DATASHEET: Nitrate vulnerable zone (NVZ) Eutrophic Waters...

Report for existing Polluted Water Poole Harbour

NVZ Name: Poole Harbour NVZ ID: ET1

DATASHEET:

Nitrate vulnerable zone (NVZ) designation 2017 – Eutrophic Waters (Estuaries and Coastal Waters)

Publication Date: June 2016


Page 2

Introduction

This document provides a summary of the evidence used in proposing an area of land as one which should be, or should continue to be, designated as a Nitrate Vulnerable Zone (NVZ) for the purposes of the Nitrate Pollution Prevention Regulations 2015.

A full description of the methods used in developing the NVZ proposals is set out in the detailed methodology for eutrophication-related NVZs, available via http://apps.environment-agency.gov.uk/wiyby/141443.aspx . These methods were developed under the guidance of a review group convened by the Defra for the last NVZ review (2011-2013), which included representatives from the farming and water industries as well as independent academic experts. Minor refinements to the methods have been made for the current review.

NVZs are areas of land that drain to polluted waters and which contribute to the pollution of those waters. Polluted waters include those which are eutrophic or may in the near future become so if the Regulations were not to apply there.

Eutrophication is defined as “the enrichment of water by nitrogen compounds, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned”.

For both freshwaters and saline waters, a weight-of-evidence based approach to assessing the risks and impacts of eutrophication was employed. The evidence for individual water bodies was assessed against a national suite of criteria for eutrophication in the different categories/ types of water for review. The criteria are both quantitative and qualitative and reflect scientific understanding of the process and effects of eutrophication. They are broken down in the same way for each water category as follows:-

Nutrients

Plants/algae

Secondary and other effects

For each designated or candidate water body which might meet the criteria for eutrophication, a datasheet such as this one was completed, bringing together information about the water body, its catchment, its uses, evidence of eutrophication and the sources of nitrogen input.

This document is a record of the evidence used in the designation process, including results from national monitoring and assessment programmes, and further information supplied by Area staff. The proposals for NVZ designation are made as a result of close working between Area and national Environment Agency teams, with further quality assurance for the eutrophication designations through the use of a national expert panel.

Some features of the maps within this report are based on digital spatial data licensed from the Centre for Ecology and Hydrology, ©.

Please note that any maps shown here have not used detailed field boundaries and therefore represent the indicative 'soft' boundary only. The definitive NVZ area can be seen on the “What’s in Your Backyard” (WIYBY) website ((http://apps.environment-agency.gov.uk/wiyby/141443.aspx).

http://apps.environment-agency.gov.uk/wiyby/141443.aspx





Form A (cover sheet) Page 3

Ref. Code: ET1

EC Urban Waste Water Treatment and Nitrates Directives

Use these forms for existing designations under:

Urban Waste Water Treatment Regulations: Sensitive Areas (Eutrophic); Sensitive Areas (Nitrate);

Nitrates Regulations: Polluted Waters (Eutrophic) leading to Nitrate Vulnerable Zone designation

Form A: Cover Sheet

Existing Sensitive Area (Eutrophic) and/or (Nitrate)/ Polluted Waters (Eutrophic)

Take information for questions 1 – 7 from original candidate reports (if available)

Sensitive Area coverage (highlight appropriate coverage):

England England & Wales

Wales England & Scotland

1) Name of regulator

Environment Agency, South West Region

2) Designated Site name

Poole Harbour

3) Main river catchment

Frome & Piddle

4) Location & extent of Designated Site (Map should be included)

Whole harbour to tidal limit. See Figure 1.

5) Type(s) of water body (Tick all boxes that apply)

Running freshwater

Still freshwater

Y Estuarine water

Coastal water



6) In previous reviews this site was designated as a: (Tick all that apply)

Y Sensitive Area (Eutrophic)

Y Polluted Water (Eutrophic)

Sensitive Area (Nitrate)

7) Summary of qualifying sewage treatment work discharges (i.e. greater than p.e.

10,000) which contribute to the pollution of the sensitive area.

Candidate name:

Name of discharge Direct / Indirect

NGR Population equivalent

Current Treatment Planned Type of TER (N, P, NP)

Level (PRIM, SEC, TER)

if TER enter Type (N, P, NP)

Poole STW Direct SZ 00700 93580 167,000 TER N

Wareham STW Direct SY 93600 88680 16,500 SEC N

Total PE 183,500

8) Executive summary of evidence of change in eutrophic status since designation:

Refer back to key indicators of eutrophication at the time of designation.

