.29 g/m3 and DRP of <0.026 g/m3 assuming 20 days accrual period.

12

This is equivalent to the values in the periphyton guidelines assuming a 27 day accrual period.


2-34129.00

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Table 3.2: Median water quality results when Manawatu River flow was less than 40 m3/s

(period November 2011 to May 2012).

Site

EC

(uS/cm)

Field

pH

NH4-N

(g/m3)

TN

(g/m3)

Nitrate

(g/m3)

SIN

(g/m3)

DRP

(g/m3)

TP

(g/m3)

Chl a

(mg/m2)

PPI

(%)

Al

(g/m3)

B

(g/m3)

Cu

(g/m3)

Fe

(g/m3)

Ni

(g/m3)

Zn

(g/m3)

Instream guidelines * 0.900 0.440 0.010 120 / 200 0.0550 0.3700 0.0014 0.0110 0.0080

1000m u⁄s 193.7 7.8 0.008 0.41 0.215 0.228 0.006 0.014 41.3 1.6 0.005 0.022 0.0003 0.0435 0.0002 0.0002

800m d⁄s 202 7.7 0.23 0.7 0.225 0.495 0.008 0.018 225.9 41.2 0.0195 0.0225 0.0003 0.0395 0.0002 0.0005

1400m d⁄s 199.1 8.0 0.16 0.61 0.220 0.427 0.007 0.017 93.9 22.1 0.017 0.022 0.0003 0.04 0.0002 0.0003

WWTP post wetland 750 33 37 0.008 33.01 0.018 0.960 0.049 0.0425 0.0003 0.0435 0.0016 0.0135

WWTP pre-wetland 770 33 37 0.022 33.02 0.030 0.910 0.0645 0.0455 0.0003 0.05 0.0017 0.0135

Metals are dissloved fractions

NZ Periphyton guidelines (Biggs 2000) set limits for SIN of <0.29 g/m3 and DRP of <0.026 g/m3 assuming 20 days accrual period.

Table 3.3: Results of Mann-Whitney non-parametric statistical test comparing upstream

and downstream sites. Bold values <0.005 indicate a statistically significant difference.

Variable All data Flow <40 m3/s All data Flow <40 m3/sConductivity 0.069 0.151 ns ns

Field pH 0.155 ns ns 0.086

NH4-N <0.0001 0.0002 <0.0001 0.0002TN 0.001 0.002 0.076 0.013Nitrate ns ns ns ns

SIN 0.0003 0.003 0.020 0.002DRP 0.008 ns 0.089 ns

TP 0.037 0.041 ns 0.176

Periphyton biomass (Chl a) 0.069 0.017 0.109 0.045Periphyton cover (PPI) 0.0002 0.001 0.013 0.008Cyanobacteria cover % <0.001 <0.001 0.030 0.010Dissolved Al 0.181 0.0002 ns 0.0002Dissolved B ns ns ns ns

Dissolved Cu ns ns ns ns

Dissolved Fe ns ns ns ns

Dissolved Ni ns ns ns ns

Dissolved Zn ns 0.167 ns ns

ns = not statistically significant

p -values are shown where they are less than 0.02.

p-values <0.05 were considered statistically significant.

upstream vs. 1400m downstreamupstream vs. 800m downstream


2-34129.00

13/09/2012 29

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1000m u/s 800m d/s 1400m d/s

DR

P (g

/m3 )

SIN

(g/m

3 )

SIN

DRP

.

Figure 3.2: Mean DRP and SIN in the Manawatu River during period Nov 2011 to May

2012. Error bars show maximum and minimum values. The red line indicates mean

monthly values to control periphyton growth assuming 27 day accrual period (Biggs 2000).

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1000m u/s 800m d/s 1400m d/s

DR

P (g

/m3 )

SIN

(g/m

3 )

SIN

DRP

.

Figure 3.3: Mean DRP and SIN for sites in the Manawatu River during period when river

flow was < 40 m3/s (i.e. WWTP was treating for phosphorus). Error bars show maximum

and minimum values. The red line indicates mean monthly values to control periphyton

growth assuming a 27 day accrual period (Biggs 2000).


2-34129.00

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3.3.3 Potential for nutrient limitation

The potential for nutrient limitation of periphyton growth can be estimated by comparing

both the concentration of SIN to DRP with guidelines of when each nutrient starts to

become limiting as is done in Figure 3.4 and 3.5 for measurements at < half median river

flow and between half median flow and two times median flow. Note that the guidelines for

assessing nutrient limitation given in these graphs are applicable to mean monthly values

and there will be a graduation in the degree of nutrient limitation. Nevertheless the graphs

help illustrate that, based on nutrient concentrations at high flows there was little possible P

limitation for a small percent of time at the upstream site but no limitation at the

downstream sites. During periods of low flow, when the WWTP is treating for P, there was

potential P limitation or co-limitation occurring most of the time at the upstream site, and

potential P limitation occurring 60% to 70% of the time at the downstream sites. The

degree to which nutrients were actually limiting periphyton growth is discussed in the

following sections of this report.


2-34129.00

13/09/2012 31

Manawatu River upstream

Potential limitation status

percentage of results

Unlimited = 67%

N limited = 0%

P limited = 33%

Co-limited = %0

Manawatu River 800m downstream Potential limitation status


Unlimited = 100%

N limited = 0%

P limited = 0%

Co-limited = 0%

Manawatu River 1400m downstream Potential limitation status


Unlimited = 81.25%

N limited = 0%

P limited = 18.75%

Co-limited = 0%

Figure 3.5: Potential nutrient limitation when Manawatu River flow is between half median

flow and two times median flow.

0.0 0.5 1.0

0.00

0.01

0.02

0.03

0.04

0.05

0.06

UnlimitedN LimitedP LimitedCo-Limited

DR

P c

oncentr

ation g

/m3

SIN concentration g/m3

0.0 0.5 1.0

0.00

0.01

0.02

0.03

0.04

0.05

0.06


DR

P c

oncentr

ation g

/m3


0.0 0.5 1.0

0.00

0.01

0.02

0.03

0.04

0.05

0.06


DR

P c

oncentr

ation g

/m3



2-34129.00

13/09/2012 32

0.0 0.5 1.0

0.00

0.01

0.02

0.03

0.04

0.05

0.06


DR

P c

oncentr

ation g

/m3


Manawatu River upstream



Unlimited = 0%

N limited = 0%

P limited = 57%

Co-limited = 43%

0.0 0.5 1.0

0.00

0.01

0.02

0.03

0.04

0.05

0.06


DR

P c

oncentr

ation g

/m3


Manawatu River 800m downstream



Unlimited = 29%

N limited = 0%

P limited = 71%

Co-limited = 0%

0.0 0.5 1.0

0.00

0.01

0.02

0.03

0.04

0.05

0.06


DR

P c

oncentr

ation g

/m3


Manawatu River 1400m downstream



Unlimited = 33.3%

N limited = 0%

P limited = 66.6%

Co-limited = 0%

Figure 3.4: Potential nutrient limitation when Manawatu River flow is less than half median

flow.


2-34129.00

13/09/2012 33

3.3.4 DRP predicted compared to measured

The synoptic surveys identified that groundwater seepage may be contributing to the

nutrient load (and particularly DRP) downstream of the discharge during periods of low

flow. To further investigate this possibility we estimated dilution and DRP concentrations at

site 800m downstream of the discharge during low flow periods (Manawatu River flow < 40

m3/s) using changes in electrical conductivity and same method as described in Section 2.

For the site 800m downstream predicted median DRP during low flow periods (n=10) was

0.0057 g/m3 compared to a measured concentration over the same period of 0.008 g/m

3.

This predicted DRP was only 4% higher than measured upstream concentrations of 0.0055

g/m3 while the measured median concentration was 50% higher. This adds weight to the

conclusions of the synoptic survey. The differences between predicted and measured

values were not statistically significant using the Mann-Whitney test. However testing the

data using a cumulative binomial distribution returned a binomial distribution probability of

0.945, i.e. about 5% probability that the predicted DRP was lower than the measured DRP

due to chance13

.

3.4 Summary

During low flow periods DRP and SIN reduced to concentrations that could

potentially control periphyton growth at the upstream site. However, at the

downstream sites only DRP was sufficiently low to potentially control periphyton

growth during low flow periods.

Total ammonia and SIN concentrations were significantly higher at downstream

sites under all flow conditions.

DRP and TP concentrations were significantly higher at the downstream sites when

the WWTP was not removing P from the effluent. Removal of phosphorus by the

WWTP during periods of low flow reduced the median DRP concentration in the

effluent to 0.018 g/m3 (or 0.098 g/m

3 as a mean). DRP concentration at the

downstream site was still higher than upstream but the difference was not

statistically significant.

Treating for P also elevated dissolved aluminium at the downstream site but the

absolute concentrations remained low relative to the ANZECC guideline value.

Predicted DRP based on dilution of the effluent during all low flow periods (n=10)

was less than measured values and only 4% higher than upstream values, while

measured values were 50% higher; adding weight to conclusion of the synoptic

survey that there was another source of DRP downstream of the discharge.

13

Based on predicted values being less than measured values 7 times out of 10.


2-34129.00

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4 Periphyton dynamics

4.1 Aim

Weekly monitoring of periphyton cover and biomass was undertaken to improve our

understanding of periphyton temporal dynamics, variability in space and time, how quickly

periphyton cover/biomass increases after floods, and how much periphyton growth occurs

before and after the discharge is treated for P. The key aims of this monitoring were to:

To clarify the extent to which the Totara Road WWTP discharge was affecting

periphyton growth in the Manawatu River.

To inform any decision to refine the timing of wastewater phosphorus removal in

order to limit downstream periphyton growth.

4.2 Method

Periphyton monitoring was undertaken weekly from 16th November 2011 to 25

th May 2012

at the same time as water quality sampling. The sampling was usually done on a

Wednesday or Thursday.

Samples were collected from the same river monitoring sites as water quality samples:


Manawatu River about 800m below the discharge point; and

Manawatu River about 1400m below the discharge point (commenced in week 5 of

the sampling programme).

All sites were at the upstream side of a gravel beach and had similar conditions in terms of

lighting, clarity, water depth, water velocity and substrate size.

The monitoring involved visual estimates of periphyton cover in runs and collecting a

representative sample for analysis of chlorophyll a and species composition. Where

cyanobacteria mats were present, an additional sample was collected and analysed for

toxicity14

.

The method for periphyton assessment was:

1. A visual assessment of the percentage cover of filamentous algae, algal mats,

„sludge‟, „films‟ and „clean‟ at 5 points across each of 10 transects (4 transects at

1400m downstream) encompassing run habitat and extending across the wadable

width of the river (i.e. to a maximum depth of about 0.6m). The first transect

location was marked to allow sampling at a similar location each week. The

transects were at least 5 metres apart.

14

Toxicity analysis contributed to additional investigations being undertaken by Horizons Regional Council.


2-34129.00

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2. The visual monitoring methods followed the protocols outlined in Appendix 2 of “A

periphyton monitoring plan for the Manawatu-Wanganui Region” (Kilroy et al. 2008).

Reported estimates included the following categories:

percentage cover of visible river bed by bacterial and/or fungal growths

(sewage fungus) visible to the naked eye;

percentage cover of visible river bed by slimy filamentous algae more than 2 cm

long;

percentage cover of visible river bed by coarse filamentous algae greater than

2 cm long;

percentage cover of visible river bed by diatoms mats more than 0.3 cm thick ;

percentage cover of visible river bed by cyanobacteria mats more than 0.3 cm

thick;

percentage cover of visible river bed by film (typically diatoms) less than 0.3 cm

thick; and

percentage cover of visible river bed that is clean.

3. The collection of a periphyton biomass sample at the same established monitoring

sites and transects as above, using method QM-1b from the Stream Periphyton

Monitoring Manual (Biggs & Kilroy 2000). This involved removing all periphyton

from a 5.0 cm diameter area on the surface of ten (10) rocks collected across a

single transect and the samples bulked to produce a single sample (i.e. a total area

sampled of 0.02 m2). Samples were frozen and sent to NIWA for analysis of

chlorophyll a and species composition (using quantitative 200 fixed counts).

Analysis of periphyton samples followed the Biggs & Kilroy (2000) guidelines for

chlorophyll a analysis.

4. The substrate type, water depth and water velocity were recorded using the ruler

method (see Harding et al 2009) at each point where samples are collected along

the transect.

5. Additional information was collected including the distance from the marker stake to

the water line and an estimate of the percent cover of any periphyton exposed

above the water line. River substrate were photographed on each occasion.

6. A sample of cyanobacteria (if present) was collected at each site and sampling

occasion by scaping mat material from 10 rocks into a plastic container. The

samples was frozen as soon as possible and then sent for toxin extraction and

analysis.

To help assess the biological health of the river, the following ecological indices were

calculated based on Collier et al. (2007):


2-34129.00

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Periphyton Proliferation Index (PPI). This is an indicator of biomass. It is the percent

cover of long filaments algae (>2cm) and diatom + cyanobacteria mats (>0.3cm).

Periphyton Slimyness Index (PSI). This is an indicator of biomass and is the

weighted percent cover of each thickness category. We used a modified calculation

because our method grouped „median‟ and „thick‟ mats; it was calculated as: PSI =

{(%Thin mat <0.3cm) + (%mats 0.3-3cm * 2) + (% Slimy filamentous >2cm * 4) +

(Coarse filamentous >2cm and %cyanobacteria mat*5)} / 5.


The results of weekly periphyton monitoring during November 2011 to May 2012 are shown

in Appendix 4. The median values of periphyton biomass and cover are shown in Tables

3.1 and 3.2, and the results of the statistical test shown in Table 3.3.

Periphyton biomass (as measured by chlorophyll a) and periphyton cover (as measured by

the Periphyton Proliferation Index (PPI) were within POP trigger values (and guideline

values) at the upstream site but exceeded these values at the downstream sites (see

Figure 4.1). Both periphyton cover and biomass were significantly higher at the two

downstream sites compared to the upstream site during low flow periods.

As expected, there was a strong correlation between periphyton cover and periphyton

biomass (see Figure 4.2). For the site 800m downstream the relationship became non-

linear at high biomass – possibly due to co-correlation with more filamentous green algae

(with more chlorophyll a) at higher biomasses . Another interesting feature was that the

relationship between the two measures appeared to be different at different sites. At a

biomass of 120 mg chlorophyll a /m2, periphyton cover was estimated to be about 14% at

the upstream site and about 28% at the site 800m downstream. The relationship at the

downstream site corresponds better to the corresponding values in the NZ periphyton

guidelines (Biggs 2000). It is not clear why relative estimates of cover and biomass differed

between the sites – it could be because the method for estimating cover did not distinguish

long strands of diatoms from thicker filamentous green algae. The rest of this section

focuses on relationships based on periphyton biomass because biomass correlations

between accrual period and biomass were stronger than correlations based on cover (PPI)

(e.g. for the upstream site the r2 = 0.70 for PPI verse days since last flood, compared to a

r2 of 0.93 for chlorophyll a verse days since last flood).

4.3.1 Periphyton species

The periphyton species that numerically dominated samples were the diatoms

Gomphonema sp., Rossithidium sp., Melosira varians, Diatom sp., Rhoicosphenia sp., and

the filamentous green algae Stigeoclonium sp. Diatoms were consistently most dominant

after periods of flood and the filamentous green algae Stigeoclonium sp. become more

dominant during periods of low flow – especially at the site 800m downstream. A

comprehensive analysis of changes in species composition has not been undertaken.

All sites had only a small proportion of cyanobacteria cover during the monitoring period.

When cyanobacteria species were present they were mostly Phormidium sp. or

Leptolyngbya sp. with Oscillaroria sp. less common. The maximum cyanobacteria cover


2-34129.00

13/09/2012 37

recorded at the upstream site and 1400m downstream site was less than 1% (0.7% and

0.3% respectively). The site 800m downstream had a mean of 3% cover of cyanobacteria

with a maximum cover recorded of 8.6%. Cyanobacteria cover between sites was

statistically significant (see Table 3.2), however the overall cover was much less than the

20-50% trigger levels in the cyanobacteria guidelines (MfE and MoH 2009).

More cyanobacteria cover (albeit small) is consistent with what would be expected due to a

higher N:P ratio found downstream of the discharge and higher absolute nutrient

concentrations. Horner et al. (1990) found that diatoms were favoured by relatively high

velocities and low phosphorus concentrations, whereas the blue-green algae Phormidium

tend to be dominate at higher DRP concentrations. Green algae preferred higher DRP and

lower velocities.

No cyanotoxins were found in the cyanobacteria samples but in two out of six samples

where cyanobacteria were present the sampling analysis found trace amounts of dihydro-

homoanatoxin-a which is a degradation product of anatoxin-a. The concentrations present

on these occasions were very low compared to concentrations found by Wood et al. (2010)

in a survey of 7 rivers throughout NZ or by Wood and Young (2011) in a survey of benthic

of cyanobacteria in Manawatu Rivers.

0

20

40

60

80

100

120

0

100

200

300

400

500

600

1000m u/s 800m d/s 1400m d/s

Perip

hyto

n Pr

olife

ratio

n In

dex

(%)

Perip

hyto

n bi

omas

s (m

g C

hl a

/m3 )

Periphytonbiomass

PPI

.

Figure 4.1: Mean periphyton biomass and cover measured during periods of low flow (<40

m3/s). Error bars indicate maximum and minimum values. The red line indicates guideline

values for biomass and cover for filamentous green algae (Biggs 2000).


2-34129.00

13/09/2012 38

R² = 0.8118

R² = 0.8571

0

10

20

30

40

50

60

70

80

90

0 100 200 300 400 500 600

Perip

hyto

n Pr

olife

rato

in In

dex

(%)

Periphyton biomass (mg Chl a/m2)

upstream

800mdownstream

1400mdownstream

Figure 4.2: Relationship between periphyton biomass and periphyton cover as measured

by the Periphyton Proliferation Index.

4.3.2 River flow as a controlling factor in periphyton biomass

Figure 4.3 shows that change in periphyton biomass at each site during the summer

monitoring. It shows more rapid growth and higher periphyton biomass at the downstream

sites with declines in periphyton biomass driven by flow events.

The relationship between periphyton biomass and flow is illustrated in Figures 4.4 and 4.5.

Flood flows greater than three times the median flow15

often approximates the level of flow

to move bed sediment and remove periphyton biomass (e.g. Clausen and Biggs 1997).

During this study even a 2x median flow (about 146 m3/s) reduced biomass to less than 1

mg chl a /m2

(see Figure 4.4). The correlation between periphyton biomass and days

since a 3x median flow flood had an r2 of 0.93 and 0.83 for the upstream and 800m

downstream site respectively. There was a slightly better correlation with a 2x median flow

and generally there was only one or two days difference between accrual periods

calculated with a 2x median flow event and accrual due to a 3x median flow event.

High velocities caused by high flow reduced periphyton biomass through scour. Loss rates

increase with increasing suspended sediment due to addition scour effects but also with

additional biomass. An elevation of velocity above which periphyton is accustomed can

lead to increased loss rates and temporarily reduce biomass (Horner et al. 1990); this

15

About 219 m3/s in the Manawatu River at Teaches College.


2-34129.00

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probably explains occasional dips in biomass (e.g. on 3rd May at 800m downstream)

associated with only small flow increases.

Not only did periphyton biomass increase with the days of accrual since the last flood but

so did the rate of periphyton accrual (see Figure 4.6). The rate of periphyton growth was

much faster at the 800m downstream site compared to the upstream site but at both sites

growth rate increased over time. This was partially because the rate of increase (measured

as mg chl a /m2/day) was strongly associated with the initial periphyton biomass (see

Figure 4.7). The higher the initial biomass the faster the periphyton growth rate up to the

point where periphyton biomass was sufficiently high (i.e. above about 200 mg/m2) (or

thick) so that growth rates slow. Periphyton at the site 1400m downstream appeared to

slough off and scour at lower biomass levels compared to the site 800m downstream.

If periphyton biomass accrual is expressed as a percentage change of the initial biomass

then the highest percentage increase in periphyton biomass was observed when the initial

biomass was low, however the r2 values for this correlation were very poor (e.g. about

0.14).

There was no positive relationship between nutrients and periphyton biomass or growth. In

fact there was a weak negative log-log relationship between DRP concentration and

periphyton biomass (r2 =0.66 at upstream site and r

2 =0.48 at 800m downstream site).

Similarly there was a weak negative log-log relationship between DRP concentration and

periphyton accrual. This reflects background nutrient concentrations in the river declining at

all sites as the river recedes after a flood (possibly due in part to uptake by periphyton).

0

100

200

300

400

500

600

Perip

hyto

n bi

omas

s (m

g C

hl a

/m2 ) upstream

800m downstream

1400m downstream

3x median flow events

Figure 4.3: Change in periphyton biomass over time during the summer 2011-2012


2-34129.00

13/09/2012 40

0

5

10

15

20

25

30

35

40

0 50,000 100,000 150,000 200,000 250,000

Pe

rip

hyt

on

bio

mas

s (m

g C

hl a

/m2)

Manawatu River flow (l/s)

upstream

800m downstream

1400m downstream

Power (upstream)

Figure 4.4: Periphyton biomass in relation to flow in the Manawatu River (Nov 2011 – May

2012) (scales are truncated).

y = 0.1812x2 - 4.3651x + 33.34R² = 0.9296

y = 14.577x - 123.12R² = 0.8341

0

100

200

300

400

500

600

0 10 20 30 40 50

Pe

rip

hyt

on

bio

mas

s (m

g C

hl a

/m2)

Days since 3x median flow

upstream

800m downstream

1400m downstream

Upstream trend

800m downstream trend

Figure 4.5: Periphyton biomass increasing with increasing number of days of accrual. Data

limited to periods of accrual.


