Nitrate vulnerable zone designation (NVZ) 2017 Eutrophic waters (Lakes) There are multiple waterbodies in this NVZ, please use the bookmarks on the left toolbar to navigate between waterbodies
Nitrate Vulnerable Zone (NVZ)
designation, 2017 Eutrophication (lakes)
Publication Date: June 2016
Page 1 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
Evidence of eutrophication 2017
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. An accompanying guide to these datasheets is available, which provides an explanation of the contents, acronyms and technical terms.
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).
Page 2 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
46526WB ID: 2013 NVZ status: Not Designated
Section 1. Lake and catchment characteristics
Devon and Cornwall
176134
18
Yes
Moderate alkalinity,shallow,small,lowland
EA Area
Lake grid co-ordinates (Easting/Northing)
Lake waterbody area (ha)
Is the lake heavily modified according to WFD?
WFD Lake Typology
Lake attributes
32358/
Lake Alkalinity (ueq/L) 435
Mean lake depth (m) 4.8
Does stratification occur? Not knownYesIs this waterbody a reservoir?
Natural or artificial lake:Natural --- Impounded (concrete gravity dam) in 1941 for public water supply (South West Water). 1302Ml capacity.
Type of artificial lake:n/a
Lake perimeter (% artificial)<20% (Impounded (concrete gravity dam) in 1941 for public water supply (South West Water).)
Significant changes in lake level due to seasonal drawdown:
Y --- PWS reservoir. Fairly even take with summer increases in demand. In 1976 (drought year) reservoir was drawn down to approx 30%. In 2014 reservoir was drawn down to approx 40%. In 2015 reservoir was drawn down to approx 75%.Pumped storage or other reservoir:n/a
Information on abstraction (if available)
Page 3 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
Lake catchment attributes521Lake catchment area (ha)
If pumped, pumped catchment area (ha)
Primarily surface waterHydrological character
Comments on accuracy of lake catchment:Is the map representative of the natural catchment?Yes
Is the map representative of the artficial catchment?
n/a
Please note that the map above has not used the detailed field boundaries and is the indicative 'soft' boundary.
The definitive NVZ area can be seen on the Environment Agency website (www.environment-agency.gov.uk)
Page 4 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
Section II - Waterbody uses
Controlled water (Section 104 of Water Resources Act):
Public Water Supply:YesDrinking Water Protected Area:YesUWWTD designationNoUsed for hydropower or flow regulation:n/a --- No compensation release requirements.
Accessiblity to public:Easily accessible, many visits --- Close to Penryn and Falmouth. Access is actively promoted by South West Lakes Trust. Visitor facilities include car park, WC, picnic area, play area, nature reserve refreshment kiosk and walks.Recreational fishing:Significant benefit --- Well established coarse fishery - Carp, Pike, Tench, Bream, Roach, Rudd, Perch, Eels. Permits are publicly available. The local council is likely to positively regard the benefit to the local community.Contact watersportsNo activity --- Only fishing currently takes place.Nature of watersports (if applicable): ---
Other public benefit visits:
Significant benefit- Bird watching, walking and general recreation. The local council is likely to positively regard the benefit to the local community.
Conservation value of lake:Local --- SWW Identified Special Protection Zone and Nature Reserve (These are areas are deemed by South West Water as high quality conservation value and do not have any recreational activities taking place within them with the exception of footpaths for walkers. At Argal this is the Southern end – 3 hectares of semi-natural and planted broadleaved woodland, including areas of rich bryophyte flora, and wet woodland (BAP Priority Habitat with management plan in place).Habitats Directive site:
Not SPA or SACSPA or SAC for aquatic interest featuresn/a ---
SSSI or local conservation designation:
Description of Aquatic interest features:
Water Supply:
Recreational use:
Conservation status:
Page 5 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
3.3
40
High
High
2011 - 2014
75th percentile annual TON (mg/l)
Total number of TON samples
Confidence of annual 75th %ile TON exceeding 1 mg/l
Confidence of annual 75th %ile TON exceeding 2 mg/l
Date range of TON samples
Total oxidised nitrogen (TON) data
TON monitoring data
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
08/09/2011
08/11/2011
08/01/2012
08/03/2012
08/05/2012
08/07/2012
08/09/2012
08/11/2012
08/01/2013
08/03/2013
08/05/2013
08/07/2013
08/09/2013
08/11/2013
08/01/2014
08/03/2014
08/05/2014
08/07/2014
08/09/2014
08/11/2014
sample date
TO
N m
g/l
81911056
1.8
18
Mean summer TON (mg/l)
Total number of summer TON samples
Section III - Causes - Nutrients
Page 6 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
3
39
High
High
2011 - 2014
Mean annual TN (mg/l)
Total number of TN samples
Confidence of annual mean TN exceeding 1 mg/l
Confidence of annual mean TN exceeding 2 mg/l
Date range of TN samples
Total nitrogen (TN) data
TN monitoring data
0
10
20
30
40
50
60
70
80
90
08/09/2011
08/11/2011
08/01/2012
08/03/2012
08/05/2012
08/07/2012
08/09/2012
08/11/2012
08/01/2013
08/03/2013
08/05/2013
08/07/2013
08/09/2013
08/11/2013
08/01/2014
08/03/2014
08/05/2014
08/07/2014
08/09/2014
08/11/2014
sample date
TN
mg
/l
81911056
Does any other(e.g. EA non-WFD, or third party) monitoring data for the lake provide improved evidence of significantly elevated nutrient nitrogen?