When Poole Harbour was designated, the eutrophic status appeared to be getting worse. Average levels of DAIN in the rivers Frome and Piddle had been increasing by about 0.1mg/l each year since 1975. CASI data indicated there had been a significant increase in the intertidal area in Holes Bay covered by macroalgae between 1995 and 1998. Since 2000, DAIN levels in the main contributing catchments of the Rivers Frome and Piddle have remained relatively stable. DAIN recorded in the harbour does not appear to have reduced since monitoring commenced. Primary productivity within the harbour remains predominantly to be macroalgae (chlorophyta) attached to sediment and washed up along the shoreline.

Macroalgae surveys carried out in 2008 and 2009 showed that the extent of macroalgae was above the Urban Waste Water Treatment Directive (UWWTD) assessment criteria. In 2011 and 2015 the annual surveys revealed that algae extent had fallen below this threshold however in 2015 the annual survey was only partially completed and therefore is not directly comparable. Excessive growth is considered to be areas of greater than 25% of the available intertidal habitat (AIH) in which the average macroalgal cover exceeds 25%. Over 30% of the AIH was affected by high macroalgae cover during the 2008 and 2009 summer surveys, this fell to 12% in 2011 and 9% in 2015 (partial survey only). Patches of zostera were found during the 2011 survey in areas where it has not been recorded before. Entrained algae has been consistently recorded in the harbour between years and there is evidence to show that algae persists throughout the winter months in some of the more sheltered areas of the harbour.

On the basis of the evidence summarised in this document the NVZ should remain in place.



Now progress to the relevant form(s) for the Sensitive Area/Polluted Water

Form B – Running Freshwaters (information, data, evidence)

Form C – Still Freshwaters (information, data, evidence)

Form D – Estuarine (transitional) Waters (information, data, evidence)

Form E – Coastal Waters (information, data, evidence)

Form G – Actual effect of nutrient removal at qualifying discharge works


Form D (information, data, evidence) Page 6

Ref. Code: ET1


Form D: Estuarine Waters – Information, data, evidence

Existing Sensitive Area (Eutrophic) / Polluted Waters (Eutrophic)

1) Designated Site name: Poole Harbour (take name from Form A)

2) Define approximate area of estuarine water using grid references:

The PW(E) designation covers the whole of Poole Harbour (see figure 1).

Western edge of Harbour (confluence with Rivers Frome & Piddle) NGR 1: SY9447788315 NGR 2: SY9454487699

Northern edge of Harbour (Litchett Bay & Holes Bay)

NGR 3: SY9727292574 NGR 4: SZ0001792873

End point (Harbour entrance) NGR 5: SZ0372787034 NGR 6: SZ0366186701

Surface area (ha): 3309

3) Attach map showing the SA(E)/PW(E), Water Framework Directive (WFD) waterbodies and locations of chemical sample points, biological sample points, any direct or indirect sewage treatment work discharges, direct or indirect discharges of nitrogen compounds from agricultural sources, and other significant discharges of nitrogen or phosphorus e.g. industrial.

See Figure 1.

4) Approximate retention/flushing time (days):

3 – 4 days for the Harbour, although under low flow conditions this could be longer.

5) Brief description of geo-morphological nature of estuary (e.g. broad and flat, deep and fjord-like, salinity regime, stratification etc)

The Harbour is generally fairly shallow, except in the channels dredged for large shipping. Holes Bay, which receives the discharge from Poole STW, is linked to the Harbour by a narrow channel and the exchange rate for Holes Bay is about 1 day. The tidal range in the Harbour is small and is unusual as there are double high waters. There is some evidence to show that stratification occurs in Wareham channel.



6) Summary of main uses and designations: (Tick all boxes that apply)

Y Amenity Y Boating

Y Water sports Y OSPAR problem area

EC Bathing Water Angling

Commercial fishery Y Designated EC Shellfish Water

Y Designated EC Shellfish Harvesting Area

Non - designated shellfish harvesting area

Other uses or designations: (specify)

1. 2.

3. 4.

7) If waterbody has conservation status provide details

POOLE HARBOUR Special Protection Area (SPA)(EC Birds Directive)

POOLE HARBOUR Ramsar (wetland of international importance designated under the Ramsar Convention)

POOLE HARBOUR Site of Special Scientific Interest (Wildlife and Countryside Act 1981, as amended)

Poole Harbour is one of the largest natural harbours in the world, a very high proportion of its area comprising intertidal marshes and mudflats. These, together with the permanent channels, support large numbers of wintering wildfowl and waders, for which Poole Harbour has national and international significance.