2-34129.00

13/09/2012 41

y = 0.2495x - 2.163R² = 0.6251

y = -0.0203x2 + 1.9858x - 14.425R² = 0.7802

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50

Pe

rip

hyt

on

acc

rual

(m

g C

hl a

/m2/d

ay)

Days since 3x median flow

upstream

800m downstream

1400m downstream

upstream trend

800m d/s trend

Figure 4.6: Periphyton accrual rate increasing with the number of days of accrual. Data

restricted to periods of accrual and positive accrual rates.

y = 0.6012x0.6003

R² = 0.5012

y = 3.7348ln(x) + 9.4862R² = 0.936

y = 0.4565x0.46

R² = 0.3517

0

5

10

15

20

25

30

35

0 100 200 300 400

Pe

rip

hyt

on

acc

rual

(m

g C

hl a

/m2/d

ay)

Periphyton initial biomass (mg Chl a/m2)

upstream

800m downstream

1400m downstream

Power (upstream)

Log. (800m downstream)

Power (1400m downstream)

Figure 4.7: Periphyton accrual rates compared to initial biomass in the Manawatu River


2-34129.00

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4.3.3 Frequency of exceeding periphyton biomass guidelines

The relationships derived from Figure 4.5 can be used to estimate the number of days

since a 3x median flow flood for periphyton to exceed the diatom guideline value of 200 mg

chl a/m2 in the Manawatu River. On average it took about 44 days, 22 days and 25 days to

exceed guideline value for the upstream site, 800m downstream site and 1400m

downstream site respectively. Flow data from the Manawatu River at Teachers College

from a 21 year period (1987-2008) was used to estimate the frequency of flood events and

accrual periods during the summer (1 November to 30 April) (for details see McConchie

2009). Over this 21 year period the frequency of accrual periods exceeding 22, 25 and 44

days during the summer were respectively 1.65 times per summer, 1.51 times per summer

and 0.78 times per summer. The median length of time for which the accrual period

exceeded 22 days per summer, 25 days per summer and 44 days per summer were

respectively 19 days, 24 days and 34 days.

Thus, using the relationship between periphyton biomass and days accrual since the last

flood (3 times median flow) it was estimated that the 200 mg/m2 guideline for periphyton

biomass would (on average) be exceeded at the upstream site 0.78 times per summer for

a median period of 34 days; at the 800m downstream site 1.65 times per summer for a

median period of 19 days; and at the 1400m downstream site 1.51 times per summer for a

median period of 24 days.

The One Plan sets a periphyton biomass guideline for the Manawatu River of 120 mg/m2 –

equivalent to the filamentous algae guideline. It took 37 days, 17 days and 19 days to

exceed this biomass for the upstream site, 800m downstream site and 1400m downstream

site respectively. This corresponds to an exceedance frequency of 1.06 times per summer,

1.93 times per summer and 1.70 times per summer for the upstream site, 800m

downstream site and 1400m downstream site respectively.

It should be noted that periphyton biomass can be reduced by flows much less than a three

times median flow flood. The relationship between periphyton biomass and days accrual

since 3x median flow flood excluded data where smaller floods cause a reduction in

periphyton biomass, extending the method to estimate a total number of days guidelines

are exceeded is likely to be an over-estimate.

Francis and Death (2001) monitored periphyton weekly during low flows during the

summers of 1999/2000 and 2000/2001. They found rapid periphyton growth downstream of

the WWTP discharge which exceeded guideline values after only 7 to 10 days of accrual,

while the upstream sites took 25 to 40 days to exceed the 120 mg/m2 guideline value.

David Cameron (in evidence presented for the Totara Road WWTP hearing) used this data

to estimate that after upgrading the WWTP to remove P during low flow periods (median

DRP of 0.015 g/m3 in the discharge) periphyton would require 18 days to exceed the

guideline. This is very similar to the mean accrual period of 17 to 19 days for the

downstream sites (Figure 4.5), suggesting that evidence presented about the frequency

and duration of effects on periphyton was reasonable.


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4.3.4 Periphyton growth rates during the April low flow period

During the six months of monitoring the only extended period of low flow occurred in April

and into May. Changes in periphyton biomass, biomass accrual and percent accrual are

shown in Figures 4.8 and 4.9. A large flood (607 m3/s) occurred on 21

st March with flow

dropping below three times median flow on 23rd March. Turbidity in the river remained high

for a number of days and dropped below 12 FTU (about 38cm water clarity16

) on 28th

March. The Manawatu River flow at this time was about 60 m3/s. Another small flood

occurred on 6th April elevating the turbidity for four days from 4

th to 8

th of April. After this the

flow steadily receded until a small fresh on 29th April elevated flows to 62 m

3/s (less than

median flow), and another on 15th May (about 2 times median flow). The WWTP was

removing P from the effluent from 1st to 3

rd April, 11

th-12

th April, 14

th to 30

th April and 2

nd to

14th May. The mean nutrient concentration in the stream during the March-May low flow

period is shown in Table 4.1.

The increase in periphyton biomass (Figure 4.8) followed a sigmoid curve at all sites, with

little initial change followed by a period of rapid accumulation with the rate of accumulation

then reducing at over time. The downstream sites showed substantially more biomass

accrual compared to upstream. The greatest increase in periphyton biomass occurred at

the site 800m downstream, followed by 1400m downstream. Photos in Appendix 1 illustrate

this change in cover over the period of April to May.

Graphs of biomass accrual in Figure 4.9 can be understood as showing the „velocity‟

periphyton growth with a steeper gradient indicating more „acceleration‟ in the growth rate.

The rate of biomass accrual steadily increased over the period until the small fresh on 29th

April which probably increased sloughing of algae from the two downstream sites that had

high biomass. In terms of percent change the highest accrual rates at the downstream sites

occurred early in the growth period between 5th and 11

th of April (see Figure 4.9).

Although the maximum rate of periphyton accumulation was similar between the sites

800m downstream and 1400m downstream; the initial phase of periphyton growth (before

11th April) was much more rapid at the site 800m downstream compared to the sites 1400m

downstream and upstream. This suggests some factor was stimulating (“kick-starting”) the

initial phases of periphyton growth so that it entered a rapid growth phase about a week

before the other sites.

Fungus was found scattered through the 800m downstream sample on 28th March and it is

possible that labile organic carbon in the discharge promoted more rapid development of

heterotrophic biofilms (consisting of fungus and bacteria) at the site 800m downstream and

that „conditioned‟ the substrate for more rapid periphyton growth. Fungus can promote the

release of phosphorus from sediments (Palmer-Felgate et al. 2010). Ardón and Pringle

(2007) found that labile organic carbon stimulated the development of biofilms in streams

and magnified the stimulatory effect of phosphorus enrichment on biofilm activity.

16

Black disk water clarity was calculated from 15 minute turbidity measurements at the Teachers College

site. A correlation between black disk and turbidity (in FTU) was derived using data from 2006 to 2012,

where: black disk distance (m) = 2.2143 [turbidity]-0.706

. R2=0.91


2-34129.00

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The change in periphyton biomass on the bioassay is also shown in Figure 4.8. Although

shown as a straight line periphyton growth on the bioassays would have also followed a

sigmoid curve17

. The lines labelled “a” shows the gradient equal to the change in periphyton

biomass on the bioassay site “d/s D”. The rate of change of the downstream bioassay over

two weeks was similar to that observed for the first two weeks of growth at the site 800m

downstream (assuming that periphyton accumulation started about 4th April

18). Interestingly

the bioassay at the upstream site had a considerably higher rate of growth compared to

that observed for the first two weeks of growth in the stream.

Table 4.1: Mean nutrient concentrations during the period 28th March to 25 May 2012

(n=8).

All flows River flow >40 m3/s River flow <40 m3/s

Site DRP (g/m3)

SIN (g/m3)

DRP (g/m3)

SIN (g/m3)

DRP (g/m3)

SIN (g/m3)

Upstream 0.0089 0.254 0.011 0.31 0.0075 0.22

800m d/s 0.0137 0.467 0.020 0.44 0.0097 0.483

1400m d/s 0.012 0.391 0.015 0.39 0.01 0.393

Effluent post-wetland 1.17 32.5 2.7 30.3 0.025 34.1

17

The five day bioassay had less than 2 mg/m2 after five days.

18 Periphyton biomass at 800m downstream was 0.6 mg/m

2 on 5

th April. This is similar to biomass on the

bioassay after 5 days of growth (suggesting growth started about 31st March but algae growth would have

been delayed about four days by elevated turbidity from 4th to 8

th of April.


2-34129.00

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0

100

200

300

400

500

600Pe

riphy

ton

biom

ass

(mg

Chl

a /m

2 ) upstream

800m downstream

1400m downstream

Bioassay u/s A

Bioassay d/s C

Bioassay d/s D

rain, lifts flow to 60m3/s

112 m3/s flood 6th April

Flood 3x median flow on 23rd March

a

Figure 4.8: Periphyton biomass in the Manawatu River during receding river flows in April

2012. Line “a” shows the gradient equal to the change in periphyton biomass on the

bioassay sites “d/s D”.


2-34129.00

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-10

-5

0

5

10

15

20

25

30

35Pe

riphy

ton

accr

ual (

mg

Chl

a /m

2 /d

ay)

upstream

800m downstream

1400m downstream

Bioassay u/s A

Bioassay d/s C

Bioassay d/s D

small freshsmall fresh

P removed from 11th April

0%

200%

400%

600%

800%

1000%

1200%

Perip

hyto

n ac

crua

l (%

/day

) upstream

800m downstream

1400m downstream

small fresh

Figure 4.9: Periphyton biomass accrual and % accrual in the Manawatu River during

receding river flows in April 2012.


2-34129.00

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4.3.5 Comparison of April periphyton growth and model predictions

The phosphorus regression model described in Biggs (2000) was applied to the data for

the purpose of examining the possible reasons for elevated periphyton growth at the

downstream site. The regression model predicts maximum chlorophyll a concentrations as

a function of mean days of accrual and mean monthly DRP using data from 30 New

Zealand rivers. This model will, at best, be approximate when applied to a specific river, but

it is helpful for examining the effects of DRP and extending the number of day of accrual. It

is also helpful to apply because it forms the basis of the nutrient guidelines for periphyton in

Biggs (2000).

The results of applying different scenarios to the model are shown in Table 4.2. The first

scenario (i.e. April DRP, accrual from flood event) applies the model using the most

realistic data for the March-April period. It uses mean DRP concentrations for the period

28th March to 25

th May and an accrual period based on time elapsed from the end of the

flood event that exceeded more than three times median flow. This is the definition of

accrual period used for data used for developing the model (Biggs 2000 b).

The results show that for the growth period up to 24th April, the upstream sites had

considerably less periphyton biomass compared to what was predicted by the model, the

800m downstream site had considerably more periphyton and the 1400m downstream site

was similar to the predicted periphyton biomass.

A shorter, 20 day accrual period (starting 4th April) reflects a best estimate of when accrual

actually did start in the section of the river being monitored considering the constraints of

elevated turbidity and the low flow DRP is based on the median DRP concentration during

low flow periods during the summer. Although not the most appropriate period or

concentration to apply to the model, it allows us to investigate the sensitivity of periphyton

growth to a shorter accrual period and a lower DRP concentration. Under each of these

scenarios the periphyton biomass at the upstream site remained less than model

predictions, suggesting that some factor other than DRP concentrations was controlling

periphyton growth at the upstream site.

The scenarios with high DRP concentrations used the mean DRP during the monitoring

period when flows were between 40 m3/s and 110 m

3/s. This reflects concentrations when

there was no phosphorus removal and over-estimates the actual DRP concentrations

during the April growth period. Under these scenarios the model continued to under-

estimate the actual periphyton biomass at the site 800m downstream but approximately

predicted measured biomass at the site 1400m downstream (assuming a 30 day accrual

period). This adds weight to the previous observation that some factor(s) were either

stimulating or kick-starting periphyton growth at the site 800m downstream. The magnitude

of this effect is sufficiently strong that we were measuring more periphyton than could be

explained by the model if no P treatment was occurring.


2-34129.00

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Table 4.2: Predicted verses actual chlorophyll a concentrations for different assumptions of

accrual period and DRP. Chlorophyll a was modelled using the equation in Biggs (2000).

Scenario site Date

Measured

Chl a

(mg/m2)

Predicted

max Chl a

(mg/m2)

accrual

period

DRP

(mg/m3)

April DRP, accrual from flood event u/s 24-Apr 75 222 30 8.9

April DRP, accrual from flood event 800 d/s 24-Apr 418 275 30 13.7

April DRP, accrual from flood event 1400 d/s 24-Apr 277 257 30 12

April DRP, 20 day accrual u/s 24-Apr 75 110 20 8.9

April DRP, 20 day accrual 800 d/s 24-Apr 418 136 20 13.7

April DRP, 20 day accrual 1400 d/s 24-Apr 277 128 20 12

Low flow DRP, 30 day accrual u/s 24-Apr 75 183 30 6

Low flow DRP, 20 day accrual u/s 24-Apr 75 91 20 6

High DRP, 20 day accrual 800 d/s 24-Apr 418 187 20 26




30 day accrual period based on accrual starting after flood ending 25th March.

April DRP concentrations based on 8 measurements between 28 March - 25 May.

High DRP based on average if no treatment (using flow 40 m3/s > 110 m3/s)

Low DRP based on median DRP during summer when flows < 40 m3/s

4.4 Summary

During periods of low flow periphyton biomass and cover were higher downstream

of the discharge than upstream and exceeded guidelines values.

There was more cyanobacteria (Phormidium sp.) cover at the 800m downstream

site than at the upstream and 1400m downstream sites, but overall there was very

little cyanobacteria present (less than 3% cover at the site 800m downstream).

Periphyton cover was strongly controlled by flow in the Manawatu River. Flow of 2

to 3 times median flow were generally sufficient to reduce periphyton biomass to

very low levels – particularly if they occurred for an extended period of time.

The rate of periphyton growth increased with the length of time it had to grow up to

the point where periphyton biomass exceeded about 200 to 300 mg/m2 so that loss

due to sloughing balanced (or exceeded) in growth.

On average it took about 37 days, 17 days and 19 days to exceed the 120 mg/m2

filamentous algae guideline values for the upstream site, 800m downstream site

and 1400m downstream site respectively. When compared to 21 years of flow data

during summer (1 November to 30 April) these correspond to frequencies of: 1.1

times per summer; 1.9 times per summer; and 1.7 times per summer for each site

respectively.


2-34129.00

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The accrual period at the downstream sites are similar to those predicted by in

evidence presented at the hearing for the WWTP current consent.

During the April low flow period the downstream sites showed substantially more

biomass accrual compared to upstream. The greatest increase in periphyton

biomass occurred at the site 800m downstream. Periphyton growth at all sites

followed a sigmoid curve.

The initial phase of periphyton growth (while biomass was still relatively low) was

much more rapid at the site 800m downstream compared to the other sites. This

would be consistent with more rapid development of heterotrophic biofilms

stimulating the initial phases of periphyton growth allowing more rapid growth to

occur sooner and possibly increasing nutrient cycling.

A simple regression model (from Biggs 2000) was used to predict periphyton

biomass in April and examine sensitivity to changes in nutrients and accrual period.

Upstream periphyton biomass was considerably less than those predicted by the

model, even when accrual period and DRP concentrations were reduced. This

suggested that some factor other than DRP concentrations was controlling

periphyton growth at the upstream site.

The 800m downstream site had considerably more periphyton biomass than

predicted by the model and the 1400m downstream site had a similar biomass. A

scenario assuming high DRP concentrations typical of no phosphorus treatment still

underestimated the periphyton biomass at the site 800m downstream. This would

be consistent with the theory that dissolved organic carbon form the discharge may

be stimulating development of heterotrophic biofilms which condition substrate for

periphyton colonisation thus reducing the initial accrual period.

Faster growth rates at the site 800m downstream might also be explained by

periphyton experiencing higher DRP concentrations than measured in the water due

as DRP enters the river from groundwater seepage or desorption at the sediment-

water interface (see previous chapter).

The periphyton bioassay at the upstream site had a faster growth rate compared to

the first two weeks of periphyton growth in the river; however the downstream

bioassay had a similar growth rate compared to that observed in the river.


2-34129.00

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5 Nutrient limitation

5.1 Aim

Nutrient concentrations have a significant effect on the rate of periphyton growth. Both

phosphorus and nitrogen are thought to have a controlling influence of periphyton growth in

the Manawatu River with the potential controlling nutrient varying in space and time and

being highly influenced by river flow (McArthur et al. 2010). The WWTP treats for

phosphorus with the aim of reducing any stimulation of periphyton growth. A periphyton

nutrient bioassay was undertaken and measurements of periphyton cellular nutrient

concentrations were made in order to:

Confirm which if any nutrient is limiting periphyton growth upstream and

downstream of the discharge;

Inform any decision to refine the timing and extent of wastewater phosphorus

removal in order to limit downstream periphyton growth.

5.2 Method

5.2.1 Cellular nutrients

Cellular nutrients provide a measure of nutrient limitation. The Redfield ratio (i.e. TN:TP of

7.2:1 by weight) is typically regarded as the optimum ratio of nutrient growth with a higher

ration indicating possible P limitation. There is some evidence that not all periphyton

species follow the Redfield ratio so the optimum cellular N:P ratio was based on the ratio

in periphyton growing with excess N and P (e.g. downstream of the discharge with no P

treatment). If treatment of P by the WWTP is being effective at limiting periphyton growth

we would expect to see an increase in the TN:TP ratio beyond the optimum ratio.

Estimates of periphyton cover were extended to measure replicate cellular N, cellular P

concentrations and relative abundance of periphyton species on the following three

occasions.

25 January 2012 after about two weeks of receding water flow and just before

commencement of phosphorus treatment (i.e. flow just above half median flow).

21 April 2012, after 9 days of the WWTP treating for phosphorus.

28 April 2012 after 16 days of the WWTP treating for phosphorus.

Samples were collected from the same upstream and downstream sites as used for

assessing periphyton cover, i.e. Manawatu River about 1000m above the discharge point;

and Manawatu River about 800m below the discharge point (see Figure 3.1).

On each sample occasion six (6) replicate samples were collected at each site, using

method QM-1b from the Stream Periphyton Monitoring Manual (Biggs & Kilroy 2000). Each

replicate consisted of up to five samples bulked to obtain a minimum of five grams. For

each replicate the following variables were analysed: cellular N and cellular P.


2-34129.00

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A separate sample from each replicate rock was scrapped and collected and sent to NIWA

for analysis of periphyton identification and relative abundance. Subsamples are examined

using an inverted microscope at magnifications up to 400x, and algal taxa present identified

and listed. The relative abundance of each taxon was assessed following the method in

Biggs and Kilroy (2000) on a scale of: 8 =dominant, 7 =abundant; 6 =common-abundant, 5

= common, 4 = occasional-common, 3 = common, 2 = rare-occasional, 1 =rare. For

simplicity we have only listed the most abundant taxa in the results tables (scores 6 to 8) in

order of dominant (8) to common-abundant (6).

Since optimum N to P ratios can vary between periphyton species, attention was given to

sampling the periphyton type that was dominant at the site downstream of the discharge as

opposed to collecting a representative sample. In practice this meant collecting five

replicates of filamentous algae mats and a single sample of cyanobacteria mats if they

were present.

5.2.2 Periphyton nutrient limitation bioassay

A periphyton nutrient bioassay was undertaken using the steel tray nutrient diffusing

substrate method described in Biggs and Kilroy (2000). This used five replicates of four

different treatments:

a) agar with no enrichment (control),

b) nitrogen enriched agar,

c) phosphorus enriched agar, and

d) nitrogen and phosphorus enriched agar.

The agar and nutrient solution was made and stored in a fridge for several weeks prior to

using the trays in the river. They were originally put in the river in late March but had to be

removed on 3 April (after five days) due to a predicted flood event. Just prior to applying

the GFC filter papers and installing in the river for the second time on 14th April, the top

layer of agar was removed and the bottles topped up with fresh agar /nutrient solution.

Two trays were deployed upstream and two downstream of the discharge. The trays were

located close to the upstream and downstream sites as used for assessing periphyton

cover and water quality sampling. One of the upstream trays was stolen from the river

during the experiment so the experiment had data from:


Manawatu River about 800m below the discharge point;

Manawatu River about 880m below the discharge point.

The bioassay was put in the river on 14th April 2012 (when the river reached half median

flow and the WWTP started treating for P) and removed on 27th April 2012 (13 days).


2-34129.00

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The samples from the artificial substrates were sampled for chlorophyll a concentration

(converted to mg/m2).

Before and after installing the bioassays measurements were made of water depth, water

velocity, and the abundance of any snails on substrates. All sites were exposed and had

limited impacts from riparian shading.

Interpretation of the results was complicated by the trays containing the nutrient diffusing

substrates being installed perpendicular to the water flow rather than parallel to the water

flow as described in Biggs and Kilroy (2000). In each case the most upstream treatment

was the N treatment, followed by P, N+P and the control. This error caused the possibility

of the N treatment interfering with the P treatment and both the N and the P treatment

interfering with the control. It also caused the possibility of laminar flow over the trays

causing higher velocities and more turbulence at the downstream end – closest to the

control treatments. Despite these complications useful conclusions can be made from the

results by focusing on comparisons with the N and P treatments and difference between

sites.


