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Nitrate Vulnerable Zone (NVZ) designation, 2017 Eutrophication (lakes) Publication Date: June 2016 Page 1 of 14 NVZ Name: Slapton Ley NVZ ID: EL124
Nitrate Vulnerable Zone (NVZ)
designation, 2017 Eutrophication (lakes)
Publication Date: June 2016
Page 1 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
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: Slapton Ley
NVZ ID: EL124
46472WB ID: 2013 NVZ status: Designate
Section 1. Lake and catchment characteristics
Devon and Cornwall
282361
65.9
No
High alkalinity,very shallow,large,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
43227/
Lake Alkalinity (ueq/L) 1599
Mean lake depth (m) 1.5
Does stratification occur? Well mixed
NoIs this waterbody a reservoir?
Natural or artificial lake:
--- Slapton Ley comprises a shingle barrier beach enclosing a coastal lagoon forming the largest freshwater
lake in Southwest England.
Type of artificial lake:
Lake perimeter (% artificial)
(Mainly natural although there may be some impact from the weir and tunnel.)
Significant changes in lake level due to seasonal drawdown:
Pumped storage or other reservoir:
0
Information on abstraction (if available)
Page 3 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
Lake catchment attributes4636Lake catchment area (ha)
If pumped, pumped catchment area (ha)
Hydrological character
Comments on accuracy of lake catchment:
Is the map representative of the natural catchment?
--- Yes, the map includes the catchmentof the Gara river, which is a major inflow into the lake and was not in
the 2013 catchment area.
Is the map representative of the artficial catchment?
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: Slapton Ley
NVZ ID: EL124
Section II - Waterbody uses
Controlled water (Section 104 of Water Resources Act):
Public Water Supply:
Drinking Water Protected Area:
No
UWWTD designation
No --- Polluted Water (E) candidate submission in 2008.Copy available.
Used for hydropower or flow regulation:
Accessiblity to public:
--- There are three car parks and provision for school trips. The village of Torcross is adjacent to the outlet of the
lake. There are well used walks and trails.
Recreational fishing:
--- Largest fresh water lake in South West. Historic coarse fishery. Fishing halted in 2005 to protect wildfowl.
Contact watersports
--- Guided canoe tours in summer.
Nature of watersports (if applicable):
Other public benefit visits:
- There is a field study centre and it is used for educational visits and research. Significant numbers of
birdwatchers. Naturalist interest is also provided by mammals and rare plants. Landscape value and significant
use by tourists.
Conservation value of lake:
--- Slapton Ley is a unique wetland within Devon Area of Outstanding Natural Beauty. It is split into two leys or
lakes: the Lower Ley is the largest natural freshwater lake in South West England.
Habitats Directive site:
--- SSSI
SPA or SAC for aquatic interest features
--- Slapton Ley is especially important for the abundance and diversity of its aquatic invertebrate fauna.Gastropods
include the rare Segmentina nitida and the uncommon Planorbis laevis, while Dragonflies include the regionally
uncommon Migrant Hawker Aeshna mixta and the Hairy Dragonfly Brachytron pratense.
SSSI or local conservation designation:
--- SSSI and National Nature Reserve. Nature Conservation Review site.
Description of Aquatic interest features:
---
Water Supply:
Recreational use:
Conservation status:
Page 5 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
4.4
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
1
2
3
4
5
6
10/08/2011
10/10/2011
10/12/2011
10/02/2012
10/04/2012
10/06/2012
10/08/2012
10/10/2012
10/12/2012
10/02/2013
10/04/2013
10/06/2013
10/08/2013
10/10/2013
10/12/2013
10/02/2014
10/04/2014
10/06/2014
10/08/2014
10/10/2014
sample date
TO
N m
g/l
70810102
1.5
19
Mean summer TON (mg/l)
Total number of summer TON samples
Section III - Causes - Nutrients
Page 6 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
3.2
42
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
1
2
3
4
5
6
10/08/2011
10/10/2011
10/12/2011
10/02/2012
10/04/2012
10/06/2012
10/08/2012
10/10/2012
10/12/2012
10/02/2013
10/04/2013
10/06/2013
10/08/2013
10/10/2013
10/12/2013
10/02/2014
10/04/2014
10/06/2014
10/08/2014
10/10/2014
10/12/2014
sample date
TN
mg
/l
70810102
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: Slapton Ley
NVZ ID: EL124
58
Moderate
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
50
100
150
200
250
300
350
400
10/08/2011
10/10/2011
10/12/2011
10/02/2012
10/04/2012
10/06/2012
10/08/2012
10/10/2012
10/12/2012
10/02/2013
10/04/2013
10/06/2013
10/08/2013
10/10/2013
10/12/2013
10/02/2014
10/04/2014
10/06/2014
10/08/2014
10/10/2014
10/12/2014
sample date
TP
ug
/l
70810102
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: Slapton Ley
NVZ ID: EL124
128030
124231
519
128549
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
4
Leached N
(kgN/yr)Conc. (mg/l)
11
124750 3.8
Nutrient sources
Significance of loading from agricultural sources to the catchment of the lake
--- There are influences from agriculture.