The SPA is a Protected Area under the EC Water Framework Directive and Marine Protected Area (MPA) under the EC Marine Strategy Framework Directive. Natural England advises that eutrophication, due to elevated nitrogen, is a recognised cause of adverse ecological change in Poole Harbour, particularly through increased macroalgal abundance. The reported MPA target is to restore water quality to mean winter dissolved inorganic nitrogen levels at which biological indicators of eutrophication (opportunistic macroalgal and phytoplankton blooms) do not affect the integrity of the site and features.

8) What chemical data are available? (Tick boxes if evidence is supplied)

Y Dissolved available inorganic phosphorus (DAIP)

Y Dissolved available inorganic nitrogen (DAIN)

Y Chlorophyll-a

Y Cell counts

Y Dissolved Oxygen



Figure 1



Chemical data: summary statistics of samples 2012-2015:

Sample point Year Number of samples

Mean SD Min Max Exceeds WFD criteria

DAIN (uM)*

Poole 1 – Wareham Channel (50900387)

2012-2015 10 291 120 115 501 Y

Poole 3 – Hutchins Buoy (50950249)

2012-2015 10 155 98 39 385 Y

Poole 4 – Poole Bridge (50950217)

2012-2015 10 85 30 46 147 Y

Poole 6 – Nr Buoy 36 (50950125)

2012-2015 10 62 53 20 196 Y

Poole 12 – South Deep (50900149)

2012-2015 10 85 50 44 212 Y

DAIP (uM)


2012-2015 23 0.88 0.32 0.32 1.36 N/A


2012-2015 23 0.67 0.33 0.32 1.32 N/A


2012-2015 23 1.40 0.88 0.32 3.58 N/A

Poole 6 – Nr Buoy 36 (50950125)

2012-2015 23 0.57 0.21 0.32 1.00 N/A


2012-2015 23 0.60 0.32 0.32 1.45 N/A

Chlorophyll-a (ug/l)**


2012-2015 30 6.70 5.48 0.85 22.70


2012-2015 30 4.66 5.00 0.99 23.70


2012-2015 30 3.55 2.85 1.00 14.90

Poole 6 – Nr Buoy 36 (50950125)

2012-2015 30 3.10 2.72 0.79 12.50


2012-2015 30 3.77 3.32 0.51 17.40

Dissolved oxygen – the median values at all sites are greater than 7mg/l during the growing season

*DAIN samples taken 2012-2015 inclusive winter samples only (Nov to Feb)

**Chlorophyll samples taken 2012-2015 inclusive summer samples only (Mar to Oct)

Interpretation and discussion:

Winter DIN levels indicate the Harbour is hyper-nutrified throughout. The highest levels are found at low salinities in Wareham Channel, reflecting the nutrient inputs from the Rivers Frome and Piddle. Winter DIN exceeds the Water Framework Directive (WFD) good/moderate boundary (Figure 2). The change in DAIN over time is shown in Figures 3 and 4 at two sites, Wareham Channel and Poole Bridge. Concentrations



near Poole STW have decreased since nutrient removal was installed at the STW in 2008. DAIN levels in Wareham Channel (which capture the largest proportion of N entering the harbour from the Rivers Frome and Piddle) have increased steadily since 1995. These Figures also show changes in orthophosphate with time as well as the molar ratio of N:P. In addition, the DAIN values have been back-calculated to an effective DAIN concentration at zero salinity (i.e. in freshwater) using the measured salinity of the sample to derive the freshwater fraction.

Chlorophyll-a data indicates that algal blooms above 10ug/l have been recorded Wareham Channel (Figure 6a) and with less frequency at Poole Bridge (Figure 6b). However when a salinity corrected standard is applied there are no criteria exceedances (Figure 5). Phytoplankton growth is not considered a eutrophication problem in Poole Harbour (Figure 12) which is consistent with the evidence at the time of designation, when macroalgae cover rather than phytoplankton status was the primary symptom of eutrophication. The 2001 submission states, “There were few chlorophyll-a exceedences of the DoE standard in the period 1998-2000 and there were no reports of nuisance or potential toxin-producing algae, exceptional blooms, scums or algal mats.”

There have been no known reports to the Environment Agency of toxic algal blooms in the last five years.