5.3.1 Cellular nutrients

The results of cellular nutrient analysis are summarised in Table 5.1 with statistical

comparisons shown in Table 5.2. Results from all replicates are shown in Table 5.3.

Replicates dominated by (or containing significant amounts) of cyanobacteria (i.e.

Phormidium sp) were excluded from the analysis because these samples responded

differently to nutrients from the discharge compared to samples dominated by green

filamentous algae (i.e. Stigeoclonium) or diatoms (e.g. Diatoma tenuis or Melosira varians).

Samples containing Phormidium had higher TN:TP ratios at the downstream site compared

to non-cyanobacteria samples because of a disproportionately greater increase in cellular

N.

The optimum ratio of TN:TP for the periphyton community is indicated by results from

downstream samples, and particularly those collected in January which was a period when

the WWTP was not removing P from the discharge. The results indicate an optimum

TN:TP ratio of 6.3 - 6.4, which is similar to the Redfield ratio of 7.2 (by weight).

The upstream site had a significantly higher TN:TP ratio compared to the downstream sites

on all sample occasions (see Figure 5.1 and Table 5.2) suggesting that periphyton cells

were potentially phosphorus limited. The TN:TP ratio was significantly higher on the 28th

April (9 days of P treatment) compared to the 21st April (16 days of P treatment),

suggesting that the degree of potential P limitation was increasing at the upstream site as

periphyton biomass increased (estimated to change from about 50 mg/m2 to about 120

mg/m2). DRP concentrations in the Manawatu River upstream of the discharge was low

(0.005 mg/l to 0.006 mg/l) in the period 18th to 24

th April).


2-34129.00

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In contrast, the downstream site had no significant difference in the cellular TN:TP ratio

between sampling dates (see Figure 5.1) – suggesting that neither N or P was controlling

periphyton growth at the downstream site even after the two weeks of P removal from the

effluent.

The increase in TN:TP ratio observed at the upstream site was due to a disproportionate

reduction in cellular P compared to cellular N (see Figure 5.1, Tables 5.1 and 5.2). The

reduction in the absolute concentration of cellular TP and (to a lesser extent) TN in

between 21st April and 28

th April could be due to a number of factors, for example Hill and

Fanta (2008) found cellular nutrient concentrations to be highly positively correlated with

specific growth rate.

Table 5.1: Median cellular nutrient concentrations (excluding replicates with Phormidium)

and river water quality grab samples. The WWTP was treating for P during April but not

during January sampling.

Date * Site

TP

(mg/kg)

TN

(mg/kg) TN/TP

River DRP

(mg/l)

River DIN

(mg/l)

25-Jan-12 upstream 1690 15500 8.5 0.007 0.360

25-Jan-12 downstream 3400 26000 6.3 0.012 0.960

21-Apr-12 upstream 4700 36000 7.9 0.007 0.230

21-Apr-12 downstream 5200 33000 6.4 0.018 0.910

28-Apr-12 upstream 2500 32000 12.0 <0.005 0.470

28-Apr-12 downstream 4500 31000 6.4 0.011 0.540

* Water qualtiy grab samples were collected on 25th Jan, 19th April and 26th April.

Table 5.2: Results of statistical analysis for samples excluding those containing the blue-

green algae Phormidium. The WWTP was treating for P during April but not during January

sampling.

Mann-Whitney p-values Equivalence test - strength of evidenceGroup Comparison TP TN TN/TP TP TN TN/TP25-Jan-12 u/s vs d/s 0.009 0.047 0.009 Strong Strong Moderate

21-Apr-12 u/s vs d/s 0.14 0.5 0.009 Inconclusive Inconclusive Strong

28-Apr-12 u/s vs d/s 0.016 0.5 0.009 Strong Inconclusive Strong

u/s site 21st vs 28th 0.028 0.5 0.009 Strong Inconclusive Strong

d/s site 21st vs 28th 0.5 0.6 0.6 Inconclusive Inconclusive Inconclusive

Equivalence test assumed +/-10% and a p -values statistically significant if <0.05


2-34129.00

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0

2

4

6

8

10

12

14

16

u/s d/s

Cel

lula

r TN

:TP

ratio

Manawatu River site

25-Jan-2012

21-Apr-2012

28-Apr-2012

Figure 5.1: Ratio of TN:TP in periphyton cells (excluding replicates dominated by

Phormidium) . The error bars show the extreme values (minimum and maximum).


2-34129.00

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Table 5.3: Results of cellular nutrient analysis. The WWTP was treating for P during April

but not during January sampling.

Date us or ds

site /

replicate

TP

(mg/kg)

TN

(mg/kg) TN/TP Dominant periphyton species

25-Jan-12 us us 1a 1830 15600 8.5 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 us us 1b 1690 15500 9.2 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 us us 1c 2100 16900 8.0 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 us us 1d 1210 9900 8.2 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 us us 1f 1340 11700 8.7 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 us us 1e 1500 9600 6.4 Stigeoclonium, Melosira varians, Gomphonema sp., Phormidium

25-Jan-12 ds ds 1a 3400 27000 7.9 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 ds ds 1b 3100 19600 6.3 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 ds ds 1d 3100 13400 4.3 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 ds ds 1e 3900 29000 7.4 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 ds ds 1f 4100 26000 6.3 Stigeoclonium, Melosira varians, Gomphonema sp.

25-Jan-12 ds ds 1c 2800 21000 7.5 Phormidium, Gomphonema sp., Stigeoclonium,

21-Apr-12 us us 2a 4800 38000 7.9 Stigeoclonium, Diatoma cf. tenuis, Gomphonema sp.

21-Apr-12 us us 2b 3200 26000 8.1 Stigeoclonium, Diatoma cf. tenuis, Gomphonema sp.

21-Apr-12 us us 2d 4700 39000 8.3 Stigeoclonium, Diatoma cf. tenuis, Gomphonema sp. (small)

21-Apr-12 us us 2e 4100 32000 7.8 Diatoma cf. tenuis, Stigeoclonium

21-Apr-12 us us 2f 5200 36000 6.9 Stigeoclonium, Diatoma cf. tenuis, Diatoma vulgaris / Gomphonema sp.

21-Apr-12 us us 2c 1560 8000 5.1 Phormidium > Navicula cf. lanceolata > Melosira varians

21-Apr-12 ds ds 1a 4800 31000 6.5 Stigeoclonium, Diatoma vulgaris, Gomphonema sp.

21-Apr-12 ds ds 1b 6100 39000 6.4 Stigeoclonium, Diatoma cf. tenuis/Gomphonema sp.

21-Apr-12 ds ds 1d 4100 23000 5.6

Stigeoclonium, Diatoma cf. tenuis, Gomphonema sp./ Melosira

varians/Navicula cf. lanceolata

21-Apr-12 ds ds 1e 5200 35000 6.7 Stigeoclonium, Diatoma cf. tenuis, Gomphonema sp.

21-Apr-12 ds ds 1f 5300 33000 6.2 Stigeoclonium > Diatoma cf. tenuis, Melosira varians/Diatoma vulgaris

21-Apr-12 ds ds 1c 5100 40000 7.8

Phormidium, Stigeoclonium, Diatoma cf. tenuis, Diatoma vulgaris,

Navicula cf. lanceolata

28-Apr-12 us us 2a 2400 35000 14.6 Diatoma cf. tenuis > Stigeoclonium / Diatoma vulgaris/Gomphonema sp

28-Apr-12 us us 2b 2000 24000 12.0 Diatoma cf. tenuis > Stigeoclonium

28-Apr-12 us us2d 2500 31000 12.4 Diatoma cf. tenuis, Stigeoclonium

28-Apr-12 us us 2e 3700 40000 10.8 Diatoma cf. tenuis, Stigeoclonium, Melosira varians

28-Apr-12 us us 2f 3300 32000 9.7 Diatoma cf. tenuis, Stigeoclonium

28-Apr-12 us us 2c 1540 8500 5.5 Phormidium, > Diatoma cf. tenuis /Gomphonema sp.

28-Apr-12 ds ds 1a 5900 38000 6.4 Diatoma cf. tenuis, Stigeoclonium, Melosira varians

28-Apr-12 ds ds 1b 4500 31000 6.9 Stigeoclonium, Diatoma cf. tenuis ,

28-Apr-12 ds ds 1d 5500 37000 6.7 Diatoma cf. tenuis > Stigeoclonium

28-Apr-12 ds ds 1e 3500 22000 6.3 Diatoma cf. tenuis, Stigeoclonium / Gomphonema sp. / Melosira varians

28-Apr-12 ds ds 1f 3800 23000 6.1

Diatoma cf. tenuis, Stigeoclonium, Gomphonema sp. / Navicula cf.

lanceolata

28-Apr-12 ds ds 1c 4600 40000 8.7 Phormidium, > Diatoma cf. tenuis /Gomphonema sp.

Periphyton taxa listed in order of 'dominant' to those that were 'common abundant'.

Relicates dominated by cyanobacteria are coloured blue and were excluded from our analysis.


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5.3.2 Periphyton bioassays

Comparison of sites

The results of the periphyton bioassays 14th - 27

th April (13 days) and the much shorter

bioassay 29th March – 3

rd April (5 days) are shown in Appendix 5. Both the 5 day bioassay

and the 13 day bioassay showed more periphyton growth at the downstream sites

compared to the upstream site (see Figures 5.2 and 5.3). The difference between sites was

most apparent (and least variable) when looking at the N treatment only; this can be seen

by comparison of p-values from a Mann-Whitney test in Tables 5.4 and 5.5.

Mean chlorophyll a at the combined downstream sites was about 66% higher than

combined upstream sites after the 5 day bioassay, but the absolute biomass at all sites

was very low – indicative of early stages of periphyton colonising the substrates. After the

13 day bioassay there was considerably more periphyton at all sites and about 36% more

chlorophyll a at the downstream sites – pushing the mean chlorophyll a values at site D

above the diatom biomass guideline for maintaining trout habitat (i.e. 200 mg/m2) (Biggs

and Kilroy 2000). This shows that the higher periphyton biomass observed in the river

downstream was caused by factors unrelated to luxury uptake of phosphorus from periods

when the WWTP is not treating for P (although it does not rule out the possibility that luxury

uptake of P also occurs)19

.

During the 13 day bioassay the periphyton biomass was significantly higher at the

downstream sites for the N treatment, P treatment and N+P treatment. This shows that

some factor other than nitrate or phosphate (or N+P) was stimulating periphyton growth

during the period when the WWTP was treating for phosphorus.

During the 5 day bioassay the periphyton biomass was significantly higher at the

downstream sites only for the N treatment. This shows that some factor other than nitrate

was stimulating periphyton growth but it does not rule out the possibility of P limitation

during this initial growth phase.

The 13 day bioassay had about 25% more chlorophyll a at site D compared to site C (see

Figure 5.2). These downstream sites were about 80m apart and the difference between

them might be attributed to difference in faster water velocity at Site D. Table 5.6 shows the

water depth and water velocity above each tray when they were installed and removed.

Initial water velocity was faster at sites A and D (99 cm/s and 94 cm/s respectively

compared to 77 cm/s at sites B and C), but declined as the river receded to be about 44

cm/s at all sites by the end of the experiment. Nutrient uptake rates are enhanced by faster

water velocities that increase the rate of nutrient diffusion to growing cells. Velocities over

about 60 cm/s have been shown to reduce periphyton biomass due to scouring (Horner et al. 1990), but the effects of scouring will be limited during the early stages of growth when

19

Luxury uptake is not supported by comparison of periphyton growth rates at the downstream site in the

river compared to that on the bioassay. The growth rate in the river was 13.4 mg chl a /m2/day over 31 days

between a flood on 24 March and 24th April, the bioassay periphyton had a growth rate of 13.2 mg chl a

/m2/day over 13 day period. Growth was much faster after the first 5 to 10 days. At the upstream site the

periphyton appeared to have a slightly slower growth rate compared to the bioassay (3.9 mg chl a/m2/day

compared to 9.7 mg chl a /m2/day).


2-34129.00

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periphyton biomass is low. Horner et al. (1990) found the positive effect of velocity to be

more evident at low (<0.0075 mg/l) DRP concentrations. C

hl a (

mg/m

2)

u/s d/s c d/s d80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

Figure 5.2: Comparison of periphyton biomass between sites on 27th April (N treatments).

The box shows the median and quartiles, the whiskers show the extreme values.

Chl a (

mg/m

2)

u/s a u/s b d/s c d/s d0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Figure 5.3: Comparison of periphyton biomass between sites on 3rd April (N treatments

only). The box shows the median and quartiles, the whiskers show the extreme values.


2-34129.00

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Table 5.4: Statistical comparison between sites for periphyton bioassay, 27th April 2012

Mann-Whitney, p -valueTreatment us vs

ds (combined)u/s vs d/s c

u/s vs d/s d

d/s c vs d/s d

N 0.002 0.009 0.009 0.11

P 0.007 0.03 0.016 0.75

N+P 0.01 0.075 0.009 0.047

control 0.027 0.25 0.009 0.028

all treatments grouped <0.001 <0.001 <0.001 0.002Equivalence test, +/- 10%N strong strong strong inconclusive

P strong strong strong inconclusive

N+P strong moderate strong moderate

control strong inconclusive strong strong

all treatments grouped strong strong strong strong

Table 5.5: Statistical comparison between sites for periphyton bioassay, 3rd April 2012

Mann-Whitney, p-valueTreatment us vs dsN 0.001P 0.14

N+P 0.3

control 0.9

all treatments grouped 0.05

Equivalence test, +/- 10%N strongP inconclusive

N+P inconclusive

control inconclusive

all treatments grouped inconclusive

Table 5.6: water depth and velocity at each site for the 13 day bioassay.

site Depth (m)Velocity (cm/s) Depth (m)

Velocity (cm/s)

u/s A 42 99.0 25 44.3

u/s B 46 76.7

d/s C 46 76.7 20 44.3

d/s D 41.5 93.9 26 44.3

14th April 27th April


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Comparison between treatments

A comparison of treatments for upstream and downstream sites during the 13 day bioassay

is shown in Figures 5.4 to 5.6. A statistical comparison of the treatments is provided in

Table 5.7. The results show that neither N (nitrate), P nor N+P were limiting periphyton

growth at the upstream site or downstream Site D. There was weak evidence of P limitation

at downstream Site C but the results were not statistically significant and not confirmed by

any corresponding biomass increase on the N+P treatment.

This evidence of P limitation at site C suggests that P could be controlling periphyton

growth in areas of slower velocity once other limiting factors have been removed.

Surprisingly the control treatment was significantly elevated at the downsteam Site D

compared to the N or N+P treatments. The reason for this is not clear; it could be due to

the leaking of nutrients from other treatments interfering with the control treatment in

combination with higher water velocities stimulating algae growth at the downstream side of

the trays used for the experiment. However, visual observation of the trays after they were

removed showed less periphyton on the downstream end of the tray (presumably from

turbulence causing more scouring), which is not consistent with higher biomass on the

control treatments.

There are a number of possible explanations for the 13 day bioassay not showing any

nutrient limitation at the upstream sites. These include upstream periphyton biomass being

controlled by:

The total ammonia concentration rather than nitrate concentration with this control

being released by ammonia in the discharge.

Micronutrients (e.g. molybdenum, cobalt, silica, zinc,) with this control being

released by the micronutrients in the discharge.

Aquatic macroinvertebrate grazers (e.g. mayfly) exerting partial control. Rapid

growth in periphyton at the downstream site could create a positive feedback loop

whereby more periphyton reduces habitat suitability for mayfly, which reduces

grazing pressure.

Some combination of these effects in combination with additional phosphorus due

to the WWTP discharge and DRP entering via groundwater

The N and N+P treatment of the bioassay used sodium nitrate. Some studies have found a

periphyton response to ammonium but not to nitrate. Pan (1993) found algae community

growth was significantly stimulated by either nitrate or ammonia under phosphate enriched

conditions, but the diatoms Gomphonema parvulum and Nitzschia palea strongly preferred

ammonium as an inorganic nitrogen source and showed no significant response to nitrate.

However ammonium limitation is unlikely because cellular nutrient analysis indicated

potential P limitation in periphyton at the upstream site.

Some studies have found periphyton to be limited by micronutrients rather than nitrogen or

phosphorus. Pringle et al. (1986) found that during in situ periphyton bioassays neither N or


2-34129.00

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P were limiting periphyton growth but a micronutrient treatment (Fe, B, Mn, Zn, Co, Mo,

EDTA) supplemented with and without N and P had significantly more chlorophyll a accrual

compared to all other treatments. Figure 5.7 shows the relative composition of algae

compared to the relative concentration of dissolved nutrients in the river (normalised

relative to phosphorus). Of the variables we measured only nitrogen and zinc were close to

being limiting relative to phosphorus (both we elevated below the discharge). It is also

possible that limitation occurred from a micronutrient that we didn‟t test i.e. silica (which

might control diatom growth), cobalt, and molybdenum.

A number studies have shown periphyton communities to be controlled grazing by aquatic

macroinvertebrates (e.g. Pan 1993). Welch et al. (1992) found lower than expected

periphyton biomass associated with high macroinvertebrate grazer density, riparian

shading and unsuitable substrate. Grazing by macroinvertebrates has been found to

remove 11-29 mg chl a /m2/day (Walton 1990 in Welch et al. 1992) and 37 mg chl a

/m2/day (Jacoby 1987 in Welch et al. 1992). This is higher than the measured periphyton

growth rate at the downstream site in the river (22 mg chl a /m2/day over 19 day period of

5th to 24

th April) and on the bioassay (13.2 mg chl a /m

2/day over the 13 day period).

The actual rate of grazing will depend on grazer density, type and temperature. The

macroinvertebrate survey found that on 20th April (six days into the bioassay and the day

before cellular nutrients were collected) the grazer density20

at sites 1000m u/s and 800m

d/s was 246/m2 and 532/m

2 respectively. By 27

th April (the day bioassays were removed),

the grazer density had increased to 486/m2 (range 170-740) at the upstream site, but had

reduced to 116/m2 (range 30-250) at the 800m downstream site. Thus, during the second

week of the bioassay grazers at the downstream site reduced in density to well below

densities needed to control periphyton biomass. The decline is likely to have been caused

by excess periphyton biomass reducing the suitability of the habitat for mayfly.

The main grazer was Deleatidium mayfly. The densities of Deleatidium at the upstream site

were typical of rivers in the National River Water Quality Network (NRWQN). The NRWQN

site on the Manawatu River at Teaches College had a median Deleatidium density of 161

/m2 – suggesting that the April low flow period had higher densities compared to long term

sampling at Teaches College (John Quinn pers. Comm. 2012). We speculate that the

macroinvertebrate grazers may exert partial control of periphyton accrual rates but are not

expected to prevent dense periphyton development because grazing rates are expected to

be less than growth rates.

There is no data to suggest that mayfly or caddisfly density was reduced by any toxic

effects. No variable was found in the effluent in sufficient concentrations to cause chronic

toxicity to macroinvertebrates after mixing. Whole effluent toxicity tests were undertaken in

2000 as part of the consent application. Waste water samples were tested for freshwater

algae (using 72 hour cell growth), microtox (using 15 minute light output) and 48 hour

survival of Cladocera (D. magna). The results indicated a 5.5 fold dilution of the wastewater

was required for no toxicity (evidence by D. Cameron, 2003) – which occurs after a very

short distance.

20

Grazers were defined as mayflys + Aoteapsyche caddisfly, + Elmid beetle lavae + snails.


2-34129.00

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Chl a (

mg/m

2)

N P N+P control80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

Figure 5.4: Comparison of treatments at the upstream Site A, 27th April 2012. The box

shows the median and quartiles, the whiskers show the extreme values.

Chl a (

mg/m

2)

N P N+P control80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

Figure 5.5: Comparison of treatments at downstream Site C, 27th April 2012. The box



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Chl a (

mg/m

2)

N P N+P control80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

Figure 5.6: Comparison of treatments at downstream Site D, 27th April 2012. The box


A comparison of treatments for grouped upstream and downstream sites during the 5 day

bioassay is shown in Figures 5.7 and 5.8. A statistical comparison of the treatments is

provided in Table 5.9. Consistent with the 13 day bioassay there is no indication of nitrogen

elevating periphyton growth at either the upstream or downstream sites. However there

was evidence that either P or N+P was elevating periphyton growth at the upstream sites

but not at the downstream sites. This indication of possible P limitation is not conclusive

because the control treatment is also elevated above N treatment but this could be due to

interference between the treatments.

The difference between the 5 day bioassay and the 13 day bioassay may be due to

different water quality conditions during the experiments (e.g. there was higher nitrate and

total ammonia concentrations during the 5 day bioassay compared to the 13 day bioassay).

Alternatively it could be due to different requirements at different stages of growth and as

the periphyton mat becomes thicker. A third option is that if the periphyton is limited by

grazing by aquatic macroinvertebrates. Grazer density takes some time to build after a

flood event so it is possible that the 5 day bioassay reflects a situation where the density of

macroinvertebrate grazers (mostly mayflies) is too low to control periphyton biomass and

the 13 day bioassay reflects a situation where grazer density has increased sufficiently to

be a primary control on periphyton biomass at the upstream site.

Grazing by aquatic macroinvertebrates might also explain the higher periphyton biomass

found at some of the control treatments, because more turbulence at the downstream end

of trays (near the control treatments) might reduce grazer abundance in this section of the

trays.