Strengthens --- South West Water's monitoring data for the raw water from Argal Reservoir shows elevated levels of nitrate. The 75th%ile was >2mg N/l in 2013 and 2014.
Page 7 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
44
Poor
100%
2011 - 2014
Annual geometric mean TP (ug/l)
WFD face value TP class
Confidence of moderate or worse TP status
Date range of TP samples
Total phosphorus (TP) data
TP monitoring data
0
500
1000
1500
2000
2500
08/09/2011
08/11/2011
08/01/2012
08/03/2012
08/05/2012
08/07/2012
08/09/2012
08/11/2012
08/01/2013
08/03/2013
08/05/2013
08/07/2013
08/09/2013
08/11/2013
08/01/2014
08/03/2014
08/05/2014
08/07/2014
08/09/2014
08/11/2014
sample date
TP
ug
/l
81911056
Does any other(e.g. EA non-WFD, or third party) monitoring data for the lake provide improved evidence of significantly elevated nutrient phosphorus?Strengthens --- South West Water's monitoring data for the raw water from Argal Reservoir shows elevated levels of total phosphorus
Page 8 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
12728
12037
182
12909
From all agricultural sources
From agricultural sources minus atmospheric deposition
From urban sources
From all sources
From all sources (minus atmospheric deposition)
Nitrogen loading estimates based on catchment map area
3.9
0.1
4
Leached N (kgN/yr)
Conc. (mg/l)
No data
12218 3.8
Nutrient sources
Significance of loading from agricultural sources to the catchment of the lake
Principal source --- The catchment is primarily agricultural in nature, there are no major sewage discharges.
Significance of loading from human habitation to the catchment of the lake
Minor source --- There are no major sewage discharges in the catchment. The exact contribution from sewage discharges is unknown but estimated to be minor.Significance of any other sources of nutrient loading to the lake or its catchment
Local assessment 2015
73Ranking based on nitrogen loading from agricultural sources
NEAP - N assessment 2014
Page 9 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
Section IV - Response - Plants/Algae
22
Poor
100%
9
Annual mean Chlorophyll (ug/l)
WFD face value Chlorophyll class
Confidence of moderate or worse status
Chlorophyll Good/Moderate boundary value
total number of Chlorophyll samples
Chlorophyll data
Chlorophyll monitoring data
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
08/09/2011
08/11/2011
08/01/2012
08/03/2012
08/05/2012
08/07/2012
08/09/2012
08/11/2012
08/01/2013
08/03/2013
08/05/2013
08/07/2013
08/09/2013
08/11/2013
08/01/2014
08/03/2014
08/05/2014
08/07/2014
08/09/2014
08/11/2014
sample date
Ch
loro
ph
yll u
g/l
81911056
39
2011-2014Date range of Chlorophyll samples
Page 10 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
0.14
Poor
100%
2011 - 2013
EQR
WFD face value class
Confidence of moderate or worse status
Date range of samples
Total number of samples/surveys
Phytoplankton (Pluto EQR)
Macrophytes (EQR)
Diatoms (EQR)
No data
No data
No data
-
No data
No data
No data
-
No data No data
Palaeolimnology
No dataChange as Square Chord Distance
Change in Diatom community No data
0Number of years when algal blooms were observed based on reactive monitoring 2010-2015:
Does any other (e.g. EA non - WFD, or third party monitoring data for the lake provide improved evidence of eutrophication? (local judgement)Strengthens evidence --- South West Water's monitoring data for the raw water from Argal Reservoir shows that blue-green algal blooms (>20,000 cells/ml) occurred in every year from 2010-2014. On many occasions the blooms were so intense that they exceeded 200,000 cells/ml. These large and frequent blue-green algal blooms are putting the Argal Reservoir drinking water protected area at risk. The blooms occur at levels which can have adverse effects on human health. Geosmin and methylisoborneol (MIB) are released from the algae which cause taste and odour problems in drinking water. Blue-green algal blooms have resulted in increased levels of treatment at College Water Treatment Works i.e. Increased use of coagulant, polyelectrolyte, powdered activated carbon and chlorination (which may result in the formation of toxic/carcinogenic trihalomethane).
