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Nitrate Vulnerable Zone (NVZ) designation, 2017 Eutrophication (lakes) Publication Date: June 2016 Page 1 of 14 NVZ Name: Horsey Mere NVZ ID: EL104
Nitrate Vulnerable Zone (NVZ)
designation, 2017 Eutrophication (lakes)
Publication Date: June 2016
Page 1 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
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: Horsey Mere
NVZ ID: EL104
35645WB ID: 2013 NVZ status: Designate (Precautionary)
Section 1. Lake and catchment characteristics
Essex Norfolk and Suffolk
644940
32.8
Yes
Brackish,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
322212/
Lake Alkalinity (ueq/L) 2887
Mean lake depth (m) 1.5
Does stratification occur? Well mixedNoIs this waterbody a reservoir?
Natural or artificial lake:
Type of artificial lake:
--- Man made by historical peat diggings.
Lake perimeter (% artificial)
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: Horsey Mere
NVZ ID: EL104
Lake catchment attributes3488Lake catchment area (ha)
If pumped, pumped catchment area (ha)
--- Horsey Mere is predominantly fed by rainwater and water from surface drains. It receives water from the agricultural area to the north via the Brograve pump. Also some inputs from groundwater including a saline influence, Heigham Broad and the river.
Hydrological character
Comments on accuracy of lake catchment:
Is the map representative of the natural catchment?
No --- This lake is in a low gradient system and it appears that the model has not calculated the catchment correctly. Horsey Mere receives some water from the drain to the north of the broad (Waxham New Cut) and from the IDB pump at Brograve. Map attached and data showing some quite high N results at the Brograve pump. Catchment is not accurate: see http://www.wlma.org.uk/uploads/84-BIDB_drainindex.pdf. Catchment amended after discussion 2015.
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: Horsey Mere
NVZ ID: EL104
Section II - Waterbody uses
Controlled water (Section 104 of Water Resources Act):
Yes
Public Water Supply:
NoDrinking Water Protected Area:
NoUWWTD designation
Used for hydropower or flow regulation:
Accessiblity to public:
--- National Trust shop, moorings and restored wind pump.Recreational fishing:
Contact watersports
Nature of watersports (if applicable):
--- Other public benefit visits:
- Bird watching, walking.
Conservation value of lake:
--- Most of the area is managed for nature conservation. The National Trust owns Horsey Mere.Habitats Directive site:
--- The Broads SAC, SPA, RamsarSPA or SAC for aquatic interest features
---
SSSI or local conservation designation:
--- Upper Thurne Broads & Marshes SSSi
Description of Aquatic interest features:
Water Supply:
Recreational use:
Conservation status:
Page 5 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
0.8
59
Not confident
Not confident
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
17/03/2010
17/06/2010
17/09/2010
17/12/2010
17/03/2011
17/06/2011
17/09/2011
17/12/2011
17/03/2012
17/06/2012
17/09/2012
17/12/2012
17/03/2013
17/06/2013
17/09/2013
17/12/2013
17/03/2014
17/06/2014
17/09/2014
sample date
TO
N m
g/l
THR020
0.3
31
Mean summer TON (mg/l)
Total number of summer TON samples
Section III - Causes - Nutrients
Page 6 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
2.2
18
High
Moderate
2013 - 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
14/08/2013
14/09/2013
14/10/2013
14/11/2013
14/12/2013
14/01/2014
14/02/2014
14/03/2014
14/04/2014
14/05/2014
14/06/2014
14/07/2014
14/08/2014
14/09/2014
14/10/2014
14/11/2014
14/12/2014
sample date
TN
mg
/l
THR020
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 --- There are N results from the IDB Brograve pump which drains an area to the north east of Horsey; this water enters Horsey.
Page 7 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
54
Good
17%
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
20
40
60
80
100
120
140
17/03/2010
17/06/2010
17/09/2010
17/12/2010
17/03/2011
17/06/2011
17/09/2011
17/12/2011
17/03/2012
17/06/2012
17/09/2012
17/12/2012
17/03/2013
17/06/2013
17/09/2013
17/12/2013
17/03/2014
17/06/2014
17/09/2014
sample date
TP
ug
/l
THR020
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: Horsey Mere
NVZ ID: EL104
57697
52964
482
62912
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
12
1.1
139.6
Leached N
(kgN/yr)Conc. (mg/l)
121.3
58179 129.1
Nutrient sources
Significance of loading from agricultural sources to the catchment of the lake
--- Agricultural catchment. Natural England gives Water Pollution – Agriculture/Run-off as a reason for SSSI adverse condition.