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Table 5.7: Mann-Whitney statistical comparison of treatments on each bioassay, 27th April

2012

siteTreatment u/s a d/s c d/s d d/s

combinedN vs control ns ns 0.047 0.2

N+P vs control ns ns 0.016 0.17

P vs control ns 0.17 0.12 ns

N vs P ns 0.03 ns 0.04N vs N+P ns ns ns ns

N+P vs P ns 0.03 ns 0.028ns = not statistically significant (and p -value >0.2)

Cells in bold = statistically significant (p -value <0.05)

Table 5.8: Relative elemental composition of algae (normalised on total dissolved P on a

molar basis) compared to the relative concentration of dissolved constituents of river water

on 18th and 26

th April 2012. Bold values are similar to algal requirements (adapted from

Hecky and Kilham 1988)

mg/l mols

Element River u/s River u/s River u/s Algal

N 0.1445 0.0103 39.9 11.1

Si 96

K 1.65 0.0422 163 1.3

P 0.008 0.00026 1.0 1

Na 14 0.6090 2357 0.74

Mg 3.3 0.1357 525.5 0.66

Ca 24.5 0.6113 2366 0.63

S 3.45 0.1076 416 0.54

Fe 0.095 0.0017 6.6 0.32

Zn 0.00095 0.000015 0.056 0.012

B 0.022 0.0020 7.9 0.008

Cu 0.000405 0.000006 0.025 0.004

Mn 0.00525 0.00010 0.370 0.003

Co 0.003

Mo 0.00002

Composition relative to P


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Chl a (

mg/m

2)

N PN+P

cont

rol

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Figure 5.7: Comparison of treatments at the upstream Sites A & B on 3rd April 2012. The

box shows the median and quartiles, the whiskers show the extreme values.

Chl a (

mg/m

2)

N P N+P control0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Figure 5.8: Comparison of treatments at downstream Sites C and D, 3rd April 2012. The

box shows the median and quartiles, the whiskers show the extreme values.


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Table 5.8: Mann-Whitney statistical comparison of treatments on each bioassay, 3rd April

2012

siteTreatment u/s a us b d/s c d/s d u/s

combinedd/s

combinedN vs control 0.008 0.1 ns ns 0.001 ns

N+P vs control ns ns ns 0.01 ns 0.12

P vs control 0.08 ns ns 0.14 0.2 ns

N vs P ns 0.05 ns ns 0.007 ns

N vs N+P 0.01 ns ns 0.07 ns

N+P vs P ns 0.11 ns 0.13 ns ns

ns = not statistically significant (and p -value >0.2)

Cells in bold = statistically significant (p -value <0.05)

5.4 Summary

Cellular nutrient analysis

Analysis of cellular nutrients identified that an optimal TN:TP ratio for the periphyton

community (excluding cyanobacteria) was about 6.3.

Cellular nutrient analysis showed potential phosphorus limitation of periphyton

growth at the upstream site but not at the downstream site even after two weeks of

the WWTP treating for P. This was indicated by:

o An elevated ratio of TN:TP at the upstream site;

o An increase in the TN:TP ratio at the upstream site during the week of

periphyton growth with no change at the downstream site;

o No significant difference in the TN:TP ratio during a period when the WWTP

wasn‟t treating for P (25 January) and a period when it was (during April).

Cellular nutrient analysis and bioassays assess potential nutrient limitation at a

particular point in time and do not rule out the possibility of nitrogen becoming

limiting under different circumstances.

Periphyton nutrient bioassay

Periphyton biomass was statistically significantly higher at the downstream site

compared to the upstream site.

The higher periphyton biomass downstream is caused by factors that occur while

the WWTP is treating for P and is thus unrelated to periphyton using P stored from

any previous luxury uptake of P from before treatment started.


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During the 13 day bioassay some factor other than concentrations of nitrate and/or

phosphorus was primarily limiting periphyton growth upstream and stimulating

periphyton growth downstream. This was indicated by two lines of evidence:

o The treatments of N, P and N+P all showing a statistically significant

increase in periphyton biomass between the upstream and downstream

sites.

o There was no statistically significant difference between any of the

treatments at any site.

During the 13 day bioassay there was weak evidence (not statistically significant) of

P limitation at downstream Site C. This suggests that P might be controlling

periphyton grow in areas of slower velocity once other limiting factors have been

removed.

During the 5 day bioassay there was some evidence of P limiting periphyton growth

at the upstream sites but not at the downstream sites. The result was not definitive

due to the control treatment also having high biomass but was nevertheless

indicated by:

o Significantly higher periphyton biomass at the downstream sites for the N

treatment but not for the treatments of P or N+P.

o The upstream sites having significantly more periphyton biomass on the P

and N+P treatments compared to the N treatment.

P appears to be a secondary limiting factor on periphyton growth but something

other than N or P is the primary limiting factor. There are several possible factors

that could account for downstream stimulation of periphyton growth other than

nitrate or phosphorus. These include:

o Stimulation of growth by micronutrients (e.g. silica, cobalt, molybdenum,

zinc, soluble sugars) in the discharge and possibly groundwater sources.

o Dissolved carbon from the discharge promoting heterotrophic growths which

in turn enhance periphyton colonisation, nutrient availability and a growth.

o Stimulation of growth by total ammonia in the discharge – but not by nitrate

which was used in the bioassay. This is unlikely because cellular nutrient

analysis indicated potential P limitation in periphyton at the upstream site.

o Rapid growth in periphyton at the downstream site creating a positive

feedback loop whereby more periphyton reduces habitat suitability for

mayfly, which reduces grazing pressure.

o Some combination of these effects in combination with additional

phosphorus due to the WWTP discharge and DRP entering via

groundwater.


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The results of bioassays and cellular nutrient analysis do not rule out the possibility

of nitrogen limitation of green algae (Stigeoclonium sp.) at the upstream site late in

the succession.


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6 Aquatic macroinvertebrates and periphyton cover

6.1 Aim

Aquatic macroinvertebrate sampling was undertaken to clarify the extent to which the

PNCC WWTP discharge was affecting periphyton growth and the aquatic

macroinvertebrate community in the Manawatu River. Sampling occurred on two sequential

occasions during a period of low flow when the WWTP was treating for phosphorus to

distinguish the potential impact of the WWTP discharge before and after treating for P.

6.2 Method

6.2.1 Macroinvertebrates

A macroinvertebrate assessment was undertaken on two occasions over a receding flow, a

third sample was planned but a flood event prevented this being practical. Samples were

undertaken on:

20th April 2012, 28 days since the last flood >3x median flow (on 23

rd March) and

after 8 days of the WWTP treating for P;

27th April 2012, 35 days since the last flood >3x median flow and after 15 days of

the WWTP treating for P

Samples were collected from five sites in the Manawatu River:

1000m above the discharge point;

800m above the discharge point;

800m below the discharge point;

1000m below the discharge point;

Upstream of Longburn STP discharge (about 1.4km downstream of Mangaone

Stream confluence).

Sampling locations are shown on Figure 6.1.

The site upstream of Longburn STP was added to see if any change was evident further

downstream.

The macroinvertebrate sampling followed Protocols C3 (Hard-bottomed quantitative) from

the Ministry for the Environment‟s “protocols for sampling macroinvertebrates in wadeable

streams” (Stark et al. 2001). This involved collecting 5 replicate 0.1 m2 Surber samples

approximately located near separate transects used for the periphyton assessment of

cover (at least 5 metres apart).

The following measurements were recorded for each Surber sample:


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Velocity (head rod);

Depth

Periphyton cover and type as per periphyton assessment above,

Making precise measurements for each replicate sample was intended to help confirm the

link between the macroinvertebrate indices and periphyton cover.

Samples were sent to Stark Environmental to be identified and counted using Protocol P3

(full count) of Stark et al. (2001). Macroinvertebrate taxa was identified to the taxonomic

resolution level specified for use of the Macroinvertebrate Community Index (MCI).

The following ecological indices were used to assess the biological health of the river and

the effects of the discharge on the stream ecology:

Taxa Richness: This is a measure of the types of invertebrate taxa present in each

sample. Generally in streams, the greater the numbers of taxa present, the higher the

quality of the environment.

EPT richness and % EPT abundance (Ephemeroptera-Plecoptera-Trichoptera). This

measures the number of pollution sensitive mayfly, stonefly and caddisfly (EPT) taxa in a

sample excluding the tolerant Oxyethira and Paroxyethira. A high EPT number is indicative

of good water and habitat quality.

Macroinvertebrate Community Index (MCI). The MCI is an index for assessing the water

quality and „health‟ of a stream using the presence/absence of benthic macroinvertebrates

(Stark 1985).

Quantitative MCI (QMCI). The Quantitative MCI is similar to the MCI but utilises

quantitative data. The QMCI is based on the relative sensitivity of different taxa in a sample

to changes in water quality. The QMCI is designed to be particularly sensitive to changes in

the relative abundance of individual taxa within a community (Stark 1993, Stark 1998).

The MCI and QMCI reflect the sensitivity of the macroinvertebrate community to pollution,

with higher scores indicating higher water quality. Generally accepted water quality classes

for different MCI and QMCI scores and soft-bottomed version are shown in Table 6.1.

Table 6.1: Quality thresholds for interpretation of the MCI & QMCI.

Quality Class Stark (1998) descriptions MCI QMCI

Excellent Clean water > 120 > 6.0

Good Doubtful quality or possible mild pollution 100 – 120 5.0 - 6.0

Fair Probable moderate pollution 80 – 100 4.0 – 5.0

Poor Probable severe pollution < 80 < 4.0


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Figure 6.1: Location of aquatic macroinvertebrate sampling.

6.2.2 Periphyton cover

Visual periphyton measures were made at the same time as aquatic macroinvertebrate

sample collections, using the same method as described above for „periphyton dynamics‟.

Assessments were made within each of the replicates defined by the Surber sampler to

improve comparability of the results.

6.2.3 Statistics

Tests for equivalence and inequivalence were based on +/- 20% change compared to the

upstream control sites. A 20% change corresponds to water quality target in the One Plan

that “Discharges to water to cause no more than a 20 % reduction in QMCI score between appropriately matched habitats upstream and downstream of discharges to water.” Allowing up to a 20% change recognises that habitats can seldom be perfectly matched

and even small changes in substrate size, flow and location can impact on

macroinvertebrate composition to some extent.


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6.3 Results

6.3.1 Aquatic macroinvertebrates

The summary results of aquatic macroinvertebrate sampling are shown in Table 6.2 and

the full table of results for 20th and 27

th April are in Appendix 2. MCI scores (graphed in

Figure 6.2) indicate that water quality in the Manawatu River is on the boarder of categories

„fair‟ to „good‟. Only one site (800m upstream on 20th April) had an MCI score that complied

with the target set in the Proposed One Plan (POP) of exceeding 100. A week later on 27th

April there had been a reduction in MCI scores at two sites (800m u/s and 100m d/s) and

no site had an MCI score exceeding 100.

Statistical differences were analysed by grouping the two upstream sites (1000m u/s and

800m u/s) and the first two downstream sites (800m d/s and 1000m d/s). A summary of the

results of a non-parametric Mann-Whitney test is shown in Table 6.3 and results of an

equivalence test (with a practically important difference set at +/- 20%) is shown in Table

6.4. A Mann-Whitney test found no statistical difference in MCI scores between upstream

and downstream on either sample dates, and it found no statistical difference in MCI scores

between sample dates for either upstream or downstream sites. The results of the

equivalence test were inconclusive.

QMCI scores (graphed in Figure 6.3) and % EPT abundance21

(Figure 6.4) were a more

responsive indicator of the effects of the discharge. On both sample dates there were

statistically significant lower QMCI scores at downstream site compared to upstream sites,

this difference was stronger on the second sample date (on 27th April and after 15 days of

the WWTP treating for P). The equivalence test found „moderate evidence‟ of a >20%

difference in QMCI between upstream and downstream on 20th April and „strong evidence‟

on 27th April.

Comparing the change in QMCI scores in the week between sample dates found no

statistically significant difference in QMCI at the upstream sites, but strong evidence of a

decline in QMCI during the week at the downstream sites. The equivalence test showed

strong evidence of a decline in QMCI during the week up to a practical difference of +/-

29%.

Interestingly, the site above Longburn (below Mangaone Stream) had similar QMCI scores

between sample dates suggesting that the site was less sensitive to any impact of the

WWTP discharge during this period. This may be due to the WWTP discharge (and other

possible inputs) not being fully mixed until 1400m downstream of the discharge point.

The abundance and composition of macroinvertebrate taxa groups is summarised in Figure

6.5 and Figure 6.6 for sampling on 20th April and 27

th April respectively. This shows that on

20th April there was similar abundance of mayfly and EPT taxa at the two downstream and

upstream sites (statistical analysis were inconclusive due to the large variation). There

were also more Diptera (predominantly Orthocladiinae) at the downstream sites and this is

what drove the decline in QMCI and %EPT taxa between the upstream and downstream

21

There was negligible difference between % EPT abundance and % EPT abundance (excluding

Hydroptilidae taxa).


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sites. One week later, on 27th April, the abundance mayfly (and to a lesser extent true fly)

had increased at the upstream sites (probably reflecting a continued recovery from the

large flood on 23rd

March); however at the two sites immediately downstream there was an

increase in true fly abundance and a substantial decline in mayfly abundance (a 2 way

ANOVA on normalised mayfly data found the difference to be statistically significant).

Table 6.2: Median results of five replicate Surber samples at sites in the Manawatu River

upstream and downstream of the WWTP (20th April 2012 and 27th April 2012).

site Date

Number

of taxa

No

individuals MCI QMCI

%EPT

richness

%EPT

abundance

EPT

abundance

Mayfly

(No./m2)

1000m u/s 20-Apr 5 30 92 6.4 40.0 78.9 30.0 230

800m u/s 20-Apr 5 28 116 6.8 60.0 96.3 28 230

800m d/s 20-Apr 8 109 90 4.4 50.0 45.0 109 300

1000m d/s 20-Apr 5 50 100 6.1 33.3 62.5 50 280

d/s Mangaone 20-Apr 8 41 93 4.0 50.0 36.6 41 70

1000m u/s 27-Apr 6 75 90 6.5 40.0 73.9 75 350

800m u/s 27-Apr 7 63 93 6.7 55.6 84.2 63 500

800m d/s 27-Apr 8 76 91 2.9 44.4 13.6 76 60

1000m d/s 27-Apr 5 28 80 2.6 20.0 7.1 28 10

d/s Mangaone 27-Apr 6 50 93 3.8 50.0 38.7 50 100

EPT abundacne excludes Hydroptilidae and is the sum of the 5 replicates.


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40

50

60

70

80

90

100

110

120

130

140

1000m u/s 800m u/s 800m d/s 1000m d/s d/sMangaone

MC

I sco

re20th April. 8 daysof P treatment

27th April. 15 daysof P treatment

Figure 6.2: Median MCI scores in the Manawatu River upstream and downstream of the

WWTP during a low flow period. Error bars show the full range of five replicate samples.

The red line indicates the Proposed One Plan target of this section of the Manawatu River.

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0


QM

CI s

core



Figure 6.3: Median QMCI scores in the Manawatu River upstream and downstream of the

WWTP during a low flow period. Error bars show the full range of five replicate samples.

The red line indicates the boundary between “good” and “fair” water quality.


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0

10

20

30

40

50

60

70

80

90

100


% E

PT a

bund

ance



Figure 6.4: Median % EPT abundance in the Manawatu River upstream and downstream

of the WWTP during a low flow period. Error bars show the full range of five replicate

samples.


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0

50

100

150

200

250

300

350

400

450

500


Abun

danc

e

Platyhelminthes

Dobsonflies

Snails

Oligochaeta

Beetles

True Flies

Stoneflies

Caddisflies

Mayflies

Figure 6.5: Macroinvertebrate composition in the Manawatu River upstream and

downstream of the WWTP during a low flow period on 20th April 2012. Double these

abundances to express as number per m2.


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0

50

100

150

200

250

300

350

400

450

500


Abun

danc

e

Platyhelminthes

Dobsonflies

Snails

Oligochaeta

Beetles

True Flies

Stoneflies

Caddisflies

Mayflies

Figure 6.6: Macroinvertebrate composition in the Manawatu River upstream and

downstream of the WWTP during a low flow period on 27th April 2012. Double these

abundances to express as number per m2.

Table 6.3: Summary p-values of Mann-Whitney test between upstream (and downstream

sites (grouped excluding Longburn site) and between dates. The p-value were adjusted for

multiple comparisons and considered statistically significant if <0.05.

Indexu/s vs d/s 20th April

u/s vs d/s 27th April

20th vs 27th at u/s sites

20th vs 27th at d/s sites

Number of taxa 0.08 0.90 0.25 0.97

Number individuals 0.16 0.31 0.15 * 0.60

MCI 0.16 0.14 0.25 0.42

QMCI 0.01 <0.001 0.71 0.002%EPT richness 0.05 0.14 0.25 0.51

%EPT abundance 0.002 <0.001 0.25 0.002EPT abundance 0.160 0.260 0.15 * 0.5

* shows results where p -value = 0.05 before adjusting for multiple comparisons.


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Table 6.4: Summary results of an equivalence test between upstream and downstream

sites (grouped) and between dates. The equivalence test used a significance level of p-

value <0.05 and a practically important difference set at +/- 20%.





Number of taxa Inconclusive Inconclusive Inconclusive Inconclusive

Number individuals Inconclusive Inconclusive Inconclusive Inconclusive

MCI Inconclusive Inconclusive Inconclusive Inconclusive

QMCIModerate

evidence

Strong

evidence

No practical

difference

Strong

evidence

%EPT richnessModerate

evidence

Moderate

evidenceInconclusive Inconclusive

%EPT abundanceStrong

evidence

Strong

evidence

No practical

difference

Strong

evidence

EPT abundance Inconclusive Inconclusive Inconclusive Inconclusive

'Moderate' = moderate evidence of a >20% difference.

'Strong' = strong evidence of a >20% difference.

6.3.2 Periphyton cover

The periphyton cover within areas sampled for macroinvertebrates is summarised in Table

6.5 and statistical comparisons are shown in Table 6.6. The cover of thick diatoms (>3mm

thick) and long filamentous algae was higher at the downstream sites and exceeded the

guidelines set for protection of aquatic habitat (i.e. upper level of 30% cover by long

filamentous algae and 60% cover of thick diatom mats or cyanobacteria (Biggs 2000).

There was statistically significantly more cover of “slimy” green filamentous algae at the

downstream sites on both sample occasions (Figure 6.7). The variation in periphyton cover

between replicates was reduced when that cover data was aggregated into the Periphyton

Slimyness Index (PSI) which weights different thickness categories (see Figure 6.8).

The upstream sites showed no significant difference in periphyton cover during the week

between the two sample occasions. However, the downstream sites (800m and 1000m d/s)

had significantly more periphyton cover. These patterns are generally consistent with the

results of QMCI scores from macroinvertebrate monitoring.

There was a strong negative relationship between periphyton cover (as measured by PPI)

and QMCI scores, i.e. more periphyton was associated with lower QMCI scores. Figure 6.8

shows that the relationship became stronger on 27th April and upstream and downstream

sites became more distinct groups (all downstream sites, for both dates, are included within

the grey line on the graph). On 20th April the r

2 was 0.46 and on 27

th April the r

2 was 0.64.

22

22

The equation describing the relationship on 20th April was: QMCI = -0.035 PPI + 6.784. And on 27

th April

was: QMCI = -1.356 ln(PPI) + 9.3434.


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The mayfly (Deleatidium sp.) was the most common macroinvertebrate grazer found on the

in the river. This species showed a different pattern with periphyton growth compared to the

QMCI. The biomass of mayfly increased with PPI up to a PSI value of about 40-50% – after

which it declined again.

Between the sampling dates of 20th April and 27

th April the site 800m downstream had a

substantial decline in QMCI scores (4.4 to 2.9) and mayfly abundance (300/m2 to 60/m

2).

This corresponded to an increase in periphyton cover from a PPI of 55% to 80% and an

increase in periphyton biomass from about 300 mg/m2 to 450 mg/m

2 (estimated from

Figure 4.8). If it is assumed that the decline in mayfly abundance was caused by the

increasing periphyton biomass then the frequency of this event occurring could be

estimated using the same method as used for periphyton in Section 4. It took about 29

days for the site 800m downstream to exceed a biomass of 300 mg/m2 (Figure 4.5), which

corresponded to about 1.24 times per summer.

Table 6.5: Median periphyton cover and hydrology over the areas sampled for

macroinvertebrates.

site Date

Depth

(cm)

Velocity

(cm/s)

Mats

<3mm

Mats

>3mm

Slimy green

algae >2cm

Coarse green

algae >2cm PPI PSI

1000m u/s 20-Apr 22 77 90 0 10 0 10 26

800m u/s 20-Apr 20 83 90 0 5 0 10 24

800m d/s 20-Apr 24 63 45 0 50 0 55 52

1000m d/s 20-Apr 15 70 70 10 20 0 30 34

d/s Mangaone 20-Apr 25 77 30 20 30 10 70 52

1000m u/s 27-Apr 28 54 90 0 10 0 10 26

800m u/s 27-Apr 26 70 85 0 10 0 15 29

800m d/s 27-Apr 28 77 20 20 60 0 80 60

1000m d/s 27-Apr 25 99 40 10 50 0 60 52

d/s Mangaone 27-Apr 21 63 10 5 70 0 90 70

PPI = Periphyton Proliferation Index = percent cover of long filaments + thick mats

PSI = Periphyton Slimyness Index = cover of weighted thickness category


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Table 6.6: Summary p-values of statistical test between upstream (and downstream sites

(grouped excluding Longburn site) and between dates. The p-value were adjusted for

multiple comparisons and considered statistically significant if <0.05





Depth (m) ns ns ns 0.08

Velocity (cm/s) ns 0.022 0.07 0.18

Slimy filamentous >2cm 0.004 <0.001 ns 0.05PPI 0.002 <0.001 ns 0.007PSI 0.002 <0.001 ns 0.007ns = not significant

Equivalence test - strength of evidence





Depth (m) Inconclusive Inconclusive Inconclusive Moderate

Velocity (cm/s) Inconclusive Moderate Inconclusive Inconclusive

Slimy filamentous >2cm Strong Strong Inconclusive Moderate

PPI Strong Strong Inconclusive Strong

PSI Strong Strong Inconclusive Moderate

Equivalence test assume +/- 20% difference and p -values significant if <0.05

0

10

20

30

40

50

60

70

80

90

100


Perip

hyto

n Pr

olife

ratio

n In

dex

(%) 20th April. 8 days

of P treatment


Figure 6.7: Median periphyton proliferation index in the Manawatu River upstream and

downstream of the WWTP during a low flow period. Error bars show the full range of five

replicate samples.