To which biological element(s) does it relate?
Cyanobacteria ---
Evidence that designated aquatic interest features associated with the lake show evidence of eutrophic disturbance? (local judgement)
Strength of evidence (local judgement) --- Local judgement on the evidence of eutrophic disturbanceY, definitely
28
Other responses
Page 11 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
Review of evidence and recommendations
Needs further investigation
Current assessment of weight of evidence supporting
designation in 2017
Comments and decisions
WFD Weight of evidence for eutrophication:
WFD overall ecological status : Poor
Confidence in WFD status : Uncertain
N is significantly elevated (>2mg/l) and ecological evidence suggests eutrophic impact. Check nature of reservoir and water sources re Defra guidance.
Strong evidence supporting designation. Evidence received from Area showing impact ,including algal blooms and effect on use as drinking water source (see questionnaire completed by Area for College reservoir), so recommendation to designate catchment including both Argal and College reservoirs. Clarify detail of catchment boundary compared with Drinking Water Protected Area Safeguard Zone (boundaries aligned). Falls within the wider Fal Estuary NVZ and designation supported by National staff responsible for estuary designation. Panel support designation.
Recommended action : First national panel
Comments from second national panel :
Comments from first panel:
Second national panel
Local summary and recommendation:Environment Agency and South West Water monitoring data shows that the drinking water protected area of Argal Reservoir is eutrophic. There is high confidence that TON exceeds 2mg/l as a 75th %ile, and high confidence that annual mean total nitrogen exceeds 2mg/l. The reservoir is classed as Poor for total phosphorus, chlorophyll and phytoplankton. Blue-green algal blooms occur frequently and as a result are putting the drinking water protected area at risk. Blue-green algal blooms occur at levels which can have adverse effects on human health; geosmin and MIB released from the algae cause taste and odour problems in drinking water. Blue-green algal blooms have resulted in increased levels of treatment at College Water Treatment Works (including increased chlorination which may result in the formation of toxic/carcinogenic trihalomethane). The main source of nitrogen in the catchment is from agriculture. Recommend NVZ designation. Designation would also be appropriate from a general recreation and fishing (but not for contact watersports) /conservation (albeit not aquatic species - wet woodland which can be vulnerable to eutrophic water) perspective - the reservoir is actively used.
Certainty of eutrophication problem based on core WFD tools: Very certain eutrophication problem
Certainty of eutrophication problem based on overall weight of evidence:
Very certain eutrophication problem
Recommendation: Designate
Page 12 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
Final summary (2017)
2008 Decision: Not Designated
2013 Decision: Not Designated
Lake Description:
Argal Reservoir was impounded with a concrete gravity dam in 1941 for public water supply (South West Water) and has a 1302Ml capacity. It is small at around 18ha and relatively shallow with a mean depth of around 4.8m, the alkalinity is moderate. It should be considered in association with the nearby College Reservoir.
Why the lake should be designated as a Polluted Water (eutrophic):
There is no existing NVZ designation in the Argal reservoir catchment. This public supply reservoir is not a Site of Special Scientific Interest (SSSI) but is identified as a nature reserve by South West Water. Nitrogen concentrations exceed the 1-2 mg/l threshold range and there is evidence of ecological impct.. Agriculture is the primary source of nitrogen.
Phosphorus:
The WFD classification for total phosphorus is Poor status.
Nitrogen:
Both the TON and TN mean values are well in excess of the 2 mg/l threshold. TON values decrease through the summer indicating that N is being used by plants, probably by phytoplankton. Minimum values decreased between 2012 and 2014 which suggests that if input of nitrogen is reduced excessive phytoplankton growth could be limited.