Significance of loading from human habitation to the catchment of the lake
--- Many unsewered properties in the area.
Significance of any other sources of nutrient loading to the lake or its catchment
Local assessment 2015
23Ranking based on nitrogen loading from agricultural sources
NEAP - N assessment 2014
Page 9 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
Section IV - Response - Plants/Algae
25
Moderate
100%
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
17/03/2010
17/06/2010
17/09/2010
17/12/2010
17/03/2011
17/06/2011
17/09/2011
17/12/2011
17/03/2012
17/06/2012
17/09/2012
17/12/2012
17/03/2013
17/06/2013
17/09/2013
17/12/2013
17/03/2014
17/06/2014
17/09/2014
sample date
Ch
loro
ph
yll u
g/l
THR020
57
2010-2014Date range of Chlorophyll samples
Page 10 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
0.22
Moderate
100%
2013 - 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
78%
2009 - 2009
No data
No data
No data
-
1 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 --- The Broads Authority's macrophyte surveys have shown that there is a low abundance of aquatic plants and low species diversity. The community is typical of a high nutrient system.
To which biological element(s) does it relate?
Macrophytes ---
Evidence that designated aquatic interest features associated with the lake show
evidence of eutrophic disturbance? (local judgement)
- Yes - evidence from Broads Authority macrophyte surveys in addition to EA dataStrength of evidence (local judgement)
--- Local judgement on the evidence of eutrophic disturbance
33
Other responses
Page 11 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
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 : Poor
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. Catchment check needed and further discussion may be required regarding how to treat pumped drainage catchment [drained catchment subsequently checked with EA local staff and confirmed by consultation with IDB].
Recommended action :
First national panel
Comments from second national panel :
Comments from first panel:
Second national panel
Local summary and recommendation:
This lake is currently designated. Additional evidence has been received from the Broads Authority - their macrophyte surveys have shown that there is a low abundance of aquatic plants and low species diversity. The community is typical of a high nutrient system. The catchment of the lake should be extended to include some drained land pumped to the Mere. Other evidence still stands, and continued designation is appropriate.
Certainty of eutrophication problem based on core WFD tools: Quite certain eutrophication problem
Certainty of eutrophication problem based on overall weight of
evidence:
Quite certain eutrophication problem
Recommendation: Continued designation
Page 12 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
Final summary (2017)
2008 Decision: Not designated
2013 Decision: Designate (Precautionary)
Lake Description:
Horsey Mere is high alkalinity, very shallow, well mixed lake created by peat digging. It is predominantly fed by direct rainwater input and water from surface drains. It receives water from the agricultural area to the north via the Brograve pump. Also some inputs from groundwater including a saline influence, Heigham Broad and the river. The Mere is an SSSI. The broads and marshes associated with the upper reaches of the River Thurne form one of the finest examples of an unreclaimed wetland complex in Britain. They are of national and international importance for nature conservation in supporting a wide range of wetland plant communities and associated animal species.
Why the lake should be designated as a Polluted Water (eutrophic):
Horsey Mere is an existing eutrophic waters NVZ designation but as a result of this review the proposed NVZ area has been extended to include the Internal Drainage Board area that drains into the lake. Agriculture is the principal source of nitrogen from the drained catchment. Total nitrogen concentrations are elevated and there is evidence of eutrophic impact on the ecology.
Phosphorus:
The WFD classification for total phosphorus is Good status.
Nitrogen:
75th percentile TON concentration is 0.8 mg/l, and has decreased from 1.5mg/l in the last review. Mean annual TN is above the 1-2 mg/l threshold range at 2.2 mg/l. There were insufficient samples to calculate a reliable mean TN during the previous review period. TON declines to very low levels in most years, suggesting nitrogen limitation is occurring.
Supplementary evidence:
Broads Authority plant surveys show that there is low abundance and species diversity of aquatic plants.
Ecological response:
Chlorophyll, phytoplankton and macrophytes are all at Moderate WFD status indicating that they are being affected by eutrophication.
2017 Recommendation: Continued designation
Page 13 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
Page 14 of 14
NVZ Name: Horsey Mere
NVZ ID: EL104
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