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0

10

20

30

40

50

60

70

80

90


Perip

hyto

n Sl

imyn

ess

Inde

x20th April. 8 daysof P treatment


Figure 6.8: Median Periphyton Slimyness Index for sites in the Manawatu River upstream

and downstream of the WWTP during a low flow period. Error bars show the full range of

five replicate samples.


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Figure 6.8: Relationship between the QMCI and the Periphyton Slimyness Index for sites

in the Manawatu River upstream and downstream of the WWTP. Downstream sites are

incorporated within the grey circle.

6.3.3 Summary of macroinvertebrate survey

Aquatic macroinvertebrates were sampled upstream and downstream of the WWTP

discharge on 20th April, 8 days after the WWTP starting treatment for P and on 27

th

April, 15 days after the WWTP starting treatment.

There was no statistically significant change in MCI scores between upstream and

downstream of the discharge and between sample occasions.

QMCI and % EPT taxa were a sensitive indicator of changes in aquatic

macroinvertebrate community downstream of the discharge and over time. On both

sample dates there were statistically significant lower QMCI scores at downstream

site compared to upstream sites.

In the week between sample dates QMCI scores did not significantly change at the

upstream sites, but there was strong evidence that QMCI scores at the two

downstream sites reduced by about 29% during the week.

On the 20th of April there was a greater abundance of mayfly and EPT at the two

immediately downstream sites. A week later on 27th April the number of EPT taxa

had increased at the upstream site but decreased at the two downstream sites

(although none of these changes were statistically significant). The number of

diptera had increased at all sites except downstream of Mangaone Stream.


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The decline in QMCI scores observed downstream of the WWTP on 27th April

discharge did not persist down the river to the site downstream of Mangaone Stm

(upstream of Longburn).

There was a strong negative correlation between periphyton cover and QMCI.

Periphyton cover showed similar patterns to the QMCI, i.e. more cover at all the

downstream sites and an increase between the two sample occasions between

sites 800m downstream and 100m downstream (but not at the other sites).

The decline in mayfly abundance observed on the 27th April represents a significant

change in community structure. This degree of impact was predicted to occur 1.24

times per summer for the site 800m downstream (based on 29 days to exceed a

biomass of 300 mg/m2).


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7 Synthesis and Conclusions

This report has described the results of a joint work programme for monitoring the

Manawatu River from November 2011 to May 2012. The key purposes of this monitoring

were to address:

The effects that are occurring in the periphyton and aquatic macroinvertebrate

communities downstream of the WWTP; including identifying the extent to which the

WWTP discharge is affecting periphyton growth and the aquatic macroinvertebrate

community in the Manawatu River.

The causes of these effects; including other sources of nutrients in the vicinity of the

WWTP, and which (if any) nutrient is controlling periphyton growth.


lessen adverse effects on the river environment, including refining the timing and

extent of phosphorus removal from the wastewater in order to limit downstream

periphyton growth.

This section synthesises the result of monitoring to address each of these questions.

7.1 Effects of the WWTP discharge on periphyton growth and aquatic macroinvertebrate communities.

The WWTP and other contaminants entering the river in the vicinity of the WWTP caused a noticeable increase in periphyton growth and a decline in the quality of the aquatic macroinvertebrate community during periods of extended low flow.

The adverse effects on biota only became evident during periods of low flow. This is typical of river dynamics because periphyton biomass is strongly influenced by the period of time since the last flood that removed periphyton biomass. In practice this meant that periphyton cover and biomass remained low (i.e. <30 mg/m

2 and PPI

<10%) when Manawatu River flows were above about 50 m3/s.

During low flow periods the periphyton at sites downstream of the WWTP grew faster than at upstream sites and exceeded guideline trigger values sooner. The periphyton biomass exceeded filamentous periphyton guidelines for trout habitat (120 mg/m

2) after about 37 days, 17 days and 19 days of growth for sites upstream,

800m downstream and 1400m downstream respectively. This corresponded to respective exceedence frequencies of 1.1 times per summer, 1.9 times per summer and 1.7 times per summer.

The site 800m downstream of the WWTP showed faster periphyton growth compared to the site 1400m downstream, probably because the effluent was not fully mixed until after 1000 - 1200m downstream and concentrations of nutrients and were higher.

The periphyton community was usually dominated by diatom species and the green algae Stigeoclonium sp. There was more cyanobacteria cover at the site 800m


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downstream but only small amounts (3% cover) and this effect didn‟t persist far downstream.

The increase in periphyton biomass was associated with a decline in the quality of the macroinvertebrate community (as measured by QMCI scores) at the downstream sites during periods of low flow.

At the downstream sites periphyton continued to accumulate and aquatic macroinvertebrates continued to decline even during a period when the WWTP was treating for P. A reduction in the abundance of mayfly (300/m

2 to 60/m

2) at the

800m downsteam site corresponded with an increase in periphyton cover and biomass (from about 300 mg/m

2 to 450 mg/m

2). Using a 21 year flow record it was

estimated that on average this degree of change might occur 1.24 times per summer.

The macroinvertebrate community at the site upstream of Longburn (about 1.4 km downstream of Mangaone Stream confluence) had lower QMCI and %EPT abundance than at the upstream of WWTP sites but did not change over time.

7.2 What is causing the effects observed in the Manawatu River downstream of the WWTP plant

An increase in periphyton biomass and cover was, at least partially, driving a decline in the quality of the macroinvertebrate community (e.g. QMCI) both spatially (downstream of the WWTP) and temporally as periphyton biomass accumulated during periods of low flow. A decline in the density of macroinvertebrate grazers will create a positive feedback allowing periphyton biomass to increase even further.

During low flow in April, when the WWTP was alum dosing for phosphorus (P), the discharge was estimated to increase bioavailable phosphorus (DRP) by 7% to 23% (ca. 0.0005 to 0.0016 g/m

3) above background concentrations at site 800m d/s.

However, measured concentrations of DRP in the river were about 160% (ca. 0.011 g/m

3) above background concentrations (and about 2.4 times higher than what

might be attributed to the WWTP). This indicates another external (e.g. groundwater) or internal (e.g. desorption of dissolved P from river sediments) source of P to the river during periods of low flow.

The additional source of DRP means that the full effects of the WWTP removing phosphorus (P) from the discharge were not often being realised in the river.

There was evidence of groundwater seepage to the river about 400m to 600m downstream of the discharge. The precise location of groundwater inputs may change with river level.

Despite the influence of other DRP sources, when the WWTP was removing P from the effluent, the DRP concentrations in the river water downstream were still reduced to low levels (i.e. a low flow mean of 0.008 g/m

3) which should have been

sufficient to limit the rate of periphyton growth. The higher than expected periphyton growth at the 800m downstream site might be explained by periphyton experiencing higher DRP concentrations at the sediment surface than measured in the water as DRP enters the river from groundwater seepage and/or desorption from sediments.


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During low flows periphyton biomass in the Manawatu River upstream of the WWTP discharge was limited by something other than the macronutrients, nitrate nitrogen or phosphorus. This was indicated by:

- The nutrient bioassay which supplied excess phosphorus for periphyton growth at the upstream site but still had lower biomass accrual than the downstream site.

- Comparison of measured periphyton biomass in April with predictions from a regression model (Biggs 2000) which found measured periphyton biomass was lower than those predicted under a range of scenarios.

Nevertheless, phosphorus did appear to be a secondary limiting factor for periphyton growth upstream of the WWTP. This was indicated by increasing cellular ratios of TN:TP during a growth period and compared to the downstream site.

While the evidence pointed to possible P limitation (in combination with something else), we cannot rule out the possibility of duel limitation of N and P also occurring. For example, during low flow periods soluble inorganic nitrogen (SIN) was at times within concentrations that might reduce the periphyton growth rate.

Whatever was limiting periphyton growth upstream was not limiting it downstream. Downstream of the WWTP neither N or P were limiting periphyton growth, allowing periphyton on the bioassays to quickly attain high biomass and coverage (about 66% more than upstream). There was weak evidence of phosphorus limitation in areas of slower water, but biomass was still about 33% higher than the upstream site).

At this stage we can only speculate as to what is the primary control on periphyton biomass (and hence the primary cause of d/s periphyton growth). Possible causes include:

- Micronutrients (e.g. silica, cobalt, molybdenum, zinc) controlling periphyton growth upstream, and the discharge providing these nutrients.

- Grazing by macroinvertebrates (e.g. mayflies) partially controlling periphyton biomass upstream. While at the downstream sites periphyton growth rates exceed removal rates by grazers.

In addition to this, it appears that the river substrate (gravels and cobbles) at the site 800m downstream are being „conditioned‟ by heterotrophic biofilms which might reduce the period of time after a flood for the early stages of periphyton growth, allowing more rapid growth sooner. This was indicated by:

- Comparative growth rates between sites during April; and

- Comparison of measured periphyton biomass in April with predictions from a regression model which found higher periphyton biomass in the river than those predicted even when unrealistically high DRP concentrations were assumed.

- The presence of fungus filaments in some of the periphyton samples.


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One possible explanation for higher initial growth rates downstream is that dissolved organic carbon from the discharge (part of the BOD load) stimulates heterotrophic biofilms, which conditions the substrate for periphyton to more quickly colonize. Heterotrophic biofilms might also increase the rate of nutrient cycling within the periphyton community.

7.3 Potential management actions

Removing phosphorus (P) from the effluent during periods of low flow is reducing DRP concentrations. It is important to continue treating for P during low flow periods because this is providing some control on periphyton growth. Furthermore, discharging more P could cause a change in the type of periphyton e.g. a relative increase in green filamentous algae.

Further reducing the concentration of P in the discharge during periods of low flow (when treatment is currently occurring) is unlikely to provide significant benefit to the river because there appears to be another source of P entering during low flow periods.

One possible management action is to start removing P from the effluent at flows higher than half median flow. This should be seriously considered if dissolved phosphorus is being released from river sediments during periods of low flow when the discharge is being treated for P. If this mechanism is not occurring to any great extent, then treating earlier would not stop the more rapid periphyton growth at the downstream sites, although it still might slow the initial phases of periphyton development at the site 800m downstream (but apparently not at the site 1400m downstream).

Sometimes a period of low flow is interrupted with small rain events sufficient to raise the river above 40 m

3/s but not sufficient to remove periphyton cover. In these situations

(where periphyton is already present) the extent of periphyton biomass at the downstream sites might be reduced by continuing P treatment until periphyton cover/biomass is reduced (e.g. to <30 mg/m

2 or PPI <10%) – this might be approximated using a flow statistic.

This study has answered a number of questions regarding why there is more periphyton downstream of the WWTP discharge. There are factors controlling the rate of periphyton growth at the upstream site as well as factors stimulating periphyton growth at the downstream site that cannot be simply explained by phosphorus and nitrate nitrogen in the discharge. The results provide some clear pointers for further investigations that would help unravel the dynamics of periphyton growth in the Manawatu River near Palmerston North and refine the most appropriate management actions to reduce effects of the discharge. These investigations should include:

i. Investigate the possibility of river sediments desorbing DRP to river water during periods when the WWTP is treating for P by testing the sorption capacity of river sediments. If river sediments are found to sorb and desorb dissolved P than a management response might be to start treating for P sooner. If not then it becomes more important to identify sources of dissolved P to groundwater.

ii. Investigate whether heterotrophic biofilms stimulate periphyton growth and/or enhance P release at the site 800m downstream? If this is that case than reducing the amount of BOD in the discharge might reduce periphyton growth rates in the river prior to full mixing.


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iii. Investigate whether micronutrients or total ammonia is controlling/stimulating periphyton growth in the Manawatu River. This could involve repeating a periphyton nutrient bioassay to include treatments with micronutrients (e.g. silica, cobalt, molybdenum, zinc, soluble sugars). Nitrogen should be in the form of ammonium.

iv. Investigate the sources of contaminants to groundwater seeping to the river during periods of low flow. Potential source of DRP might include ponds from the sewage treatment plant or possibly the landfill. Some work is already being done by Horizons RC that might further clarify the possible sources and magnitude of this contamination.

v. Investigate the extent to which macroinvertebrate grazers are controlling periphyton growth at the upstream and downstream sites. This could be done by undertaking a grazer exclusion experiment.


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References

Ardón, M.; Pringle, C.M 2007. The quality of organic matter mediates the response of

heterotrophic biofilms to phosphorus enrichment of the water column and substratum.

Freshwater Biology 52: 1762-1772.

Biggs, B.J.F 2000. NZ Periphyton Guideline: Detecting, Monitoring and Managing Enrichment of Streams, Prepared for the Ministry for the Environment.

Biggs, B.J.F. 2000 b Eutrophication of streams and rivers: dissolved nutrient-chlorophyll

relationships for benthic algae. Journal of the North American Benthological Society 19

(1):17-31

Biggs, B.J.F., Kelly D.J. 2002. The relationship between dissolved nutrients and periphyton

biomass in the Manawatu River downstream of the Palmerston North City Council

domestic waste discharge. Prepared for horizons MW . NIWA Client Report:

CHC02/08.

Biggs, B.J.F., Kilroy, K.C. 2000. Stream periphyton monitoring manual. Ministry for the

Environment, Wellington.

Earthtech Consulting 1995. Supplementary groundwater investigations. Awapuni landfill, Palmerston North City Council. Prepared by A.H. Nelson and P.I. Kelsey March 1995.

Pringle, C.M.; Paaby-Hansen, P.; Vaux P.D.; Goldman, C.R. 1986. In situ nutrient assays

of periphyton growth in a lowland Costa Rican stream. Hydrobiologia 134: 207-213.

Cameron D. 2002. Statement of evidence of David James Cameron. In the matter of the

applications of the Palmerston North City Council for resource consents for its

wastewater scheme.

Cameron, D. 2011. A benthic biota survey of the Manawatu River at Palmerston North.

Prepared by MWH for Palmerston North City Council. February 2011.

Clausen B, Biggs BJF. 1997. Relationships between benthic biota and hydrological indices

in New Zealand streams. Freshwater Biology 38: 327 - 342.

Collier, K., Kelly, J. Champion, P. 2007. Regional guidelines for ecological assessments of freshwater environments: Aquatic plant cover in wadeable streams. Environment

Waikato Technical Report 2006/47.

Haggard B.E., Stoner R.J. 2009. Long-term changes in sediment phosphorus below a rural

effluent discharge. Hydrology and Earth System Sciences Discussions 6: 767-789.

Harding J, Clapcott J, Quinn J, Hayes J, Joy M, Storey R, Greig H, Hay J, James T, Beech

M, Ozane R, Meredith A Boothroyd I 2009. Stream habitat assessment protocols for wadable rivers and streams of New Zealand. University of Canterbury.

Frances and Death R. 2001. Nuisance periphyton growth in the Manawatu River – responses to nutrient enrichment.


2-34129.00

13/09/2012 89

Hill, W.R., Fanta, S. 2008. Phosphorus and light co-limit periphyton growth at subsaturating

irradiances. Freshwater Biology 53: 215-225.

Horner, R.R., Welch, E.B., Seeley, M.R., Jacoby J.J. 1990. Responses of periphyton to

changes in current velocity, suspended sediment and phosphorus concentration.

Freshwater Biology 24: 215-232.

Hecky, R.E., Kilham P. 1988. Nutrient limitation of phytoplankton in freshwater and marine

environments: A review of recent evidence of the effects of enrichment. Limnology and Oceanography 1988: 796-822

Kilroy, C, Biggs, B., Death, R. (2008). A periphyton monitoring plan for the Manawatu-Wanganui Region. NIWA client report: CHC2008-03.

Lucci, G.M., McDowell R.W., Condron L.M. 2010. Evaluation of base solutions to determine

equilibrium phosphorus concentrations (EPC0) in stream sediments. International Agrophysics 24: 157-163

McArthur, K.J., Roygard R., Clark M. 2010. Understanding variations in the limiting nitrogen

and phosphorus status of rivers in the Manawatu-Wanganui Region, New Zealand.

Journal of Hydrology 49 (1): 15-33.

McConchie, J. 2009. Periphyton accrual times – Manawatu River. Memo prepared by Opus

International Consultants.

Ministry for the Environment and Ministry of Health 2009. New Zealand guidelines for cyanobacteria in recreational freshwaters – interim guidelines. Prepared for the

Ministry for the Environment and Ministry of Health by SA Wood, DP Hamilton, WJ

Paul, KA Safi and WM Williamson. Wellington:MfE.

Palmer-Felgate E.J., Mortimer RJK, Krom M.D., Jarvie H.P. 2010. Impact of point-source

pollution on phosphorus and nitrogen recycling in stream-bed sediments.

Environmental Science and Technology 44: 908-914.

Pan, Y. 1993. The effects of nutrients on periphyton. Thesis. Bowling Green State

University.

Pringle CM, Paaby-Hansen, P; Vaux PD; Goldman, CR 1986. In situ nutrient assays of

periphyton growth in a lowland Coasta Rican Stream. Hydrobiologia 134: 207213.

Rutherford, J.C., Ovenden R., Nagels J.W. 1997. Low flow mixing measurements in the Manawatu River. NIWA Consultancy Report PNC60201/3. Prepared for Palmerston

North City Council.

Stark, J. D. 1985: A macroinvertebrate community index of water quality for stony streams,

water and soil miscellaneous publication 87.

Stark, J.D. 1998. SQMCI: A biotic index for freshwater macroinvertebrate coded

abundance data. New Zealand Journal of Marine and Freshwater Research 32: 55-66.


2-34129.00

13/09/2012 90

Stark, JD; Boothroyd, IKG; Harding JS; Maxted, JR; Scarsbrook, MR 2001. Protocols for sampling macroinvertebrates in wadeable streams. New Zealand Macroinvertebrate

Working Group Report no. 1. Prepared for the Ministry for the Environment.

Sustainable Management Fund Project No. 5103. 57p.

Stark JD, Maxted JR 2007. A user guide for the Macroinvertebrate Community Index.

Prepared for the Ministry for the Environment. Cawthron Report No.1166. 58 p.

Turner, BL, Baxter, R, Whitton BA 2003. Nitrogen and phosphorus in soil solutions and

drainage streams in Upper Teesdale, northern England: implications of organic

compounds for biological nutrient limitation. Science of The Total Environment, Vol 314-316: 153-170

Welch, E.B., Quinn, J.M., Hickey, W. 1992. Periphyton biomass related to point-source

nutrient enrichment in seven New Zealand streams. Water Resources 26 (5): 669-675.

Wood SA, Heath M, Ryan KG 2010. Fine scale spatial variability of anatoxin-a and

homoanatoxin-a production in benthic cyanobacteria; implication for monitoring and

management. Journal of Applied Microbial Ecology 109: 2011–2018.

Wood SA, Young R 2011. Benthic Cyanobacteria and Toxin Production in the Manawatu -Wanganui Region. Prepared for Horizons Regional Council. Cawthron Report No.