Figure 2. Winter DIN (November to February, 2005 - 2015) with the WFD good/moderate boundary shown. All samples are above the good/moderate boundary.



Figure 3. Nutrient concentrations in Wareham Channel (Poole Harbour 1) from 1995. Wareham Channel is in the west of Poole Harbour and is the closest Harbour monitoring point to the Rivers Frome and Piddle. Concentrations of orthophosphate has decreased slightly over this time period the N:P ratio has increased slightly.

Figure 4. Nutrient concentrations at Poole Bridge (Poole Harbour 4) from 1995. Poole Bridge is at the entrance to Holes Bay and is the closest Harbour monitoring point to Poole STW. There appears to be some reduction in DAIN concentration since 2008 corresponding with the start of nutrient removal at Poole STW.



Figure 5. Chlorophyll-a data during the growing season for Poole Harbour (March to October, 2012-2015). The salinity corrected standard is also shown.

Figure 6a. Chlorophyll-a concentrations in Wareham Channel (Poole Harbour 1) from 2000. Wareham Channel is in the west of Poole Harbour and is the closest Harbour monitoring point to the Rivers Frome and Piddle.



Figure 6b. Chlorophyll-a concentrations at Poole Bridge (Poole Harbour 4) from 2000. Poole Bridge is at the entrance to Holes Bay and is the closest Harbour monitoring point to Poole STW.

9) What biological / observational data are available? (Tick boxes if evidence is supplied)

Angiosperms

Y Planktonic algal blooms

Y Macroalgae

Presence of foam / scum

Shellfish / invertebrate / fish mortality

Y Photographs

Interpretation and discussion of biological evidence:

Macroalgae

The summer distribution of macroalgae throughout Poole Harbour has been surveyed in 2008, 2009, 2011 and 2015. The results of quadrat sampling are summarised in tables 1 to 4, and plotted on maps in Figures 7 to 10. The greatest density of macroalgae occurs in the sheltered areas of the Harbour, predominantly the sheltered bays along the southern Purbeck edge of the harbour and Holes Bay to the North. The area of available intertidal habitat of Poole Harbour is estimated to be 1274.5ha. The macroalgae cover recorded in each survey affected 30% of the available intertidal habitat in 2008, 33% in 2009, 12% in 2011 and 9% in 2015 however the 2015 survey was only partially completed. The average macroalgae cover in all sampled patches was greater than 25%.

Algal patches in which the average macroalgae cover exceeds 75%, covered 11% of the AIH in 2008, 15% in 2009, 11% in 2011 and 8% in 2015. Eel grass (Ruppia maritima) was recorded in Newton Bay, Brands Bay, Ower Bay and off Fitzworth Point in 2015 as recorded in previous surveys.

The area affected by macroalgal cover is mapped for 2008 (Figure 7b) and 2015 (Figure 10b). The area affected by macroalgae cover was less during the August 2011 and September 2015 surveys, however in 2015 only 33% of the available intertidal habitat (435.4/1322.0 Ha) was surveyed. Aerial survey data shows coverage at approximately 8.1% of AIH, although coverage from this survey was only 40% because 60%



was obscured by water at the time of the flight. There are 6 sites that have been surveyed in every survey year, and therefore can be used for comparison purposes. These sites are Brands Bay, Holes Bay patch 1, Holes Bay patch 2, Holes Bay patch 3, Newton Bay and Ower & Fitzworth points combined. Percentage cover has increased at every site in most years with the exception of Ower & Fitzpoint points which show a marked reduction in cover in 2009 and again in 2015 to a lesser extent. In contrast biomass shows a much more varied pattern however the highest biomass levels recorded at every site with the exception of Newton Bay occurred in 2008.

In 2015 the percentage cover and biomass of macroalgae in each patch was still high. The average macroalgae cover of all patches in 2015 was 65%, and the average biomass of macroalgae was 786g/m2.

Urban Wastewater Treatment guidance defines excessive macroalgal growth to be areas of greater than 25% of the available intertidal area in which the average macroalgal cover exceeds 25%. Poole Harbour survey results indicate that the percentage cover of macroalgae exceeded this criteria in 2008 and 2009, but was less than this criteria in 2011 and 2015. The likely explanation for this is that in 2011 and 2015 different sites and fewer quadrats were sampled.

