Nitrate Vulnerable Zone (NVZ)
designation 2017 Eutrophic waters
(Lakes): Guide to datasheets
Version 1.0, [Publish Date]
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Guide to the 2017 NVZ datasheets for eutrophication (lakes)
This document provides an explanation of the terms and data used in the 2017 NVZ datasheets for
eutrophication (Lakes).
The datasheets are a record of the data and information obtained to support the review of lakes
affected by eutrophication. They have been populated with information from a range of sources,
including EA monitoring archives, WFD classification results, and information provided by EA Area staff
via a structured questionnaire during a national consultation exercise. Where information is not shown
this is because it was not provided from any of the sources used.
The information is given in the same order as it appears in the datasheets. A list of commonly used
abbreviations and acronyms is given at the end of this document.
General
NVZ name: This may be the name of a single lake, or it may be a proposed NVZ covering more than one
lake, in which case the datasheets for each individual lake have been combined in a single pdf
document.
NVZ ID: This is the unique identifier for the proposed NVZ, but note that for existing (2013) designations
the ID will have changed from that used in the last review.
Section 1 Lake and Catchment Characteristics
WBID is a unique lake water body identifier used in the UK Lakes database (this is also the last five digits
of any lake WFD Water Body ID)
2013 NVZ status is the result of the previous review/designation round. In this context “not designated”
may mean either that the lake was considered but had insufficient information to support designation,
or that it was not previously assessed.
Lake attributes table: This table holds basic data on the lake, taken mainly from data assembled by the
EA for WFD purposes. Note that the alkalinity data are given in units of microequivalents per litre,
whereas the EA routine monitoring data are reported as milligrams per litre calcium carbonate. We
multiply milligrams per litre (mg/l) by a factor of 20 to obtain the value in microequivalents per litre
(µeq/l).
Information below the attributes table on the natural or artificial nature of the lake is as provided by
local EA staff during consultation.
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Lake catchment attributes: The catchments are the natural, mostly surface water, hydrological
catchments of the lake, originally derived by a GIS-based digital topographic modelling procedure. The
digitally derived catchments have subsequently been checked by local EA staff, and amendments made
where necessary. For existing NVZs the catchment from the previous review is assumed to be correct
unless otherwise indicated. These maps show the “soft” boundaries for NVZ purposes and are not
therefore definitive. The final “hard” boundaries that form the actual boundary of the proposed NVZ are
available online.
Section 2 Water Body Uses
This section holds information on the uses of the lake for water supply, recreation and conservation
status. Information is as supplied by local EA staff via a structured questionnaire.
Section 3 Causes –nutrients
This section presents the data from routine monitoring programmes, collated and analysed for the
purposes of the NVZ review.
Nutrient concentrations:
Total oxidised nitrogen (TON) and Total nitrogen (TN) are expressed as milligrams per litre nitrogen,
allowing direct comparison (see the eutrophication method document for further explanation of
nitrogen parameters). Data are from the EA’s WIMS water quality archive, covering the time period
2010-2014 inclusive (or whatever part of that time period for which data were available). These are new
data, not used in the previous review. For most lakes monthly samples are available, although in some
cases quarterly monitoring is carried out.
The tables present summary statistical information to enable comparison against the agreed threshold
values (75th percentile TON, and annual mean TN).
The code number in the graphs is the EA Sample Point Code for the sampling location from which lake
water was collected for analysis.
Text below the graphs is taken from local EA staff response to the consultation questionnaire.
Total phosphorus is expressed as micrograms per litre phosphorus. The geometric mean is the summary
statistic used in WFD classification, and the status class and confidence is that produced for WFD
purposes, which is based on 3 years data. In most cases the WFD class was taken from the 2014
classification results, in a few cases where a 2014 result was not available, the 2015 result was used.
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Nutrient sources:
Nitrogen loading estimates are based on ADAS NEAP-N model outputs, calculated for the catchment
area of the lake (see eutrophication method document for further explanation of the NEAP-N model).
They are used as an indicator of agricultural contribution to the nitrogen load to the lake. The lakes
under consideration are ranked according to calculated agricultural loading (1 = highest load), this
simply gives an indication of the relative size of the agricultural contribution across all the lakes
considered.
Local assessment – this text is the response from local EA staff to questions about the contribution of
agriculture within the catchment.
Section 4 Response – plants/algae
Chlorophyll data
Chlorophyll is a measure of phytoplankton (microscopic algae) abundance in the water column. It is
analysed on water samples collected at the same time as samples for the nutrient parameters, and
expressed as a concentration in micrograms per litre. Chlorophyll is one part of the overall assessment
of phytoplankton status for WFD purposes, but can also be considered on its own as an indicator of
eutrophic impact.