1959. 36 p. plus appendices


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Appendix 1: Photographs of samples sites

1 Manawatu River upstream PNCC STP 18-April-2012 2 Manawatu River upstream PNCC STP 24-April-2012

3 Manawatu River upstream PNCC STP 3-May-2012 4 Manawatu River upstream PNCC STP 09-May-2012

5 Manawatu River 800m downstream PNCC STP18-April-2012


7 Manawatu River 800m downstream PNCC STP3-May-2012







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Appendix 2: Result of aquatic macroinvertebrate sampling in Manawatu River, 20th April 2012 and 27th April 2012

Manawatu River replicate 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

site MCI

1000m

u/s

1000m

u/s

1000m

u/s

1000m

u/s

1000m

u/s

800m

u/s

800m

u/s

800m

u/s

800m

u/s

800m

u/s

800m

d/s

800m

d/s

800m

d/s

800m

d/s

800m

d/s

1000m

d/s

1000m

d/s

1000m

d/s

1000m

d/s

1000m

d/s

d/s

Mangaone

d/s

Mangaone

d/s

Mangaone

d/s

Mangaone

d/s

Mangaone

PO28819. Protocols C3, P3, QC3. TV 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr 20-Apr

Mayflies

Austroclima sp. 9 - - - - - - - - 1 - - - - - - - - - - - - - - - -

Deleatidium sp. 8 18 27 13 33 23 23 26 11 20 57 6 66 113 13 30 5 34 3 88 28 42 7 3 9 7

Stoneflies

Acroperla trivacuata 5 - - - - - - - - - - - - - - - - - - - 1 - - - - -

Zelandobius furcillatus group 5 - - - - - - - - - - - - - - - - - - - - - 1 - - -

Zelandoperla decorata 10 - - - - - - - - - - - - - - - - - - - - - - 1 - -

Dobsonflies

Beetles

Elmidae 6 1 - - 1 - - 2 - 1 - - - 2 - 3 1 - - - 1 8 - - 1 1

True Flies

Aphrophila neozelandica 5 - - - - - - - - - - 1 - - - - - - - - - 1 - - - -

Austrosimulium spp. 3 - - - 1 - - 1 - - - - - 1 - 1 - - - - - 2 - - - 2

Eriopterini 9 - - - - - - - - - - - 1 - - - - - - - - - - - - -

Orthocladiinae 2 2 2 4 6 4 - - - 4 3 17 25 18 12 52 2 13 6 20 16 17 30 18 17 12

Tanytarsus spp. 3 2 - - - 2 - 1 - - 6 4 12 9 6 11 - 3 2 9 3 24 11 7 8 1

Caddisflies

Aoteapsyche spp. 4 6 - - - 1 - 76 3 2 23 1 13 5 3 9 - - - 3 - 30 15 10 4 10

Costachorema xanthopterum 7 - - - - - - - - - - - - - - - - - - - - - 1 - - -

Hydrobiosis copis 5 - - - - - 1 - - - - - - - - - - - - - - - 1 - 2 -

Hydrobiosis frater 5 - - - - - - - - - - 1 1 - - - - - - - - - - - - -

Hydrobiosis spp. 5 - - - - - - 2 - - 1 - - - - - - - - - - - - - - -

Hydrobiosis umbripennis 5 - - 1 - - - - - - - 1 - - - 2 - - - - - - - - - 1

Olinga spp. 9 - - - - - - - - - - - - - - 1 - - - - - - - - - -

Psilochorema leptoharpax 8 - 1 1 - - - 1 1 - 1 - - - 1 - - - 2 - 1 - - - - 1

Pycnocentria evecta 7 - - - - - - - - - - - - 1 - - - - - - - - - - - -

Pycnocentrodes sp. 5 - - - - - - - - - - - - - 1 - - - - - - - - - - -

Oligochaeta 1 - - - 6 2 - - - - 1 - 5 5 4 - - - - 3 - 2 2 - - -

Platyhelminthes 3 - - - - - - - - - - - - - - - - - - 1 - - - - - -

Snails

Potamopyrgus antipodarum 4 - - - - - - - - - - - 1 1 - - - - 1 1 - 2 3 - - -

Number of taxa 5 3 4 5 5 2 7 3 5 7 7 8 9 7 8 3 3 5 7 6 9 9 5 6 8

Number of individuals 29 30 19 47 32 24 109 15 28 92 31 124 155 40 109 8 50 14 125 50 128 71 39 41 35

MCI 92 120 115 80 72 130 106 133 116 89 90 90 84 89 100 107 87 100 71 107 80 87 108 93 98

QMCI 6.3 7.6 6.6 6.2 6.4 7.9 5.0 7.2 6.8 6.4 3.6 5.6 6.6 4.4 4.2 6.3 6.1 4.4 6.3 5.7 4.9 3.4 3.4 4.0 4.2

EPT abundance (excl Hydroptilidae) 29 30 19 47 32 24 109 15 28 92 31 124 155 40 109 8 50 14 125 50 128 71 39 41 35

%EPT richness (excl. Hydroptilidae) 40.0 66.7 75.0 20.0 40.0 100.0 57.1 100.0 60.0 57.1 57.1 37.5 33.3 57.1 50.0 33.3 33.3 40.0 28.6 50.0 22.2 55.6 60.0 50.0 50.0

%EPT abundance 82.8 93.3 78.9 70.2 75.0 100.0 96.3 100.0 82.1 89.1 29.0 64.5 76.8 45.0 38.5 62.5 68.0 35.7 72.8 60.0 56.3 35.2 35.9 36.6 54.3

%EPT abundance (excl. Hydroptilidae) 82.8 93.3 78.9 70.2 75.0 100.0 96.3 100.0 82.1 89.1 29.0 64.5 76.8 45.0 38.5 62.5 68.0 35.7 72.8 60.0 56.3 35.2 35.9 36.6 54.3


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Manawatu River replicate 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

site MCI

1000m

u/s

1000m

u/s

1000m

u/s

1000m

u/s

1000m

u/s

800m

u/s

800m

u/s

800m

u/s

800m

u/s

800m

u/s

800m

d/s

800m

d/s

800m

d/s

800m

d/s

800m

d/s

1000m

d/s

1000m

d/s

1000m

d/s

1000m

d/s

1000m

d/s

d/s

Mangaone

d/s

Mangaone

d/s

Mangaone

d/s

Mangaone

d/s

Mangaone

PO29010. Protocols C3, P3, QC3. TV 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr 27-Apr

Mayflies

Coloburiscus humeralis 9 - - - 1 - - 1 - - - - - - - - - - - - - - - - - -

Deleatidium sp. 8 57 35 17 64 30 30 95 50 45 52 18 1 6 16 1 3 - 1 - 51 10 4 6 16 10

Stoneflies

Zelandobius furcillatus group 5 - - - - - - - - - 1 - - - - - - - - - - - - - - -

Beetles

Elmidae 6 - 1 1 1 - - 1 - 2 3 2 1 - 4 1 1 - - 1 1 1 - - - -

True Flies

Aphrophila neozelandica 5 - - - - - - - - - - 1 - - - - - - - - - - - - - -

Austrosimulium spp. 3 - - - 2 - - 1 - - - - - - - - - - - - - - - - - -

Eriopterini 9 - - - - - - - - - - - - - 1 - - - - - - - - 1 - -

Orthocladiinae 2 7 23 5 12 3 - 10 9 7 13 56 37 45 34 15 17 3 21 9 60 25 6 17 21 31

Polypedilum spp. 3 - - - - - - - - - - - - - - - - - - 1 - - 1 - - -

Tanytarsus spp. 3 - 4 - 3 2 3 3 - 2 2 23 10 17 16 2 3 1 8 2 7 3 4 1 6 7

Caddisflies

Aoteapsyche spp. 4 16 11 - 5 2 2 35 4 4 21 5 5 1 3 1 - - - 1 10 10 1 4 16 2

Costachorema spp. 7 - - - - - - - - - - - - - 1 - - - - - - - - - 1 -

Hydrobiosis copis 5 - - - - - - - - - - 1 - 1 - - - - - - - - - - - -

Hydrobiosis frater 5 - - - - - - - - 1 - - - - - - - - - - - - - - - -

Hydrobiosis spp. 5 - - - - - - 1 - - - 1 - 1 - - - - - - - - - 2 - -

Hydrobiosis umbripennis 5 - - - - - - - - - - - - 1 - - - - - - - 2 - - - -

Oxyethira albiceps 2 - - - - - - - - 1 - - - - - - - - - - 1 - - - - -

Psilochorema leptoharpax 8 - - - - 1 - 1 - 1 - - - - 1 1 - - - - 1 - - - - -

Pycnocentrodes sp. 5 - - - 1 - - - - - - - - - - - - - - - - - - - - -

Oligochaeta 1 - - - 1 8 2 - - - 1 2 - 4 - 1 4 - - - - - 2 - - -

Snails

Physa sp. 3 - - - - - - - - - - - - - - - - - - - 2 - - - - -

Potamopyrgus antipodarum 4 - 1 - 4 - 1 - - - - - - 1 - - - - - - 4 - - - 1 -

Number of taxa 3 6 3 10 6 5 9 3 8 7 9 5 9 8 7 5 2 3 5 9 6 6 6 6 4

Number of individuals 80 75 23 94 46 38 148 63 63 93 109 54 77 76 22 28 4 30 14 137 51 18 31 61 50

MCI 93 90 107 90 87 80 107 93 95 83 85 92 77 118 91 80 50 87 72 89 93 70 103 93 85

QMCI 6.7 5.2 6.6 6.5 6.0 6.9 6.5 6.9 6.7 6.0 3.4 2.6 2.8 4.0 2.9 2.8 2.3 2.5 2.6 4.6 3.8 3.6 3.9 4.3 3.4

EPT abundance (excl Hydroptilidae) 80 75 23 94 46 38 148 63 62 93 109 54 77 76 22 28 4 30 14 136 51 18 31 61 50

%EPT richness (excl. Hydroptilidae) 66.7 33.3 33.3 40.0 50.0 40.0 55.6 66.7 50.0 42.9 44.4 40.0 55.6 50.0 42.9 20.0 0.0 33.3 20.0 33.3 50.0 33.3 50.0 50.0 50.0

%EPT abundance 91.3 61.3 73.9 75.5 71.7 84.2 89.9 85.7 82.5 79.6 22.9 11.1 13.0 27.6 13.6 10.7 0.0 3.3 7.1 46.0 43.1 27.8 38.7 54.1 24.0

%EPT abundance (excl. Hydroptilidae) 91.3 61.3 73.9 75.5 71.7 84.2 89.9 85.7 81.0 79.6 22.9 11.1 13.0 27.6 13.6 10.7 0.0 3.3 7.1 45.3 43.1 27.8 38.7 54.1 24.0


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Appendix 3: Results of synoptic survey 19th April and 26th April 2012.

Synoptic Survey field + lab results v3.xlsx

Date Site Distance (m) Time Temperature DO %

DO

(mg/l)

Field EC

(uS/cm)

Lab EC

(mS/m)

Field

pH Lab pH

CBOD5

(mg/l)

COD

(mg/l)

NH4-N

(mg/l)

Nitrate-N

(mg/l)

Nitrite-N

(mg/l)

NNN

(mg/l)

SIN

(mg/l)

Total N

(mg/l)19/04/2012 Manawatu @ U/S PNCC STP -1200 1705 14.5 110.6 11.51 212.4 21.5 8.12 8.1 1.3 <30 0.016 0.22 <0.002 0.22 0.236 0.3519/04/2012 Turitea @ U/S Manawatu Confluence -1100 1325 13.6 90.6 9.59 194.9 19.9 7.62 7.6 1 <30 0.031 0.066 0.0023 0.068 0.099 0.1719/04/2012 Manawatu @ 600m U/S PN STP -600 1645 14.6 109.8 11.13 212.3 21.6 8.18 8.2 1.2 <30 0.012 0.22 <0.002 0.22 0.232 0.3419/04/2012 PNCC STP @ Tertiary Treated Effleunt 81 7.2 9.5 65 35 0.006 0.0027 0.0087 35.0087 4019/04/2012 PNCC STP @ Post Wetland Discharge 80.8 7.3 4.8 58 35 0.044 0.06 0.1 35.1 4019/04/2012 Manawatu @ 100m D/S PN STP 100 1600 14.7 110.2 11.39 247.1 7.8919/04/2012 Manawatu @ 200m D/S PN STP 200 1605 14.6 108.3 11.22 229.6 23.3 7.99 8 1.4 <30 1.1 0.24 0.0092 0.25 1.35 1.519/04/2012 Manawatu @ 300m D/S PN STP 300 1540 14.6 111.1 11.51 226 8.0419/04/2012 Manawatu @ 400m D/S PN STP 400 1536 14.6 111 11.53 223.2 22.6 8.08 8.1 1.2 <30 0.77 0.23 0.0062 0.23 1 119/04/2012 Manawatu @ 500m D/S PN STP 500 1620 14.5 112.8 11.72 220.8 8.0619/04/2012 Manawatu @ Awapuni Shingle Plant (600m d/s STP) 600 1445 14.4 113.2 11.71 221.2 22.4 8.04 8.1 1.5 <30 0.67 0.24 0.0076 0.24 0.91 0.8619/04/2012 Manawatu @ 700m D/S PN STP 700 1455 14.4 113 11.79 221.4 8.0319/04/2012 Manawatu @ D/S PNCC STP 800 1430 14.3 114.3 11.93 221.1 22.3 8.02 8.1 1.4 <30 0.64 0.23 0.0097 0.24 0.88 0.8919/04/2012 Kahuterawa U/S Manawatu Confluence 820 1105 14.3 107.4 11.15 90.8 9.3 7.53 7.6 1.1 <30 0.016 0.02 <0.002 0.02 0.036 0.09319/04/2012 Manawatu @ 1400 D/S PNCC STP 1400 1240 14.1 114 11.91 215.5 21.9 8.03 8.1 1.4 <30 0.26 0.23 0.011 0.24 0.5 0.6319/04/2012 Manawatu @ 1800m D/S PN STP 1800 1226 14.1 113.7 11.9 215.3 21.8 7.95 8.1 1.2 <30 0.25 0.23 0.013 0.24 0.49 0.6119/04/2012 Mangaone @ Awapuni Racecourse 1006 13.4 77.9 8.3 334.1 33.8 7.09 7.4 0.97 <30 0.056 0.51 0.0046 0.51 0.566 0.7619/04/2012 Mangaone @ U/S Manawatu Confluence 2250 931 13.4 79.6 8.47 345.6 34.9 7.1 7.3 1.2 <30 0.75 0.6 0.023 0.62 1.37 1.519/04/2012 Manawatu @ 150m D/S Mangaone Confluence 2400 1115 14 112.9 11.87 214.9 21.8 7.88 8.1 1.3 <30 0.23 0.23 0.013 0.25 0.48 0.5826/04/2012 Manawatu @ u/s PNCC STP -1200 1421 14.5 125.3 12.74 218.4 22.4 8.74 8.6 1.3 36 0.016 0.037 <0.002 0.037 0.053 0.1726/04/2012 Turitea @ u/s Manawatu Confluence -1100 1150 12.3 83.7 8.98 196.1 20.2 7.37 7.5 0.72 <30 0.028 0.068 <0.002 0.068 0.096 0.1726/04/2012 Manawatu @ 600m u/s PNCC STP -600 1415 14.7 122.8 12.44 218 22.3 8.78 8.7 1.3 <30 0.017 0.034 <0.002 0.034 0.051 0.1526/04/2012 PNCC STP @ Tertiary Treated Effleunt 81.3 7 15 75 35 0.017 <0.002 0.017 35.017 4026/04/2012 PNCC STP @ Post Wetland Discharge 81.7 7.1 13 60 35 0.016 0.01 0.026 35.026 3926/04/2012 Manawatu @ 100m d/s PN STP 100 1350 14.7 114.8 11.53 253.4 8.3726/04/2012 Manawatu @ 200m d/s PN STP 200 1355 14.5 117.5 11.96 239.9 24.4 8.38 8.3 1.4 <30 1.3 0.087 0.0093 0.097 1.397 1.426/04/2012 Manawatu @ 300m d/s PN STP 300 1340 14.4 117.2 11.94 235.1 8.4926/04/2012 Manawatu @ 400m d/s PN STP 400 1335 14.4 121.6 12.42 230.9 23.6 8.51 8.4 1.3 <30 0.76 0.053 0.0041 0.057 0.817 0.726/04/2012 Manawatu @ 500m d/s PN STP 500 1324 14.2 118.7 12.2 227.7 8.4926/04/2012 Manawatu @ Awapuni Shingle Plant (600m d/s STP) 600 1315 14.1 120.7 12.45 227.4 23.2 8.47 8.4 1.2 <30 0.53 0.061 0.0042 0.065 0.595 0.8126/04/2012 Manawatu @ 700m d/s PN STP 700 1315 14 121.7 12.58 227.4 8.4426/04/2012 Manawatu @ d/s PNCC STP 800 1250 13.9 119.8 12.39 226.2 23.2 8.33 8.3 1.3 <30 0.51 0.071 0.0048 0.076 0.586 0.6826/04/2012 Kahuterawa @ u/s Manawatu Confluence 820 1105 13 96.4 10.2 93.2 9.6 7.65 7.5 0.52 <30 0.033 0.05 <0.002 0.05 0.083 0.09426/04/2012 Manawatu @ 1400m d/s PNCC STP 1400 1044 13.1 116.1 12.25 220.2 22.5 8.38 8.3 1.2 <30 0.17 0.081 0.005 0.086 0.256 0.3526/04/2012 Manawatu @ 1800m d/s PN STP 1800 1026 13 117.1 12.39 220.3 22.5 8.23 8.2 1.1 <30 0.16 0.085 0.005 0.09 0.25 0.3626/04/2012 Mangaone @ Awapuni Racecourse 935 12.5 64.3 6.83 346.7 35.5 7.06 7.3 0.76 <30 0.063 0.53 0.0055 0.54 0.603 0.7126/04/2012 Mangaone @ U/S Manawatu confluence 2250 800 12.5 59.8 6.42 353.3 35.9 6.82 7.2 1.1 <30 0.63 0.67 0.024 0.7 1.33 1.526/04/2012 Manawatu @ 150m d/s Mangone Confluence 2400 1006 12.8 111.3 11.86 220.9 22.5 7.96 8.2 1.3 <30 0.14 0.095 0.0056 0.1 0.24 0.34

ANZECC guideline 0.9


Date Site Distance (m)19/04/2012 Manawatu @ U/S PNCC STP -120019/04/2012 Turitea @ U/S Manawatu Confluence -110019/04/2012 Manawatu @ 600m U/S PN STP -60019/04/2012 PNCC STP @ Tertiary Treated Effleunt19/04/2012 PNCC STP @ Post Wetland Discharge19/04/2012 Manawatu @ 100m D/S PN STP 10019/04/2012 Manawatu @ 200m D/S PN STP 20019/04/2012 Manawatu @ 300m D/S PN STP 30019/04/2012 Manawatu @ 400m D/S PN STP 40019/04/2012 Manawatu @ 500m D/S PN STP 50019/04/2012 Manawatu @ Awapuni Shingle Plant (600m d/s STP) 60019/04/2012 Manawatu @ 700m D/S PN STP 70019/04/2012 Manawatu @ D/S PNCC STP 80019/04/2012 Kahuterawa U/S Manawatu Confluence 82019/04/2012 Manawatu @ 1400 D/S PNCC STP 140019/04/2012 Manawatu @ 1800m D/S PN STP 180019/04/2012 Mangaone @ Awapuni Racecourse19/04/2012 Mangaone @ U/S Manawatu Confluence 225019/04/2012 Manawatu @ 150m D/S Mangaone Confluence 240026/04/2012 Manawatu @ u/s PNCC STP -120026/04/2012 Turitea @ u/s Manawatu Confluence -110026/04/2012 Manawatu @ 600m u/s PNCC STP -60026/04/2012 PNCC STP @ Tertiary Treated Effleunt26/04/2012 PNCC STP @ Post Wetland Discharge26/04/2012 Manawatu @ 100m d/s PN STP 10026/04/2012 Manawatu @ 200m d/s PN STP 20026/04/2012 Manawatu @ 300m d/s PN STP 30026/04/2012 Manawatu @ 400m d/s PN STP 40026/04/2012 Manawatu @ 500m d/s PN STP 50026/04/2012 Manawatu @ Awapuni Shingle Plant (600m d/s STP) 60026/04/2012 Manawatu @ 700m d/s PN STP 70026/04/2012 Manawatu @ d/s PNCC STP 80026/04/2012 Kahuterawa @ u/s Manawatu Confluence 82026/04/2012 Manawatu @ 1400m d/s PNCC STP 140026/04/2012 Manawatu @ 1800m d/s PN STP 180026/04/2012 Mangaone @ Awapuni Racecourse26/04/2012 Mangaone @ U/S Manawatu confluence 225026/04/2012 Manawatu @ 150m d/s Mangone Confluence 2400

ANZECC guideline

DRP

(mg/l)

Total

Dissolved P

(mg/l)

Organic P

(mg/l)

Total P

(mg/l)

E. coli

(MPN/100ml)

Total Coliforms

(MPN/100ml)

Total

Hardness

(as CaCO3)

Total

Alkalinity

(as CaCO3)

Bicarbonate

Alkalinity

(as HCO3)

Calcium

(Total)

Calcium

Hardness

(CaCO3)

(Total)

Magnesium

Hardness

(as CaCO3)

(Total)

Carbonate

Alkalinity

(as CO3)0.007 0.01 0.001 0.011 39 260 70 72 88 23 56 14 <10.041 0.039 0.007 0.046 1700 4000 47 54 65 12 30 17 <10.007 0.007 0.004 0.011 71 650 72 74 90 23 58 14 <10.032 0.99 0.31 1.3 18 2000 62 180 220 18 44 18 <10.04 0.096 1.104 1.2 770 13000 64 180 220 18 45 18 <1

0.026 0.034 0.017 0.051 88 1000 71 76 93 23 57 14 <1

0.021 0.018 0.012 0.03 100 730 71 76 93 23 57 14 <1

0.018 0.02 0.008 0.028 83 820 73 76 92 23 59 15 <1

0.018 0.019 0.006 0.025 64 440 72 74 90 23 57 14 <10.006 0.008 0.001 0.009 110 1200 16 18 21 3.7 9.1 7.1 <10.012 0.016 0.005 0.021 75 440 71 74 91 23 57 14 <10.012 0.012 0.007 0.019 73 920 70 75 91 23 57 14 <10.019 0.02 0.08 0.1 1200 5600 90 81 99 22 54 36 <1.00.021 0.028 0.092 0.12 440 2400 93 90 110 23 57 35 <1.00.011 0.015 0.001 0.016 74 550 71 72 87 23 57 14 <1.0

<0.005 0.006 0.005 0.011 31 390 ND 79 96 26 ND ND <1.00.03 0.034 0.01 0.044 1300 2300 49 55 67 13 32 17 <1.0

<0.005 0.006 0.005 0.011 44 460 ND 79 65 26 ND ND 160.009 0.11 0.81 0.92 27 730 67 170 210 19 49 18 <1.00.019 0.08 0.76 0.84 340 23000 68 170 210 20 50 19 <1.0