Macroalgae in Poole Harbour was also assessed under the Habitats Directive Review of Consents. The Habitats Directive guidance advises that an appropriate assessment should be undertaken if the percentage cover of macroalgae is greater than 15%, or if the percentage cover is greater than 5% and the density of macroalgae is greater than 1000g/m2. Levels of macroalgae in some areas of Poole Harbour exceed the Habitats Directive appropriate assessment trigger in 2008, 2009 and in 2011. The Habitats Directive criteria was not met in 2015 however this is likely due to only a partial survey having been completed (approx 33% AIH surveyed).

Macroalgae in Poole Harbour has also been assessed under the Water Framework Directive. The WFD classification method uses data on percent cover, biomass and the presence of entrained algae. The resulting classification has classed Poole Harbour as moderate for macroalgae every year since baseline classification in 2009.

Overwintering algae

Bi-monthly macroalgae surveys have been carried out at 3 sites (Holes Bay, Brands Bay and Arne Bay) since April 2010 to assess how macroalgal cover and biomass varies over the year and if macroalgae persists through the winter. Macroalgae was found to persist throughout the year at all 3 sites (Figures 11a and 11b). The highest winter percentage cover and biomass results were from Holes Bay which experiences the greatest density of algae throughout the year. Winter macroalgal cover tends to be lower at Brands Bay and Arne Bay. In 2015, the mean algal cover was 3% in February, 100% in May and August and dropped back to 12% in the November survey. The May survey recorded the highest mean biomass at both Holes Bay (3671g/m²) and Brands Bay (1731 g/m²).

In summary, the evidence indicates that macroalgae is still a problem in Poole Harbour based on the combination of percentage cover, biomass, the presence of entrained algae and the algae persisting throughout the winter months. Further monitoring is required to assess the situation in future years following improvements in nutrient management in the Poole Harbour catchment.

Photos taken of Newton Bay from the 2015 annual macroalgae survey are shown in Appendix 1.

Phytoplankton

Phytoplankton data from 2007 to 2014 is shown in Figure 12. Phytoplankton blooms above 5 x 105 cells per litre have occurred in every year from 2007 however phytoplankton classification under the Water Framework Directive has never fallen below good status since it was first classified in 2010.



Table 1. Summary results from the July 2008 Poole Harbour macroalgae survey. The total area affected by over 25% algal cover is 383.8 ha, which equates to 30% of the available intertidal habitat. The AIH is estimated to be 1274.5 ha.

Algal Patch Patch Area (ha)

No. of quadrats in patch

Mean % cover

Mean biomass (g/m2)

% of quadrats containing entrained algae

Arne Bay 17.4 13 55.77 1212.31 15.4

Blue Lagoon 1.9 2 65 4480 50

Brands Bay 101 13 65.54 1298.46 84.6

Green Island 24.3 10 53.6 588 20

Holes Bay patch 1 16 10 70.5 2272 90

Holes Bay patch 2 15.2 10 89 3900 70

Holes Bay patch 3 9.4 7 62.86 2040 57.1

Holes Bay patch 4 7.2 10 80.5 1656 50

Holes Bay patch 5 20.3 15 84.67 2904 40

Holes Bay patch 6 3.8 4 75.5 1110 0

Holton Heath patch 1 34.6 14 49.79 934.57 28.6

Holton Heath patch 2 4.1 6 58.67 1366.67 66.7

Keysworth 3.3 5 62 792 0

Lytchett Bay patch 1 3.6 10 72.2 2060 70

Lytchett Bay patch 2 4.1 5 90 2632 20

Newton Bay 19.3 11 72.36 1192.73 81.8

Ower Bay & Fitzworth 96.2 13 79.54 2196.85 76.9

Parkstone Bay patch 1 1.2 4 68.25 1490 0

Parkstone Bay patch 2 0.6 1 90 800 0

Upper Wytch 0.3 3 70 640 0

Total: 383.8



Table 2. Summary results from the July 2009 Poole Harbour macroalgae survey. The total area affected by over 25% algal cover is 420 ha, which equates to 33% of the available intertidal habitat. The AIH is estimated to be 1274.5 ha.