As for the nutrient parameters above, data are from the EA WIMS archive from 2010-2014. WFD class
and confidence are taken from the nationally reported WFD classification results. The good/moderate
boundary value is the concentration above which the lake would be in moderate status for the WFD –
this is specific to each lake.
Other responses
The table shows the results of WFD classification for phytoplankton (free-floating microscopic algae),
macrophytes (aquatic plants) and diatoms (microscopic algae growing attached to the lake bed or on
submerged plants). Not all elements are available for all lakes.
EQR is the Ecological Quality Ratio, the basic measure used in WFD assessment to compare observed
with expected, or reference, conditions. This is then translated into a status class according to the
boundary values set for each biological element. Moderate, Poor or Bad status is indicative of impacted
conditions.
Number of years when algal blooms were observed based on reactive monitoring – this information is
taken from the EA’s Biosys data archive. Algal blooms are not routinely monitored but may be recorded
on the system when samples have been taken in response to reported blooms (”reactive monitoring”).
An absence of recorded blooms does not necessarily mean that no blooms have occurred. In some cases
the figure in this table may be zero, but other reports may be known of and referred to in the text
supplied by local Area staff.
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Text below the table is the response from local EA staff to the consultation questionnaire.
Palaeolimnology: For some lakes evidence is available from analysis of diatom remains in sediment
cores to show whether a substantial change in biological community has occurred over time, linked to
nutrient enrichment. This information is included here as a summary statistic, the square chord
distance, which can take values of 0 – 2.0, with anything over 0.48 representing a significant change.
Evidence of impact on aquatic features, and local assessment of eutrophic disturbance - text here is the
response of local EA staff to the consultation questionnaire
Review of Evidence and Recommendations
WFD Weight of Evidence for eutrophication: This section reports the weight of evidence for
eutrophication assessed in a structured manner for WFD purposes. The weight of evidence based on the
core WFD tools is a synthesis of the classification information presented in the previous sections. The
overall weight of evidence includes additional information relating to evidence of eutrophication (see
the eutrophication method document for further details), which may result in a change in the reported
certainty of a eutrophication impact.
Overall WFD status is the final class reported for WFD – for lakes this is based primarily on
eutrophication related elements, since nutrient pressure is considered the main threat to lakes in
England, but in some cases elements responding to other pressures may be included in this assessment.
Confidence in WFD status: This is the reported confidence that the WFD status is moderate or worse – a
statistical confidence from the classification tools is converted to “very certain”, “quite certain” or
“uncertain” (representing over 95%, 75-95% and less than 75% confidence respectively).
Current assessment of weight of evidence supporting designation: this section records the principal
comments of the national expert panels and a summary of the local EA Area view of the evidence.
Final summary (2017)
This section draws together and summarises the evidence from the preceding sections supporting the
proposed designation.
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Commonly used abbreviations and acronyms
DrWPA
Drinking water protected area (defined under the Water Framework Directive)
DWF
Dry weather flow (of sewage treatment works)
DWPP
Diffuse Water Pollution Plan
Biosys
The Environment Agency’s biological data recording system
CWS
County Wildlife Site
DO
Dissolved oxygen
EA Area
Environment Agency Operational Area (as at 2016)
EQR
Ecological quality ratio
ha
Hectares
kg N/yr
kilograms of nitrogen per year
LNR
Local nature reserve
m
metres
m3/d
cubic metres per day (volume of water abstracted or discharged, 1 cubic metre = 1000
litres)
mg/l
milligrams per litre, measure of concentration [may also be written as mg l-1]
µg/l
micrograms per litre [may also be written as µg l-1]
µeq/l
microequivalents per litre, measure of alkalinity
Ml/d
megalitres per day (i.e. millions of litres)
NEAP-N
National Environment and Agricultural Pollution – Nitrate model
NNR
National Nature Reserve
pH
measure of acidity, less than 7 = acid, more than 7 = alkaline
PWS
Public water supply
Ramsar
Designation of wetland of international importance under the Ramsar Convention
SAC
Special Area of Conservation (EU Habitats Directive)
SA(e)
Sensitive Area (eutrophic) designated under Urban Waste Water Treatment Directive
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SgZ
Safeguard Zone for Drinking Water Protected Areas ‘at risk’ of not meeting WFD
drinking water objectives.
SPZ
Source Protection Zone for areas of groundwater with particular sensitivity to pollution,
used to protect drinking water supplies.
SPA
Special Protection Area (EU Birds Directive)
SSSI
Site of special scientific interest, a national conservation designation
STW
Sewage treatment works
TON
Total oxidised nitrogen (i.e. nitrate plus nitrite)
TN
Total nitrogen
TP
Total phosphorus
UWWTD
Urban Waste Water Treatment Directive
WFD
Water Framework Directive
WIMS
Water Information Management System – the Environment Agency water quality data
archiving system
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