0.022 0.017 0.022 0.039 75 730 ND 82 100 26 ND ND <1.0

0.023 0.015 0.015 0.03 77 920 ND 81 99 26 ND ND <1.0

0.012 0.013 0.013 0.026 48 770 80 81 99 26 65 15 <1.0

0.011 0.015 0.01 0.025 83 650 ND 80 97 26 ND ND <1.00.007 0.008 0.002 0.01 140 2000 18 19 24 4.1 10 7.5 <1.00.006 0.009 0.005 0.014 77 820 79 78 96 26 65 15 <1.00.006 0.008 0.005 0.013 93 820 79 79 97 26 64 15 <1.00.018 0.024 0.069 0.093 580 4200 100 88 110 25 62 39 <1.00.022 0.031 0.061 0.092 210 2400 100 95 120 26 65 38 <1.00.006 0.009 0.004 0.013 76 730 81 79 97 27 66 15 <1.0



ANZECC guideline

Aluminium

Dissolved

(mg/l)

Aluminium

Total (mg/l)

Arsenic

Dissolved

(mg/l)

Chromium

Dissolved

(mg/l)

Chromium

Total

(mg/l)

Copper

Dissolved

(mg/l)

Iron

Dissolved

(mg/l)

Iron

Total

(mg/l)

Lead

Dissolved

(mg/l)

Magnesium

Total (mg/l)

Manganese

Dissolved

(mg/l)

Manganese

Total (mg/l)

Nickel

Dissolved

(mg/l)

Potassium

Total

(mg/l)0.093 0.056 0.00036 0.000048 0.00036 0.00057 0.11 0.14 0.000081 3.3 0.0095 0.0068 0.00039 1.7

0.0068 0.037 0.00029 0.000067 0.00027 0.00057 0.35 0.52 0.000054 4.1 0.046 0.046 0.00025 2.10.016 0.06 0.00036 0.00023 0.00025 0.00045 0.06 0.15 0.000051 3.4 0.007 0.0067 0.00038 1.70.16 3.3 0.00031 0.00039 0.00054 0.00091 0.057 0.1 0.00034 4.3 0.042 0.04 0.0022 140.6 3 0.00029 0.00039 0.00055 0.0014 0.061 0.14 0.00035 4.4 0.042 0.042 0.0021 14

0.014 0.16 0.00036 0.000041 0.00043 0.00048 0.059 0.16 <0.00005 3.4 0.006 0.0082 0.00033 2.1

0.056 0.11 0.00033 0.000036 0.00032 0.00044 0.063 0.14 <0.00005 3.3 0.0056 0.007 <0.0002 1.9

0.043 0.11 0.00038 0.00022 0.00041 0.00047 0.076 0.15 0.000052 3.6 0.006 0.0073 0.0003 2

0.085 0.11 0.00041 0.00026 0.00026 0.00053 0.13 0.15 0.000082 3.4 0.0068 0.0067 0.00031 1.90.0089 0.019 0.00013 0.00021 0.00035 0.00049 0.047 0.075 <0.00005 1.7 0.0058 0.0063 <0.0002 1.10.029 0.082 0.00038 0.000098 0.00031 0.00048 0.08 0.14 <0.00005 3.4 0.0057 0.0067 0.00029 1.80.028 0.08 0.00038 0.0002 0.00027 0.00046 0.079 0.14 <0.00005 3.3 0.0058 0.0067 0.00029 1.80.024 0.089 0.00068 0.00031 0.00028 0.00086 0.78 1.2 0.00035 8.6 0.082 0.084 0.00059 4

0.0024 0.071 0.00043 0.00023 0.00031 0.00062 0.46 1.3 0.00011 8.6 0.084 0.086 0.0006 4.20.025 0.068 0.00037 0.00014 0.00033 0.00044 0.077 0.14 <0.00005 3.4 0.0058 0.0065 0.00029 1.8

0.0056 0.024 0.00031 0.00025 0.000014 0.00024 0.08 0.09 <0.00005 ND 0.0052 0.0037 <0.0002 1.60.025 0.13 0.00027 0.00028 0.00013 0.00036 0.47 0.56 0.000072 4.2 0.047 0.037 0.00022 2

0.0051 0.033 0.0003 0.00029 0.000026 0.00024 0.069 0.092 <0.00005 ND 0.0052 0.0039 <0.0002 1.60.55 3.3 0.00019 0.00047 0.00024 0.00036 0.077 0.11 0.00026 4.4 0.043 0.043 0.0019 140.59 2.6 0.0002 0.00046 0.00027 0.00042 0.084 0.13 0.00024 4.5 0.044 0.044 0.0018 14

0.053 0.16 0.00032 0.00026 0.000051 0.00027 0.076 0.1 0.000071 ND 0.0079 0.0046 0.00029 2.1

0.037 0.12 0.00028 0.0003 0.000042 0.00023 0.072 0.1 0.000073 ND 0.006 0.0045 0.00025 1.9

0.045 0.08 0.0003 0.00027 0.000029 0.00021 0.079 0.09 <0.00005 3.6 0.0058 0.0033 0.00023 1.8

0.042 0.076 0.00029 0.00026 0.000028 0.00024 0.082 0.086 <0.00005 ND 0.0057 0.0029 0.00022 1.80.0093 0.022 0.000076 0.00026 <0.00001 0.00037 0.063 0.054 0.000094 1.8 0.0089 0.008 <0.0002 1.10.018 0.049 0.00028 0.0003 <0.00001 0.00019 0.068 0.087 <0.00005 3.6 0.0059 0.0035 0.00021 1.70.018 0.049 0.00027 0.00025 <0.00001 0.00019 0.072 0.085 <0.00005 3.6 0.0061 0.0037 0.00022 1.7

0.0063 0.075 0.00044 0.00027 0.000057 0.00045 0.49 0.97 0.00015 9.4 0.081 0.053 0.00049 4.10.0051 0.063 0.00037 0.00031 0.000059 0.00061 0.55 0.91 0.00016 9.3 0.07 0.04 0.00052 4.20.019 0.055 0.00027 0.00014 0.000016 0.00017 0.07 0.088 <0.00005 3.7 0.0064 0.0037 0.00021 1.7

0.055 0.024 0.001 0.0014 0.0034 1.9 0.011



ANZECC guideline

Sodium

Dissolved

(mg/l)

Sodium

Total

(mg/l)

Zinc

Dissolved

(mg/l)

Boron

Dissolved

(mg/l)

Chloride

(mg/l)

Sulfur

Total

(mg/l)16 11 0.0017 ND 13 3.419 18 0.0026 ND 21 314 11 0.0016 ND 13 3.474 71 0.022 0.044 47 4373 72 0.021 0.044 46 44

13 13 0.0019 ND 14 4.4

13 12 0.0012 0.024 14 4.1

13 14 0.00073 ND 14 4.1

13 12 0.0006 ND 14 410 9.7 0.0003 ND 14 1.413 12 0.0004 ND 13 3.712 12 0.00056 ND 14 3.7

27 0.013 39 5.626 0.0094 38 5.512 <0.0003 14 3.7

12 12 <0.0003 0.022 14 3.518 19 0.0016 0.036 21 2.911 12 <0.0003 0.022 14 3.474 73 0.018 0.041 45 4075 75 0.017 0.04 46 40

13 14 0.0014 0.023 15 4.7

13 13 0.00065 0.023 15 4.5

12 13 0.00065 0.022 14 4.1

12 13 0.00066 0.023 14 49.6 10 0.0017 0.015 14 1.512 13 <0.0003 0.023 14 3.612 12 0.00039 0.023 14 3.726 29 0.0086 0.052 41 6.426 28 0.0087 0.056 38 5.912 13 0.00032 0.023 14 3.6

0.008 0.37


2-34129.00

13/09/2012 95

Appendix 4: Results of water quality monitoring in the Manawatu River upstream and

downstream of the Totara Road wastewater treatment plant (Nov 2011 to May 2012). The

estimates of periphyton cover are the mean of all replicate measurements.

Date Week Site Flow (l/s)

Days since

3x median

Days since

3x median

and <15 FNU

Days since

>110m3/s

Days since

2x median

Temperature

(°C)

DO

Saturation

(%)

Conductivity

(uS/cm) Field pH

NH4-N

(g/m3)

TN

(g/m3)

Nitrate

(g/m3)

SIN

(g/m3)

DRP

(g/m3) TP (g/m3)

Chlorophyll a

(mg/m2)

Instream guidelines 0.9 0.44 0.01 120 / 200

16-Nov-2011 Week 1 1000m u/s 68,519 5 4 3 4 15.6 95.2 161.5 7.6 0.271 0.74 0.618 0.892 0.017 0.032 0.2

23-Nov-2011 Week 2 1000m u/s 106,480 1 0 0 1 14.2 95.5 139.1 7.54 0.223 0.71 0.449 0.673 0.014 0.05 1.1

30-Nov-2011 Week 3 1000m u/s 122,736 5 3 0 4 15.2 96.9 138.2 7.5 0.15 0.92 0.46 0.612 0.027 0.065 0.1

7-Dec-2011 Week 4 1000m u/s 101,363 12 12 7 11 17 88.2 176.9 7.61 <0.0050 0.79 0.56 0.5635 0.019 0.057 4.0

7-Dec-2011 Week 4 1000m u/s 106,967 12 12 7 11

14-Dec-2011 Week 5 1000m u/s 45,805 19 17 14 18 20.9 115.2 195.1 8.28 0.016 0.33 0.21 0.227 0.005 0.0079 25.0

21-Dec-2011 Week 6 1000m u/s 52,755 5 4 3 4 15.8 100.4 168.1 7.83 0.008 0.38 0.25 0.268 0.006 0.012 3.8

29-Dec-2011 Week 7 1000m u/s 27,597 13 12 11 12 20.8 92 208 7.72 0.014 0.38 0.21 0.225 <0.0050 0.005 41.3

5-Jan-2012 Week 8 1000m u/s 80,941 3 1 1 2 18.7 86.6 162.4 7.65 <0.0050 0.78 0.46 0.4635 0.02 0.036 0.8

11-Jan-2012 Week 9 1000m u/s 330,896 0 0 0 0 18.4 92.4 151.4 7.64 <0.0050 1.7 0.47 0.4735 0.025 0.47 0.0

18-Jan-2012 Week 10 1000m u/s 66,880 8 1 2 6 18.7 89.8 170.7 7.5 <0.0050 0.66 0.46 0.4635 0.017 0.034 0.6

18-Jan-2012 Week 10 1000m u/s 65,401 8 1 2 6 19.6 99.6 116.4 7.81 <0.0050 0.66 0.46 0.4662 0.016 0.022

25-Jan-2012 Week 11 1000m u/s 38,534 15 8 9 13 18 100.8 198.6 7.81 <0.0050 0.57 0.36 0.3635 0.007 0.009 13.0

1-Feb-2012 Week 12 1000m u/s 35,585 22 12 4 20 18.1 103.7 188.9 7.76 <0.0050 0.5 0.21 0.2135 0.005 0.012 45.9

8-Feb-2012 Week 13 1000m u/s 29,253 29 19 11 27 18.1 107.8 187.1 7.74 0.008 0.22 0.099 0.108 <0.0050 0.014 52.7

15-Feb-2012 Week 14 1000m u/s 98,695 36 24 18 34 17.8 91.2 163.1 7.7 0.018 0.51 0.18 0.199 0.006 0.017 8.3

15-Feb-2012 Week 14 1000m u/s 103,094 36 24 18 34 18.2 94.4 159.9 8.08 0.022 0.76 0.22 0.2452 0.006 0.098

22-Feb-2012 Week 15 1000m u/s 41,501 43 26 25 41 18.9 116.3 177 7.91 0.011 0.54 0.31 0.3244 0.016 0.037 8.3

29-Feb-2012 Week 16 1000m u/s 33,261 50 31 32 48 16 104.7 174.9 7.94 0.01 0.45 0.26 0.271 0.013 0.016 25.8

7-Mar-2012 Week 17 1000m u/s 91,261 2 32 1 2 16 93.9 174.1 7.63 0.012 0.71 0.53 0.545 0.019 0.029 1.0

7-Mar-2012 Week 17 1000m u/s 91,261 2 32 1 2 15.8 90.7 147.1 7.52 0.01 0.72 0.5 0.511 0.017 0.034

14-Mar-2012 Week 18 1000m u/s 44,783 9 7 8 9 15.1 88.8 183.2 7.68 0.007 0.64 0.5 0.508 0.018 0.02 1.3

21-Mar-2012 Week 19 1000m u/s 599,419 0 0 0 0 14.3 98.2 114 7.75 0.059 1.6 0.25 0.312 0.028 0.85

28-Mar-2012 Week 20 1000m u/s 56,107 5 1 3 4 14.7 98.71 152.8 7.67 0.017 0.5 0.42 0.438 0.014 0.041 0.1

5-Apr-2012 Week 21 1000m u/s 84,107 13 7 11 12 15.3 92 142.3 7.64 0.013 0.42 0.25 0.264 0.01 0.19 0.2

11-Apr-2012 Week 22 1000m u/s 37,703 19 10 5 18 15.7 97 180.5 7.71 0.005 0.44 0.31 0.316 0.014 0.023 2.1

18-Apr-2012 Week 23 1000m u/s 28,095 26 17 12 25 14.5 100.3 212.7 8.26 0.009 0.37 0.22 0.23 0.006 0.02 41.2

24-Apr-2012 Week 24 1000m u/s 22,653 32 23 18 31 13.2 102.6 212.4 8.02 0.008 0.23 0.1 0.109 0.005 0.014 74.8

3-May-2012 Week 25 1000m u/s 31,414 41 31 27 40 164.0

9-May-2012 Week 26 1000m u/s 26,560 47 37 33 46 12.4 118.6 66 8 0.008 0.32 0.074 0.0854 <0.0050 0.012 128.9

16-May-2012 Week 27 1000m u/s 193,809 54 42 0 0 10.7 95.4 68.2 7.22 0.012 0.71 0.21 0.223 0.01 0.25

25-May-2012 Week 28 1000m u/s 35,248 63 49 8 62 11.8 99 198.5 7.59 0.013 0.49 0.35 0.364 0.01 0.015 1.3

16-Nov-2011 Week 1 800m d/s 68,519 5 4 3 4 15.6 94 168.5 7.58 0.274 1 0.633 0.913 0.039 0.066 0.5

23-Nov-2011 Week 2 800m d/s 106,480 1 0 0 1 14.3 94.1 141.4 7.53 0.287 0.91 0.446 0.734 0.028 0.077 2.3

30-Nov-2011 Week 3 800m d/s 122,736 5 3 0 4 14.8 93.8 139.5 7.47 0.013 0.84 0.47 0.484 0.015 0.04 0.3

7-Dec-2011 Week 4 800m d/s 101,363 12 12 7 11 17.1 84.9 182 7.56 0.17 1 0.56 0.734 0.036 0.085 10.6

7-Dec-2011 Week 4 800m d/s 106,967 12 12 7 11 17.7 99.6 216.3 7.96 0.15 0.98 0.49 0.645 0.035 0.071

14-Dec-2011 Week 5 800m d/s 45,805 19 17 14 18 20.4 112.7 198.25 8.24 0.18 0.62 0.24 0.424 0.019 0.036 121.3

21-Dec-2011 Week 6 800m d/s 52,755 5 4 3 4 15.5 95.5 169.6 7.84 0.11 0.5 0.25 0.371 0.015 0.033 74.5

29-Dec-2011 Week 7 800m d/s 27,597 13 12 11 12 21.1 102.6 216.7 7.89 0.4 0.73 0.22 0.625 <0.0050 0.014 239.0

5-Jan-2012 Week 8 800m d/s 80,941 3 1 1 2 18.6 86.2 163.9 7.6 0.07 0.9 0.45 0.521 0.03 0.051 1.2

11-Jan-2012 Week 9 800m d/s 330,896 0 0 0 0 18.4 93.7 149.3 7.6 <0.0050 1.6 0.47 0.4735 0.025 0.4 0.1

18-Jan-2012 Week 10 800m d/s 66,880 8 1 2 6 18.8 88.5 172.6 7.52 0.13 0.85 0.46 0.591 0.026 0.051 0.2

18-Jan-2012 Week 10 800m d/s 65,401 8 1 2 6 19.7 116.1 216.1 7.81 0.096 0.79 0.42 0.525 0.028 0.05

25-Jan-2012 Week 11 800m d/s 38,534 15 8 9 13 18.1 98.6 200.2 7.83 0.6 0.75 0.36 0.9672 0.012 0.017 46.4

1-Feb-2012 Week 12 800m d/s 35,585 22 12 4 20 18 98 190.5 7.63 0.074 0.75 0.22 0.3012 0.005 0.017 329.7

8-Feb-2012 Week 13 800m d/s 29,253 29 19 11 27 18.6 113.9 196.1 7.97 0.19 0.47 0.098 0.2974 0.007 0.016 149.2

15-Feb-2012 Week 14 800m d/s 98,695 36 24 18 34 17.8 91.1 162.3 7.69 0.19 0.66 0.18 0.377 0.012 0.077 5.2

Date Week Site Flow (l/s)

Days since

3x median

Days since

3x median

and <15 FNU

Days since

>110m3/s

Days since

2x median

Temperature

(°C)

DO

Saturation

(%)

Conductivity

(uS/cm) Field pH

NH4-N

(g/m3)

TN

(g/m3)

Nitrate

(g/m3)

SIN

(g/m3)

DRP

(g/m3) TP (g/m3)

Chlorophyll a

(mg/m2)

15-Feb-2012 Week 14 800m d/s 103,094 36 24 18 34 20.3 92.4 171.2 8.04 0.23 0.77 0.24 0.4764 0.015 0.059

22-Feb-2012 Week 15 800m d/s 41,501 43 26 25 41 18.6 101.9 182.4 7.66 0.24 0.78 0.32 0.572 0.037 0.073 76.0

29-Feb-2012 Week 16 800m d/s 33,261 50 31 32 48 15.6 93.8 177.7 7.67 0.19 0.57 0.27 0.465 0.014 0.02 45.5

7-Mar-2012 Week 17 800m d/s 91,261 2 32 1 2 15.6 90.8 159.7 7.44 0.11 0.79 0.5 0.611 0.027 0.046 0.1

7-Mar-2012 Week 17 800m d/s 91,261 2 32 1 2 15.7 93.7 180.6 7.45 0.13 0.82 0.51 0.643 0.028 0.052

14-Mar-2012 Week 18 800m d/s 44,783 9 7 8 9 14.9 86 196.2 7.58 0.2 0.76 0.51 0.7139 0.034 0.045 24.0

21-Mar-2012 Week 19 800m d/s 599,419 0 0 0 0 14.2 98.6 113.3 7.73 0.069 1.6 0.26 0.3321 0.026 0.9

28-Mar-2012 Week 20 800m d/s 56,107 5 1 3 4 15.6 88.9 174.8 7.58 0.15 0.63 0.42 0.5741 0.027 0.049 2.2

5-Apr-2012 Week 21 800m d/s 84,107 13 7 11 12 15.3 91.7 166.7 7.63 0.11 0.59 0.33 0.4427 0.02 0.11 0.6

11-Apr-2012 Week 22 800m d/s 37,703 19 10 5 18 15.7 95.9 193.5 7.58 0.21 0.67 0.31 0.5247 0.016 0.024 36.3

18-Apr-2012 Week 23 800m d/s 28,095 26 17 12 25 14.6 105.4 211.7 8.53 0.035 0.38 0.23 0.2678 0.006 0.01 225.9

24-Apr-2012 Week 24 800m d/s 22,653 32 23 18 31 12.8 96.1 228.5 7.73 0.25 0.56 0.12 0.3744 0.009 0.019 417.8

3-May-2012 Week 25 800m d/s 31,414 41 31 27 40 355.5

9-May-2012 Week 26 800m d/s 26,560 47 37 33 46 12 97.2 218.5 7.46 0.51 0.75 0.11 0.6251 <0.0050 0.027 562.9

16-May-2012 Week 27 800m d/s 193,809 54 42 0 0 10.8 94.8 102.4 7.31 0.095 0.99 0.21 0.306 0.014 0.29

25-May-2012 Week 28 800m d/s 35,248 63 49 8 62 11.3 97.3 203.8 7.5 0.27 0.82 0.35 0.6239 0.015 0.024 30.6

16-Nov-2011 Week 1 1400m d/s 68,519 5 4 3 4 15.2 95.4 154.3 7.59 0.14 0.95 0.579 0.723 0.03 0.068

23-Nov-2011 Week 2 1400m d/s 106,480 1 0 0 1 14.3 90.9 137.3 7.52 0.089 0.79 0.436 0.526 0.019 0.068

30-Nov-2011 Week 3 1400m d/s 122,736 5 3 0 4 15.9 81.31 140.6 7.37 0.059 0.84 0.46 0.52 0.019 0.054

7-Dec-2011 Week 4 1400m d/s 101,363 12 12 7 11 17 85.4 175.7 7.59 0.061 0.86 0.55 0.614 0.025 0.07

14-Dec-2011 Week 5 1400m d/s 45,805 19 17 14 18 20.2 111.6 195.4 8.21 0.096 0.49 0.25 0.35 0.011 0.02 79.9

21-Dec-2011 Week 6 1400m d/s 52,755 5 4 3 4 16.3 102.1 167.4 7.98 0.019 0.37 0.24 0.269 0.008 0.011 64.3

29-Dec-2011 Week 7 1400m d/s 27,597 13 12 11 12 21.9 123 209.8 8.39 0.2 0.61 0.21 0.417 <0.0050 0.009 93.9

5-Jan-2012 Week 8 1400m d/s 80,941 3 1 1 2 18.7 83.2 162.7 7.66 0.03 0.8 0.47 0.501 0.026 0.041 0.2