Mean % cover

Mean biomass (g/m2)

% of quadrats containing entrained algae

Arne Bay 88.6 10 56.5 434 0

Blue Lagoon 3.3 2 100 1450 0

Brands Bay 63.4 10 76.3 1056.4 10

Green Island 19.3 8 38.75 163 0

Holes Bay patch 1 45.7 15 84.67 2215.73 0

Holes Bay patch 2 21.7 10 94.5 2528 10

Holes Bay patch 3 14.1 5 77 840.8 0

Holes Bay patch 4 1.2 2 85 2102 0

Holton Heath patch 1 45.6 10 55.9 663.2 0

Holton Heath patch 2 4.1 5 63 618.4 0

Keysworth 5.7 5 74.6 874.4 0

Lytchett Bay patch 1 3.2 10 77 831.6 0

Lytchett Bay patch 2 1.7 3 53.33 418.67 0

Lytchett Bay patch 3 0.94 3 85 1006.67 0

Newton Bay 33.4 5 86.6 920 0

Ower Bay & Fitzworth 63.8 13 66.15 866.15 0

Upper Wytch 4.5 5 51.4 440.8 0

Total 420.24



Table 3. Summary results from the August 2011 Poole Harbour macroalgae survey. The total area affected by over 25% algal cover is 157 ha, which equates to 12% of the available intertidal habitat. The AIH is estimated to be 1274.5 ha. Patches of eelgrass were recorded in Brands Bay, Newton Bay and Ower Bay and Fitzworth for the first time.



Mean % cover

Mean biomass (g/m2)

% containing entrained algae

Arne Bay 8.3 8 91.51 836 0

Brands Bay 13.3 15 85.18 1271.47 0

Green Island 1.7 5 72.36 996 20

Holes Bay patch 1 24.5 18 83.28 1475.56 5

Holes Bay patch 2 16.9 10 92.84 1195.6 0

Holes Bay patch 3 8.7 7 81.84 1292.57 0

Holes Bay patch 4 4.3 5 100 2014.4 0

Holton Heath 15.2 10 80.51 1201.2 0

Keysworth 7.8 10 73.33 1055.6 0


Lytchett Bay patch 2 5.6 10 88.27 1386 0


Newton Bay 14 10 86.17 476.4 0

Ower Bay & Fitzworth 18.9 11 83.56 1011.24 5

Wytch patch 1 1.8 5 79.04 811.2 0

Wytch patch 2 2.7 5 75.56 545.6 0

Total 157.3



Table 4. Summary results from the September 2015 Poole Harbour macroalgae survey. The total area affected by over 25% algal cover is 117.5 ha, which equates to 9% of the available intertidal habitat.

The AIH is estimated to be 1274.5 ha.



Mean % cover

Mean biomass (g/m2)

% containing entrained algae

Brands Bay 27.1 17 86.3 721 18

Holes Bay patch 1 20.5 8 92.5 1894 63

Holes Bay patch 2 19.5 12 99.0 1909 8

Holes Bay patch 3 8.9 0 N/A N/A N/A

Newton Bay 17.3 16 85.2 1350 6

Ower Point 11.2 10 90.3 1373 0

Fitzworth Point 5.8 8 71.0 1311 13

Gold Point 1 0.1 0 N/A N/A N/A

Gold Point 2 0.2 3 63.3 144 0

Gold Point 3 0.3 2 54.5 164 0

Gold Point 4 1.6 6 38.0 212 0

Hamworthy 1 2.3 5 33.4 138 0

Hamworthy 2 1.6 3 36.3 125 0

Hamworthy 3 1.1 2 29.0 94 0

Total 117.5 92



Figure 7. 2008 Macroalgae survey % cover results.



Figure 7b. 2008 Macroalgal affected area.



Figure 8. 2009 Macroalgae survey - % cover results



Figure 9. 2011 Macroalgae survey.



Figure 10. 2015 Macroalgae survey.



Figure 10b. Area affected by macroalgae in 2015.



Figure 11a: Changes in biomass (g/m²) of opportunistic macroalgae at fixed monitoring points in Holes Bay, Arne Bay and Brands Bay, April 2010 to November 2015. Symbols indicate mean of five quadrats and error bars indicate range.



Figure 11b: Changes in cover (%) of opportunistic macroalgae at fixed monitoring points in Holes Bay, Arne Bay and Brands Bay, April 2010 to November 2015. Symbols indicate mean of five quadrats and error bars indicate range.







Figure 12: Phyoplankton total cell counts at each sampling site 2007 – 2014.



10) Which of the methodology indicators are exceeded?