Significance of loading from human habitation to the catchment of the lake
--- There have also been issues with sewage related discharges in the past. Not known if these have been
addressed> Local information may be available but has not been provided.
Significance of any other sources of nutrient loading to the lake or its catchment
Local assessment 2015
74Ranking based on nitrogen loading from agricultural sources
NEAP - N assessment 2014
Page 9 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
Section IV - Response - Plants/Algae
13
Good
9%
20
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
20
40
60
80
100
120
140
160
180
10/08/2011
10/10/2011
10/12/2011
10/02/2012
10/04/2012
10/06/2012
10/08/2012
10/10/2012
10/12/2012
10/02/2013
10/04/2013
10/06/2013
10/08/2013
10/10/2013
10/12/2013
10/02/2014
10/04/2014
10/06/2014
10/08/2014
10/10/2014
10/12/2014
sample date
Ch
loro
ph
yll u
g/l
70810102
41
2011-2014Date range of Chlorophyll samples
Page 10 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
0.46
Moderate
58%
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)
0.5
Moderate
100%
2008 - 2013
0.8
Good
0.7%
2012 - 2013
3 3
Palaeolimnology
0.76Change as Square Chord Distance
Change in Diatom community Significant Change
1Number 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)
To which biological element(s) does it relate?
---
Evidence that designated aquatic interest features associated with the lake show
evidence of eutrophic disturbance? (local judgement)
Strength of evidence (local judgement)
Yes
Local judgement on the evidence of eutrophic disturbance
--- Local staff suggest this lake may be eutrophic. Speculated impact on fish species from eutrophication.
32
Other responses
Page 11 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
Review of evidence and recommendations
Existing designation - check needed
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 : Very Certain
Existing designation - N remains >2 mg/l and there is evidence of ecological impact for eutrophication.
Recommend continued designation.
Agreed with provisional decision to continue designation. Noted catchment update requred as agreed
with Area and local Natural England staff.
Recommended action :
First national panel
Comments from second national panel :
Comments from first panel:
Second national panel
Local summary and recommendation:
Environment Agency monitoring data shows that Slapton Ley continues to exhibit signs of
eutrophication. There is high confidence that TON exceeds 2mg/l as a 75th %ile, and high confidence
that annual mean total nitrogen exceeds 2mg/l. Slapton Ley is classed as Moderate for total phosphorus
(very certain), phytoplankton and macrophytes. Therefore recommend continued NVZ designation.
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: Continued designation
Page 12 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
Final summary (2017)
2008 Decision: Designated
2013 Decision: Designate
Lake Description:
Slapton Ley comprises a shingle barrier beach enclosing a natural coastal lagoon forming the largest freshwater
lake in Southwest England. It is a high alkalinity, very shallow, well mixed lake. The outlet and levels are
actively managed to maintain the freshwater environment. Slapton is an SSSI and National Nature Reserve and
has significant conservation and amenity value.
Why the lake should be designated as a Polluted Water (eutrophic):
Slapton Ley is within an existing eutrophic waters NVZ designation. The nitrogen concentrations, although
showing evidence of reduction, continue to be above the threshold range for designation, and some of the
biological elements show eutrophication impacts. Continued designation is therefore propsed. In addition, a
review of the designated NVZ catchment area has shown that only part of the relevant catchment was designated
previously, and an extension to the area is proposed.
Phosphorus:
The WFD classification for TP is Moderate status
Nitrogen:
The 75th percentile concentration of TON is 4.4 mg/l, and annual mean TN is 3.2mg/l - both significantly above
the 1-2 mg/l threshold range. There is evidence of a reduction in concentrations since the previous review when
both TON and TN were 5.2 mg/l. TOn declines ot very low levels in the growth season, inidicating nitorgen
limitation to productivity.
Supplementary evidence:
Ecological response:
Chlorophyll is at Good status for WFD while overall phytoplankton and macrophytes are at Moderate status.
Diatoms are at Good Status. Thus there is still evidence of eutrophication impact on some of the biological
elements. Nitrogen may be limiting the phytoplankton productivity in the growth season, as TON
cooncentrations decline to very low levels in the summer.
2017 Recommendation: Continued designation
Page 13 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
Page 14 of 14
NVZ Name: Slapton Ley
NVZ ID: EL124