11-Jan-2012 Week 9 1400m d/s 330,896 0 0 0 0 18.5 91.9 154.6 7.67 <0.0050 1.8 0.44 0.4435 0.027 0.46 0.2

18-Jan-2012 Week 10 1400m d/s 66,880 8 1 2 6 19.2 85.8 171.5 7.57 0.072 0.76 0.46 0.533 0.021 0.039 0.4

25-Jan-2012 Week 11 1400m d/s 38,534 15 8 9 13 20.1 119.5 200.7 8.03 0.14 0.63 0.35 0.5 0.01 0.014 29.4

1-Feb-2012 Week 12 1400m d/s 35,585 22 12 4 20 18.2 103.8 188 7.94 0.27 0.62 0.22 0.4991 0.005 0.017 180.9

8-Feb-2012 Week 13 1400m d/s 29,253 29 19 11 27 19.4 125.2 192.8 8.38 0.24 0.4 0.094 0.348 0.007 0.013 289.0

15-Feb-2012 Week 14 1400m d/s 98,695 36 24 18 34 18.9 92.5 162.2 7.78 0.1 0.66 0.19 0.297 0.009 0.073

22-Feb-2012 Week 15 1400m d/s 41,501 43 26 25 41 19 111.8 179.2 7.79 0.19 0.69 0.31 0.5096 0.032 0.054 16.5

29-Feb-2012 Week 16 1400m d/s 33,261 50 31 32 48 16.8 102.7 176.4 7.94 0.16 0.56 0.26 0.427 0.014 0.015 34.6

7-Mar-2012 Week 17 1400m d/s 91,261 2 32 1 2 17 86.2 160.8 7.44 0.079 0.8 0.5 0.58 0.022 0.047 0.2

14-Mar-2012 Week 18 1400m d/s 44,783 9 7 8 9 15.7 86.2 184 7.64 0.13 0.77 0.5 0.6346 0.029 0.035 0.7

21-Mar-2012 Week 19 1400m d/s 599,419 0 0 0 0 14.4 98.9 114.9 7.75 0.068 1.6 0.25 0.3213 0.028 0.89

28-Mar-2012 Week 20 1400m d/s 56,107 5 1 3 4 15.7 88.2 173.3 7.71 0.097 0.7 0.41 0.5099 0.021 0.043 0.1

5-Apr-2012 Week 21 1400m d/s 84,107 13 7 11 12 15.2 91.7 167 7.67 0.056 0.5 0.31 0.367 0.016 0.053 0.2

11-Apr-2012 Week 22 1400m d/s 37,703 19 10 5 18 15.9 99.3 191.9 7.75 0.13 0.63 0.31 0.4448 0.016 0.024 8.3

18-Apr-2012 Week 23 1400m d/s 28,095 26 17 12 25 89.7

24-Apr-2012 Week 24 1400m d/s 22,653 32 23 18 31 13.5 115.2 225 8.42 0.14 0.42 0.11 0.2565 0.007 0.019 276.9

3-May-2012 Week 25 1400m d/s 31,414 41 31 27 40 289.5

9-May-2012 Week 26 1400m d/s 26,560 47 37 33 46 12.7 128.6 215.9 8.32 0.29 0.45 0.091 0.3886 0.005 0.028 291.0

16-May-2012 Week 27 1400m d/s 193,809 54 42 0 0 10.7 94.4 102.7 7.33 0.057 0.72 0.23 0.288 0.007 0.22

25-May-2012 Week 28 1400m d/s 35,248 63 49 8 62 11.1 95.9 199.1 7.51 0.12 0.7 0.36 0.4837 0.012 0.02 57.7

Date

16-Nov-2011

23-Nov-2011

30-Nov-2011

7-Dec-2011

7-Dec-2011

14-Dec-2011

21-Dec-2011

29-Dec-2011

5-Jan-2012

11-Jan-2012

18-Jan-2012

18-Jan-2012

25-Jan-2012

1-Feb-2012

8-Feb-2012

15-Feb-2012

15-Feb-2012

22-Feb-2012

29-Feb-2012

7-Mar-2012

7-Mar-2012

14-Mar-2012

21-Mar-2012

28-Mar-2012

5-Apr-2012

11-Apr-2012

18-Apr-2012

24-Apr-2012

3-May-2012

9-May-2012

16-May-2012

25-May-2012

16-Nov-2011

23-Nov-2011

30-Nov-2011

7-Dec-2011

7-Dec-2011

14-Dec-2011

21-Dec-2011

29-Dec-2011

5-Jan-2012

11-Jan-2012

18-Jan-2012

18-Jan-2012

25-Jan-2012

1-Feb-2012

8-Feb-2012

15-Feb-2012

PSI PPI (%)

Algae

filamentous

>2cm (%)

Algae

mats

>3mm

(%)

Algae

films

(%)

E. coli

(MPN/100ml)

Dissolved

Al (g/m3)

Dissolved

B (g/m3)

Dissolved

Cu (g/m3)

Dissolved

Fe (g/m3)

Dissolved

Ni (g/m3)

Dissolved

Zn (g/m3)

30.0 60.0 260 / 550 0.055 0.37 0.0014 0.011 0.008

460 0.0028

1800 0.12 0.019 0.0008 0.29 0.0005 0.0016

2200 0.043 0.016 0.00087 0.11 0.00036 0.00039

2400 0.038 0.019 0.00062 0.11 0.00034 <0.0003

0.035 0.02 0.00077 0.1 0.00038 <0.0003

24.7 7.4 7.4 0.0 90.9 45895 0.012 0.026 0.00041 0.056 0.00025 <0.0003

16.7 0.2 0.2 0.0 82.8 52913 0.013 0.023 0.00044 0.061 0.00025 <0.0003

18.1 6.0 0.8 5.3 74.7 14 0.0015 0.029 0.00034 0.0073 0.00021 <0.0003

610 0.025 0.025 0.00065 0.11 0.00037 <0.0003

2400 0.11 0.026 0.0011 0.17 0.00062 <0.0003

180 0.023 0.023 0.0006 0.086 0.00035 <0.0003

93 <0.05 <0.05 <0.002 0.057 <0.001 <0.001

16.4 0.5 0.4 0.2 79.3 41 0.0081 0.025 0.00043 0.052 0.00024 <0.0003

17.4 0.8 0.5 0.3 83.2 67 0.0092 0.024 0.00039 0.044 <0.0002 0.00033

20.5 2.5 1.9 0.6 91.7 72 0.0033 0.022 <1e-005 0.028 <0.0002 <0.0003

310 0.028 0.019 0.00013 0.058 0.00023 <0.0003

3900 0.046 0.023 0.00042 0.042 0.00026 0.0021

19.0 0.9 0.9 0.0 90.3 650 0.019 0.021 0.00032 0.054 <0.0002 <0.0003

19.5 1.6 1.5 0.0 89.9 64 0.0091 0.021 0.00034 0.062 0.0002 <0.0003

1.0 0.1 0.0 0.1 4.9 770 0.06 0.019 0.00054 0.093 0.00032 0.0017

980 0.034 0.024 0.0005 0.091 0.00029 0.00038

5.5 0.0 0.0 0.0 27.4 120 0.012 0.026 0.00039 0.067 0.00021 <0.0003

20000 0.19 0.014 0.0013 0.2 0.00066 0.00044

0.0 0.0 0.0 0.0 0.0 310 0.023 0.019 0.00018 0.079 0.0003 <0.0003

0.3 0.0 0.0 0.0 1.4 1400 0.066 0.014 0.00067 0.091 0.0003 <0.0003

5.9 0.7 0.6 0.0 26.7 150 0.01 0.018 0.00043 0.057 0.00026 0.00058

19.3 0.0 0.0 0.0 96.5 68

26.3 10.1 9.9 0.1 86.5 58 0.003 0.022 0.00013 0.043 0.00021 0.00058

30.2 17.2 17.1 0.1 82.0 0.0046 0.02 0.00032 0.038 <0.0002 <0.0003

33.3 22.1 22.1 0.0 77.9 110 0.0017 0.022 0.00018 0.014 <0.0002 0.00045

190 0.14 0.012 0.0007 0.16 0.00032 0.00049

7.4 0.2 0.2 0.0 36.4 84 0.0055 0.02 0.00016 0.045 0.00022

200 0.0015

2000 0.13 0.018 0.0008 0.3 0.0005 0.0016

870 0.048 0.015 0.0011 0.12 0.00035 0.00043

2000 0.043 0.019 0.00066 0.11 0.00035 0.00037

2000 0.035 0.019 0.00072 0.11 0.00036 <0.0003

62.3 56.6 56.6 0.0 43.4 120 0.014 0.025 0.0005 0.054 0.00027 <0.0003

33.8 21.7 21.7 0.0 72.3 110 0.014 0.023 0.00048 0.061 0.00027 <0.0003

56.4 46.6 42.8 3.8 51.4 16 0.024 0.029 0.0003 0.0043 0.00022 <0.0003

550 0.027 0.025 0.00065 0.11 0.00054 <0.0003

2000 0.11 0.025 0.0011 0.18 0.00065 <0.0003

220 0.023 0.023 0.0006 0.085 0.00035 <0.0003

140 <0.05 <0.05 <0.002 0.038 <0.001 <0.001

31.8 18.7 14.9 3.8 80.2 52 0.011 0.025 0.00043 0.053 0.00026 <0.0003

45.9 41.6 36.1 5.5 58.4 99 0.02 0.024 0.0004 0.042 0.00022 <0.0003

46.6 41.2 32.0 9.2 58.8 110 0.019 0.022 5.60E-05 0.028 <0.0002 <0.0003

1300 0.043 0.018 0.00015 0.066 0.00024 0.0011

Date

15-Feb-2012

22-Feb-2012

29-Feb-2012

7-Mar-2012

7-Mar-2012

14-Mar-2012

21-Mar-2012

28-Mar-2012

5-Apr-2012

11-Apr-2012

18-Apr-2012

24-Apr-2012

3-May-2012

9-May-2012

16-May-2012

25-May-2012

16-Nov-2011

23-Nov-2011

30-Nov-2011

7-Dec-2011

14-Dec-2011

21-Dec-2011

29-Dec-2011

5-Jan-2012

11-Jan-2012

18-Jan-2012

25-Jan-2012

1-Feb-2012

8-Feb-2012

15-Feb-2012

22-Feb-2012

29-Feb-2012

7-Mar-2012

14-Mar-2012

21-Mar-2012

28-Mar-2012

5-Apr-2012

11-Apr-2012

18-Apr-2012

24-Apr-2012

3-May-2012

9-May-2012

16-May-2012

25-May-2012

PSI PPI (%)

Algae

filamentous

>2cm (%)

Algae

mats

>3mm

(%)

Algae

films

(%)

E. coli

(MPN/100ml)

Dissolved

Al (g/m3)

Dissolved

B (g/m3)

Dissolved

Cu (g/m3)

Dissolved

Fe (g/m3)

Dissolved

Ni (g/m3)

Dissolved

Zn (g/m3)

1700 0.036 0.025 0.00049 0.035 0.00027 0.0029

30.2 15.2 9.5 5.7 80.5 440 0.018 0.022 0.00034 0.054 <0.0002 0.00032

29.4 12.3 7.9 4.4 85.6 59 0.013 0.024 0.00032 0.059 0.00021 0.00061

3.8 1.3 0.1 1.2 16.2 730 0.041 0.023 0.0006 0.1 0.00033 0.00041

730 0.04 0.019 0.00051 0.1 0.00032 0.0016

19.1 3.4 2.1 1.3 80.6 120 0.01 0.025 0.00033 0.059 0.0002 <0.0003

190 0.16 0.014 0.0012 0.17 0.00062 0.00035

0.2 0.0 0.0 1.2 440 0.022 0.02 0.0002 0.078 0.0003 <0.0003

13.4 3.6 3.3 0.3 52.5 1000 0.045 0.016 0.00063 0.072 0.00028 0.00038

29.0 13.6 7.9 5.7 84.2 140 0.016 0.018 0.00045 0.053 0.00032 0.0012

49.2 36.9 34.4 2.5 61.5 68

68.1 62.6 56.2 6.4 36.8 66 0.02 0.023 0.00012 0.037 0.00021 0.0019

63.9 71.3 66.6 4.7 28.7 0.021 0.021 0.00033 0.035 <0.0002 0.00036

64.3 73.0 70.0 3.0 27.0 130 0.029 0.022 0.00017 0.017 <0.0002 0.001

2000 0.13 0.013 0.00075 0.15 0.00033 0.00071

23.5 5.5 3.1 2.4 91.5 140 0.019 0.021 0.00018 0.048 0.00023 0.00062

5800 0.0029

2300 0.13 0.018 0.0008 0.31 0.0005 0.0014

1400 0.035 0.014 0.00084 0.1 0.00033 <0.0003

3600 0.04 0.019 0.00062 0.11 0.00034 <0.0003

48.7 42.0 42.0 0.0 56.0 100 0.014 0.025 0.00045 0.053 0.00027 0.00044

26.5 10.1 10.1 0.0 83.9 93 0.015 0.023 0.00055 0.059 0.00029 0.00045

55.9 59.6 59.4 0.3 40.4 17 0.022 0.029 0.00032 0.0055 0.0002 <0.0003

390 0.026 0.024 0.00065 0.11 0.00039 <0.0003

2400 0.16 0.026 0.0012 0.18 0.0007 <0.0003

160 0.023 0.022 0.00061 0.083 0.00036 <0.0003

21.6 2.8 2.8 0.0 97.0 47 0.011 0.024 0.00047 0.05 0.00026 <0.0003

35.3 25.6 25.6 0.0 73.8 91 0.016 0.023 0.0004 0.043 0.00021 <0.0003

31.0 18.9 18.9 0.0 79.2 39 0.018 0.021 <1e-005 0.028 <0.0002 <0.0003

0.0 280 0.049 0.018 0.00015 0.074 0.00026 0.00063

23.5 7.1 7.1 0.0 89.3 290 0.018 0.02 0.00031 0.051 <0.0002 0.00043

21.0 2.0 2.0 0.0 95.2 88 0.012 0.023 0.00036 0.058 0.00021 0.0003

920 0.037 0.023 0.00055 0.092 0.00032 0.00044

4.5 0.0 0.0 0.0 22.5 110 0.012 0.025 0.00037 0.063 0.0002 0.00042

2400 0.19 0.013 0.0012 0.19 0.00063 0.00047

0.0 0.0 0.0 0.0 0.0 250 0.023 0.019 0.00019 0.081 0.00032 <0.0003

4.8 0.0 0.0 0.0 23.8 730 0.041 0.016 0.00052 0.072 0.00029 <0.0003

21.3 3.3 3.1 0.3 93.7 170 0.016 0.02 0.00048 0.064 0.00029 0.0027

36.2 22.1 22.1 0.0 78.0

75.7 83.0 83.0 0.0 17.0 76 0.018 0.022 0.00015 0.037 0.00022 0.00041

59.5 65.8 65.8 0.0 34.3 0.021 0.02 0.00033 0.034 <0.0002 0.00035

59.5 65.8 65.8 0.0 34.3 84 0.04 0.022 0.0002 0.011 <0.0002 0.0004

1600 0.21 0.012 0.0013 0.25 0.00061 0.0042

19.4 2.1 2.1 0.0 88.5 99 0.012 0.02 0.00017 0.043 0.00023 0.00056


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Appendix 5: Results of nutrient diffusing substrate periphyton bioassay

Site and treatment

Chl a (mg/m2)

Pheophytin (mg/m2)

Chl a (mg/m2)

Pheophytin (mg/m2) Site and treatment

Chl a (mg/m2)

Pheophytin (mg/m2)

Chl a (mg/m2)

Pheophytin (mg/m2)

Date Collected Date Collected

Site A - Nitrogen 96.9 13.1 0.6 0.0 Site C - Nitrogen 151.8 0.0 1.1 0.0





Site A - Phosphorus 196.9 0.0 0.0 Site C - Phosphorus 210.4 0.0 0.7 0.0

Site A - Phosphorus 112.4 0.0 0.9 0.0 Site C - Phosphorus 164.9 0.0 0.9 0.1




Site A - N + P 164.9 6.2 0.5 0.1 Site C - N + P 154.2 0.0 0.4 0.0

Site A - N + P 100.6 0.0 0.4 0.2 Site C - N + P 144.7 0.0 0.8 0.0

Site A - N + P 116.5 0.0 0.9 0.0 Site C - N + P 189.8 0.0 0.0

Site A - N + P 120.2 0.0 0.5 0.0 Site C - N + P 158.5 0.0 0.8 0.0

Site A - N + P 126.6 0.0 1.2 0.0 Site C - N + P 158.5 0.0 1.6 0.0

Site A - Control 180.7 6.1 1.0 0.2 Site C - Control 120.5 8.7 1.2 0.0





Site B - Nitrogen 0.5 0.0 Site D - Nitrogen 140.0 0.0 1.7 0.0

Site B - Nitrogen 0.0 Site D - Nitrogen 192.9 0.0 1.7 0.0


Site B - Nitrogen 0.0 Site D - Nitrogen 244.4 16.2 0.7 0.0


Site B - Phosphorus 0.6 0.0 Site D - Phosphorus 202.6 0.0 1.0 0.0




Site B - Phosphorus 1.6 0.0 Site D - Phosphorus 271.0 0.0 0.0

Site B - N + P 3.8 0.0 Site D - N + P 178.4 0.0 1.6 0.0

Site B - N + P 0.9 0.3 Site D - N + P 170.3 0.0 1.6 0.0

Site B - N + P 1.2 0.0 Site D - N + P 206.0 0.0 1.6 0.0

Site B - N + P 1.9 0.0 Site D - N + P 176.4 0.0 1.3 0.0

Site B - N + P 0.7 0.0 Site D - N + P 223.2 0.3 1.9 0.0

Site B - Control 1.1 0.0 Site D - Control 360.1 0.0 1.1 0.0


Site B - Control 0.0 Site D - Control 262.2 10.7 1.0 0.0


Site B - Control 0.8 0.3 Site D - Control 206.3 22.9 0.0

Median for sites Upstream A and B Median for sites Downstream C and DN 126.2 13.5 0.6 0.0 N 172.3 0.0 1.0 0.0

P 113.8 0.0 0.8 0.0 P 204.8 0.0 1.0 0.0

N+P 120.2 0.0 0.9 0.0 N+P 173.3 0.0 1.6 0.0

Control 127.6 1.9 1.0 0.0 Control 221.6 8.7 1.0 0.0

Note: missing values due to damaged filter papers

Tray B stollen during 27th April bioassay.

Based on a 65cm diameter exposed filter paper area = 0.003318 m2.

27/04/2012 3/04/2012 27/04/2012 3/04/2012


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Appendix 6: Impact of the treatment wetland on the Totara Road WWTP discharge

Opus International Consultants Ltd

Page - 1

Whakatane Office Concordia House Pyne Street PO Box 800 Whakatane 3158 New Zealand

Tel +64 7 308 0139 Fax +64 7 308 4757

TO Phil Walker (Palmerston North City Council)

COPY Jon Roygard, Logan Brown (Horizons Regional Council)

FROM Keith Hamill

DATE 9 November 2011

FILE 3-37877.00 004wk

SUBJECT Effect of WWTP wetland pond on dissolved reactive

phosphorus Dear Phil, Jon and Logan

This memo discusses the effect of the wetland pond at the Palmerston North Waste Water Treatment Plant (PNCC WWTP) on dissolved reactive phosphorus concentrations. The wetland pond is an unvegetated pond with a surface area of about 5000 m2 and 1 meter deep. It is the last stage of the PNCC WWTP treatment process with effluent entering via the clarifier and after any phosphorus treatment and after UV treatment.

Flow weighted sampling occurs daily prior to the effluent entering the wetland pond and a daily grab sample is collected after the wetland pond when flow in the river is less than 40 m3/s. I analysed dissolved reactive phosphorus (DRP) data collected between 16 September 2009 and 3 October 2011. The dataset was filtered to only include data where the data was paired (i.e. samples were collected upstream and downstream of the wetland pond on the same day) and where the river flow was less than 37.5 m3/s (to avoid the influence of residual high DRP concentrations in the pond).

Results and discussion

The results of the monitoring are shown in Table 1. These indicate that concentrations of DRP in the effluent are about 24% lower after the wetland during low flow periods when P treatment is occurring. Although there is considerable variability in the data a student t-test found the difference between the means to be statistically significant (p =0.04) and an equivalence test found ‘moderate evidence’ of the difference being in the order of 25%. The DRP in the outlet was less than DRP in the inlet about 64% of the time. Most of the situations where the DRP in the outlet is higher than the inlet DRP can be explained by a time lag in response due to the water residence time of the wetland pond. There is no indication of the wetland pond desorbing phosphorus after treatment for phosphorus.

The additional reduction in DRP due to the wetland pond may be caused by the additional residence time allowing for further precipitation of alum flocs binding phosphorus or it could be due to biological process such as phytoplankton growth converting DRP into organic forms.

Opus International Consultants Ltd

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Table 1: Results of sampling DRP before and after the wetland pond when river flow < 37.5 m3/s.

Statistic Before wetland (flow weighted) After wetland (grab sample)

Sample size 200 200

Mean 0.1475 0.1131

Median 0.1075 0.0820

Standard deviation 0.1484 0.1852

Recommendations

Historical monitoring has been sufficient to rule out the possibility of the wetland pond increasing DRP concentrations in the discharge after treatment. Thus it is recommended that the joint monitoring programme proposed for this summer take samples from after the wetland pond treatment system and does not take any additional samples from before the wetland pond as originally proposed in the monitoring programme.

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