Y Nitrate concentrations (February nitrate/nitrogen concentrations significantly enhanced)

Y WFD phytoplankton classification of moderate ecological status or worse

Occurrence of unusual algal blooms

Oxygen deficiency (based on WFD and/or UWWT/Nitrate directive methods )

Macroalgae exceeds thresholds (UWWT and WFD)

11) Other evidence of adverse effects on uses and designations:

12) List the current WFD status/potential for any WFD waterbodies within the SA(E)/PW(E

Waterbody ID WaterbodyName Current overall status

Ecological status

Ecological certainty

Status of biological elements sensitive to nutrient enrichment

Status of Phys-chem supporting elements

Phytoplankton Macroalgae Angiosperms Disolved Inorganic Nitrogen

Dissolved Oxygen

GB520804415800

POOLE HARBOUR Moderate Moderate Very certain Good Moderate Moderate High

13) Is/are the WFD waterbody catchment/s in the SA(E)/PW(E) failing or at risk of failing the dissolved inorganic nitrogen standard for WFD?

Poole Harbour transitional waterbody is failing the DIN standard for WFD.



14) Executive summary of the chemical, biological and other evidence illustrating eutrophication in the SA(E)/PW(E)

(See guidance note 27)

Winter DAIN levels exceed the WFD good/moderate boundary and indicate Poole Harbour is hypernutrified throughout. Average levels of DAIN in the Rivers Frome and Piddle increased by approximately 50% in the River Frome and 75% in the River Piddle between 1975 and 2000. Since 2000 the rate of increase has slowed and concentrations have remained relatively stable. DAIN levels recorded in the harbour do not appear to have reduced significantly which reflects trends in the surface water. There is also a large groundwater influence on nutrient levels entering the harbour.

The primary symptom of eutrophication in Poole Harbour is the development of extensive mats of green macroalgae, primarily Enteromorpha spp. and Ulva spp., in intertidal areas subject to reduced tidal flushing including Holes Bay and the more sheltered bays that are located on the southern side of the harbour. Macroalgae in Poole Harbour has been classified as at moderate status under the WFD in every classification year to date. Macroalgae was estimated to cover 30% of the available intertidal habitat (AIH) in 2008 and 33% in 2009, 12% in 2011 and 9% in 2015 though the 2015 survey was only partially complete. The average biomass of macroalgae during the 2008, 2009 and 2011 summer surveys was over 1000g/m2 and 786g/m² in the 2015 partial survey. Entrained algae is present in some areas and there is evidence of algae persisting throughout the winter in Holes Bay, Brands Bay and Arne Bay, where bimonthly monitoring has been carried out since 2010.

15) Summary of eutrophication control measures (already in progress and/or already planned) if any, for the existing area.

Poole Harbour was designated a SA(E) & PW(E) in 2002. Nutrient stripping was installed at Poole STW in 2008. Modelling showed that nutrient removal at Poole STW would have a major effect on DAIN levels in Holes Bay and some impact on DAIN levels in the east Harbour.

Nutrient stripping has not been installed at Wareham STW because modelling predicted that nutrient removal would not effect DAIN levels in the west Harbour. Nutrient levels in the west Harbour are dominated by the input from the Rivers Frome and Piddle.

The catchments draining to Poole Harbour have been designated as an NVZ. This means that specific farming practices are controlled in the designated area to reduce nitrogen losses from agriculture to water.

The NVZ designation:

Requires farmers within the NVZ to reduce nitrate pollution.

The farmers must follow a set of mandatory rules, known as the Action Programme Measures.

The Action Programme Measures are based on Good Agricultural practice and require the careful management and recording of fertiliser and manure use.

A requirement for farms to be able to store slurry for 5 months will come into force in January 2012.


Form G (effects of nutrient reduction) Page 32

Ref. Code: ET1


Form G: Effects of Nutrient Reduction

Existing Sensitive Area (Eutrophic) / Polluted Waters (Eutrophic) 1) Designated Site name: Poole Harbour (take name from Form A)

2) Type(s) of water body: (take info from Form A)

Running freshwater

Still freshwater

Y Estuarine water

Coastal water

3) Summary of qualifying sewage treatment work discharges (copy info from Form A)

Candidate name: <enter name>

Name of qualifying discharge

Direct/Indirect

NGR Population Equivalent

Current level of treatment

(>10,000 PE)

Poole STW Direct SZ 00700 93580 167,000 Tertiary

Wareham STW Direct SY 93600 88680 16,500 Tertiary

Total PE 183,500

Remarks:

4) Summarise the comparative impact of the discharges (e.g. compare chemical and biological data upstream and downstream of the sewage discharge) in relation to pre-designation.

5) Where available provide estimates of nutrient loading for contributions for both qualifying sewage treatment work discharges and agricultural sources. Summarise how this has changed over time.