Supplementary evidence:
South West Water recorded blue green algal blooms in every year between 2010 and 2014.
Ecological response:
The WFD class is Poor for both chlorophyll, and overall phytoplankton. This indicates excessive phytoplankton growth.
2017 Recommendation: Designate
Page 13 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
Page 14 of 14
NVZ Name: Argal and College Reservoirs NVZ (Argal Reservoir)
NVZ ID: EL134
Nitrate Vulnerable Zone (NVZ)
designation, 2017 Eutrophication (lakes)
Publication Date: June 2016
Page 1 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
Evidence of eutrophication 2017
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. An accompanying guide to these datasheets is available, which provides an explanation of the contents, acronyms and technical terms.
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).
Page 2 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
46516WB ID: 2013 NVZ status: Not Designated
Section 1. Lake and catchment characteristics
Devon and Cornwall
176835
15.8
Yes
Moderate alkalinity,very shallow,small,lowland
EA Area
Lake grid co-ordinates (Easting/Northing)
Lake waterbody area (ha)
Is the lake heavily modified according to WFD?
WFD Lake Typology
Lake attributes
33421/
Lake Alkalinity (ueq/L) 584
Mean lake depth (m) 2
Does stratification occur? Well mixedNoIs this waterbody a reservoir?
Natural or artificial lake:Natural --- Impounded (earth embankment) in 1906 for public water supply (South West Water). 246Ml capacity.
Type of artificial lake:Y
Lake perimeter (% artificial)Natural
Significant changes in lake level due to seasonal drawdown:
Y --- PWS reservoir. Fairly even take with summer increases in demand. In 1976 (drought year) reservoir was drawn down to approx 60%. In 2014 reservoir was drawn down to approx 35%. In 2015 reservoir was drawn down to approx 20%.Pumped storage or other reservoir:n/a
Information on abstraction (if available)
Page 3 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
Lake catchment attributes521Lake catchment area (ha)
If pumped, pumped catchment area (ha)
Primarily surface waterHydrological character
Comments on accuracy of lake catchment:Is the map representative of the natural catchment?Yes --- Should be same approximate catchment as Argal (immediately downstream).
Is the map representative of the artficial catchment?
n/a
Please note that the map above has not used the detailed field boundaries and is the indicative 'soft' boundary.
The definitive NVZ area can be seen on the Environment Agency website (www.environment-agency.gov.uk)
Page 4 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
Section II - Waterbody uses
Controlled water (Section 104 of Water Resources Act):
Public Water Supply:YesDrinking Water Protected Area:YesUWWTD designationNoUsed for hydropower or flow regulation:n/a --- no compensation flow
Accessiblity to public:Easily accessible, many visits --- Close to Penryn and Falmouth. Access is actively promoted by South West Lakes Trust. Visitor facilities include car park, WC, picnic area, play area, nature reserve, refreshment kiosk and walks.Recreational fishing:No activity --- Coarse fishing takes place in neighbouring Argal.Contact watersportsNo activityNature of watersports (if applicable):
Other public benefit visits:
Moderate benefit- Low key use - nature reserve / bird watching / circular walking routes.
Conservation value of lake:Local --- SWW Identified Special Protection Zone and Nature Reserve (These are areas are deemed by South West Water as high quality conservation value and do not have any recreational activities taking place within them with the exception of footpaths for walkers. At College this the fringing wet woodland.Habitats Directive site:
Not SPA or SACSPA or SAC for aquatic interest features
SSSI or local conservation designation:
Description of Aquatic interest features:
Water Supply:
Recreational use:
Conservation status:
Page 5 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
2.8
54
High
High
2010 - 2014
75th percentile annual TON (mg/l)
Total number of TON samples
Confidence of annual 75th %ile TON exceeding 1 mg/l
Confidence of annual 75th %ile TON exceeding 2 mg/l
Date range of TON samples
Total oxidised nitrogen (TON) data
TON monitoring data
0
0.5
1
1.5
2
2.5
3
3.5
4
27/07/2010
27/10/2010
27/01/2011
27/04/2011
27/07/2011
27/10/2011
27/01/2012
27/04/2012
27/07/2012
27/10/2012
27/01/2013
27/04/2013
27/07/2013
27/10/2013
27/01/2014
27/04/2014
27/07/2014
27/10/2014
sample date
TO
N m
g/l
81911034
0.8
24
Mean summer TON (mg/l)
Total number of summer TON samples
Section III - Causes - Nutrients
Page 6 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
2
54
High
Not confident
2010 - 2014
Mean annual TN (mg/l)
Total number of TN samples
Confidence of annual mean TN exceeding 1 mg/l
Confidence of annual mean TN exceeding 2 mg/l
Date range of TN samples
Total nitrogen (TN) data
TN monitoring data
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
27/07/2010
27/10/2010
27/01/2011
27/04/2011
27/07/2011
27/10/2011
27/01/2012
27/04/2012
27/07/2012
27/10/2012
27/01/2013
27/04/2013
27/07/2013
27/10/2013
27/01/2014
27/04/2014
27/07/2014
27/10/2014
sample date
TN
mg
/l
81911034
Does any other(e.g. EA non-WFD, or third party) monitoring data for the lake provide improved evidence of significantly elevated nutrient nitrogen?