The Frome and Piddle catchments contribute the greatest percentage DAIN load to Poole Harbour (see figure 13). Agricultural sources of nitrogen are considered to be the most important sources of nitrogen in all river catchments. Trends in nitrogen concentrations in the River Frome and Piddle are shown in Figures 14 and 15. Concentrations in the rivers have been increasing from approximately 4mg/l average DAIN in the 1970s to approximately 6mg/l DAIN now. Since 2000, the profile appears to have levelled off with N levels remaining relatively stable despite some fluctuation between years.

Although diffuse agricultural pressures have reduced over the last 20 years, the slow travel time through the chalk aquifer prevalent throughout South Wessex means that the level of nitrate leaching



through the system is still very high (there is a delay of 30-35 years on average between nitrate leaving the soil zone and entering the harbour). Any biological response to a reduction in nutrient levels is will also involve a time lag.

Poole STW discharges into Holes Bay which is shallow and has a relatively low rate of flushing, therefore the discharge from the STW has a significant impact on the nutrient concentrations within Holes Bay. However the Poole STW discharge along with other direct discharges such as CSO’s and surface water drainage from the urban catchment contribute only 7% of the total DAIN load to the harbour. Nitrogen concentrations from Poole STW have significantly reduced since nutrient removal was installed in 2008 (Figure 16).

Figure 13. Estimated percentage contribution of sub-catchment areas to total annual inorganic nitrogen load on Poole Harbour (taken from Strategy for Managing nitrogen in the Poole Harbour catchment to 2035, Bryan et al., 2013).



Figure 14. Trends in annual average Nitrate the Rivers Frome and Piddle.

Figure 15. Annual average concentrations of DAIN in the main rivers flowing to Poole Harbour.



Figure 16. Annual average concentration of DAIN in Poole STW final effluent.

6) Give a summary of the eutrophication control measures (in progress and/or planned), for the SA(E)/PW(E).

Poole Harbour was designated a SA(E) in 2001, and nutrient stripping was installed at Poole STW in 2008. Modelling showed that nutrient removal at Poole STW would have a major effect on DAIN levels in Holes Bay and some impact on DAIN levels in the east Harbour.

Nutrient stripping at Wareham STW is planned to take place in 2016 driven by the requirements of the Urban Waste Water Treatment Directive. Nutrient was not applied to Wareham STW at the time of designation as modelling at that time predicted that nutrient removal would not effect DAIN levels in the west Harbour, the dominant sources being the Rivers Frome and Piddle. Current source apportionment modelling suggests this is still the case, however stripping is planned to go ahead at this works which is over the population equivalent threshold.

Poole Harbour was also designated a PW(E) in 2001. This subsequently resulted in a NVZ designation in 2002. This means that specific farming practices are controlled in the designated area to reduce nitrogen losses from agriculture to water.

The NVZ designation:

Requires farmers within the NVZ to reduce nitrate pollution.

The farmers must follow a set of mandatory rules, known as the Action Programme Measures.

The Action Programme Measures are based on Good Agricultural practice and require the careful management and recording of fertiliser and manure use.

A requirement for farms to be able to store slurry for 5 months will come into force in January 2012.

7) If the SA(E)/PW(E) has previously been designated, is there any evidence to suggest that its status has changed (e.g. it is no longer eutrophic) and is this change a result of the control measures put in place, or due to a change in our methods/criteria, since the original designation?



Recorded macroalgae cover was significantly lower in 2011 than in previous surveys carried out since 1995. This may be partly due to control measures put in place, particularly nutrient removal installed at Poole STW in 2008. Other factors such as the cold winter of 2010/2011 may also have impacted on macroalgae growth in 2011. The 2015 macroalgae survey shows a further reduction in macroalgae cover however fewer sites were sampled during this survey compared with previous surveys. Continued monitoring will help determine whether the eutrophic status of the harbour is changing following catchment measures.

8) If control measures where removed, would the area be at risk of becoming eutrophic once more?

It is uncertain whether the 2011 and 2015 survey results indicate a change in eutrophic status, or whether macroalgal growth is impacted by other factors including temperature for example, therefore removal of control measures is not advised. Future monitoring should qualify these questions.

References

Bryan, G., D. Kite, R. Money, P. Jonas and R. Barden (2013). Strategy for Managing Nitrogen in the Poole Harbour Catchment to 2035. Environment Agency, pp 222.


Appendices Page 37

Appendix 1. Photos of Newton Bay taken during the Poole Harbour macroalgae survey - September 2nd 2015.


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