Page 7 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
23
Good
25%
2010 - 2014
Annual geometric mean TP (ug/l)
WFD face value TP class
Confidence of moderate or worse TP status
Date range of TP samples
Total phosphorus (TP) data
TP monitoring data
0
10
20
30
40
50
60
70
80
13/01/2010
13/04/2010
13/07/2010
13/10/2010
13/01/2011
13/04/2011
13/07/2011
13/10/2011
13/01/2012
13/04/2012
13/07/2012
13/10/2012
13/01/2013
13/04/2013
13/07/2013
13/10/2013
13/01/2014
13/04/2014
13/07/2014
13/10/2014
sample date
TP
ug
/l
81911034
Does any other(e.g. EA non-WFD, or third party) monitoring data for the lake provide improved evidence of significantly elevated nutrient phosphorus?
Page 8 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
12728
12037
182
12909
From all agricultural sources
From agricultural sources minus atmospheric deposition
From urban sources
From all sources
From all sources (minus atmospheric deposition)
Nitrogen loading estimates based on catchment map area
3.9
0.1
4
Leached N (kgN/yr)
Conc. (mg/l)
No data
12218 3.8
Nutrient sources
Significance of loading from agricultural sources to the catchment of the lake
Principal source --- College Reservoir shares a catchment with Argal reservoir (College is downstream of Argal) which is primarily agricultural in nature. The land immediately around College Reservoir is rural / farmland.
Significance of loading from human habitation to the catchment of the lake
Minor source --- There are no major sewage discharges in the College catchment. There is an urban area to the north of College Reservoir but it is separated from the reservoir by fields and woodland.Significance of any other sources of nutrient loading to the lake or its catchment
Local assessment 2015
73Ranking based on nitrogen loading from agricultural sources
NEAP - N assessment 2014
Page 9 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
Section IV - Response - Plants/Algae
6
High
0%
16
Annual mean Chlorophyll (ug/l)
WFD face value Chlorophyll class
Confidence of moderate or worse status
Chlorophyll Good/Moderate boundary value
total number of Chlorophyll samples
Chlorophyll data
Chlorophyll monitoring data
0
5
10
15
20
25
30
35
40
45
13/01/2010
13/04/2010
13/07/2010
13/10/2010
13/01/2011
13/04/2011
13/07/2011
13/10/2011
13/01/2012
13/04/2012
13/07/2012
13/10/2012
13/01/2013
13/04/2013
13/07/2013
13/10/2013
13/01/2014
13/04/2014
13/07/2014
13/10/2014
sample date
Ch
loro
ph
yll u
g/l
81911034
60
2010-2014Date range of Chlorophyll samples
Page 10 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
No data
Good
0%
No data
EQR
WFD face value class
Confidence of moderate or worse status
Date range of samples
Total number of samples/surveys
Phytoplankton (Pluto EQR)
Macrophytes (EQR)
Diatoms (EQR)
No data
No data
No data
-
No data
No data
No data
-
No data No data
Palaeolimnology
No dataChange as Square Chord Distance
Change in Diatom community No data
No dataNumber of years when algal blooms were observed based on reactive monitoring 2010-2015:
Does any other (e.g. EA non - WFD, or third party monitoring data for the lake provide improved evidence of eutrophication? (local judgement)Strengthens evidence --- South West Water's monitoring data for the raw water from College Reservoir shows that blue-green algal blooms (>20,000 cells/ml) occurred every year from 2010 to 2015, except 2013; blooms occur at levels which can have an adverse effect on human health. On a number of occasions the blooms were so intense that they exceeded 200,000 cells/ml (see graph). South West Water information shows that College Reservoir also suffers from excessive macrophyte growth. This has resulted in an increase in the amount of organic matter accumulating in the reservoir with a concomitant reduction in water storage capacity. As the area of deep water across College Reservoir decreased it became more difficult for South West Water to deploy and operate aeration units in the reservoir. As a result, anoxic conditions now occur at the lake bed due to bacteria decomposing the accumulated organic matter and using up oxygen. These anoxic conditions in turn lead to the release of manganese from the sediments. In addition, as the algae die back they release geosmin and methylisoborneol (MIB). Manganese, geosmin and MIB affect the taste and odour of water and can make it unpalatable. Levels of geosmin are often >10 ng/l and levels of MIB are often above 30 ng/l in the raw water from the reservoir i.e. above the taste and odour threshold of 10 ng/ for geosmin and 5ng/l for MIB. As a result of all of these factors South West Water stopped using College Reservoir in 2006 as a source of raw water for College WTW. Prior to the end of 2006, College Reservoir supplied 20% of the raw water treated at College WTW. The blue-green algal blooms and high levels of MIB and geosmin are putting the drinking water protected area of College Reservoir at risk.
To which biological element(s) does it relate?
More than one (describe)
Evidence that designated aquatic interest features associated with the lake show evidence of eutrophic disturbance? (local judgement)
Strength of evidence (local judgement)
Local judgement on the evidence of eutrophic disturbanceY, definitely
0
Other responses
Page 11 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
Review of evidence and recommendations
Not assessed
Current assessment of weight of evidence supporting
designation in 2017
Comments and decisions
WFD Weight of evidence for eutrophication:
WFD overall ecological status : Moderate
Confidence in WFD status : Not assessed
Not assessed
Discussed supplementary information for College reservoir provided after initial EA Area consultation - agreed strong evidence of impact, including water company information, and agreed designation should cover both College and Argal Reservoirs.
Recommended action : First national panel
Comments from second national panel :
Comments from first panel:
Second national panel
Local summary and recommendation:Environment Agency and South West Water data shows that the drinking water protected area of College Reservoir is eutrophic. TON exceeds 2 mg/l as a 75th %ile and annual mean total nitrogen exceeds 1 mg/l. In 2015 the reservoir was classed as moderate for total phosphorus. Blue-green algal blooms, levels of MIB and geosmin are putting the drinking water protected area at risk. Blue-green algal blooms occur at levels which can have adverse effects on human health; geosmin and MIB occur at levels which affect the taste and odour of water. As a result of the blue-green algal blooms and macrophyte growth South West Water stopped using College Reservoir in 2006 as a source of raw water for College WTW. The main source of nitrogen in the catchment comes from agriculture. College Reservoir shares a catchment with Argal Reservoir which has been recommended for NVZ designation. Therefore recommend NVZ designation for College Reservoir.
Certainty of eutrophication problem based on core WFD tools: not assessed
Certainty of eutrophication problem based on overall weight of evidence:
Recommendation: Designate
Page 12 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
Final summary (2017)
2008 Decision: Not Designated
2013 Decision: Not Designated
Lake Description:
College Reservoir belongs to South West Water but they have not used it as a water source since 2006. The reservoir is small at 15.8 Ha and very shallow with a mean depth of 1.95 m. It should be considered alongside the nearby Argal Reservoir with which it shares a catchment.
Why the lake should be designated as a Polluted Water (eutrophic):
The Argal and College Reservoirs NVZ is a proposed new eutrophic designation. Agriculture is the primary source of nitrogen in the catchment. Nitrogen concentrations are elevated
Phosphorus:
WFD classification for total phosphorus is Good status. There is some indication of re-release from sediment as concentrations tend to increase in summer.
Nitrogen:
The 75th percentile TON concentration was greater than the 2mg/l threshold, and mean annual TN was 2mg/l. TON increases in winter and becomes very low in summer, suggesting that nitrogen is limiting to growth of phytoplankton, and further reduction would result in more limitation.
Supplementary evidence:
Ecological response:
Data not yet retrieved
2017 Recommendation: Designate
Page 13 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
Page 14 of 14
NVZ Name: Argal and College Reservoirs NVZ (College Reservoir)
NVZ ID: EL134
