DATASHEET:
Nitrate vulnerable zone (NVZ)
designation 2017 – Eutrophic
Waters (Estuaries and Coastal
Waters)
Publication Date: June 2016
NVZ Name: Hamble Estuary
NVZ ID: ET3
Report for existing Polluted Water
Estuary
Hamble
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.environmentagency.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.environmentagency.gov.uk/wiyby/141443.aspx).
Page 2
Report for existing Polluted Water
Hamble Estuary
Ref. Code: ET3
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):
1)
England
England &
Wales
Wales
England &
Scotland
Name of regulator
Environment Agency, Solent & South Downs Area
2)
Designated Site name
Hamble Estuary
3)
Main river catchment
River Hamble
(There are also several smaller, direct rivers including Shawfords Lake. The Hamble is
strongly influenced by indirect rivers such as the Test and Itchen that flow into the top of
Southampton Water. The NVZ designation relates to the rivers Hamble, Test and Itchen).
4)
Location & extent of Designated Site
Hamble Estuary draining into Southampton Water- see Figure 1
5)
Type(s) of water body
Running freshwater
Still freshwater
Y
Estuarine water
Coastal water
Form A (cover sheet)
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Report for existing Polluted Water
6)
Hamble Estuary
In previous reviews this site was designated as a:
Y
Sensitive Area (Eutrophic)
Y
Polluted Water (Eutrophic)
Sensitive Area (Nitrate)
7)
Summary of qualifying sewage treatment work (STW) discharges (ie greater than
p.e. 10,000) which contribute to the pollution of the sensitive area.
Candidate name: Hamble Estuary
Name of discharge
Direct /
Indirect
NGR
Population
equivalent
Current Treatment
if TER
Level
enter Type
(PRIM,
SEC, TER) (N, P, NP)
Bishops Waltham
Indirect
SU5451 1687
13,655
TER
N&P
Millbrook
Indirect
SU 3817 1176
133,082
TER
N
Slowhill Copse
Indirect
SU 3862 1135
74,015
TER
N
Portswood
Indirect
SU 4362 1484
72,694
SEC
Woolston
Indirect
SU 4333 1034
63,457
Ashlett Creek
Indirect
SU 4800 0349
Total PE
14,338
SEC
Planned
Type of
TER
(N, P, NP)
N
(delayed)
SEC
371,242
Note: The Hamble also receives sewage effluent from other STWs which are too small, or contribute too
little, to qualify under the UWWTD e.g. the Hamble received sewage effluent directly from Bursledon STW
(too small to qualify under UWWTD) which transferred to Peel Common STW in 2014.
8)
Executive summary of evidence of change in eutrophic status since designation:
The Hamble Estuary has dual designation as both a Sensitive Area (Eutrophic) and a Polluted Water
(Eutrophic). It was designated as a Sensitive Area in 2007 under the Urban Waste Water Treatment
Directive (UWWTD). As a result it was recommended to tighten the consents of Bishops Waltham, Millbrook,
Slowhill and Woolston sewage treatment works (STWs). Southern Water completed these improvements to
STWs in 2014/2015, except for Woolston which has been delayed. Further reductions in nitrogen from
Habitats Directive requirements were delivered including the transfer of the discharge from Bursledon to Peel
common in the Solent in 2014. The Hamble Estuary was designated as Polluted Water (Eutrophic) under the
Nitrates Directive in 2008, with a Nitrate Vulnerable Zone (NVZ) established in its catchment and those of the
Test and Itchen.
At the time of the designations there was clear evidence that Hamble Estuary was eutrophic, based on the
widespread growth of the opportunistic macroalgae Enteromorpha spp. and Ulva spp. Macroalgal surveys
undertaken in 2003, indicated that macroalgae covered 78 ha of the intertidal area, exceeding the 25% of the
intertidal area UWWTD criteria.
This review focuses on nutrients and macroalgae because other potential indicators such as phytoplankton
blooms have never been an issue in the Hamble (summary information is presented to confirm this).
Form A (cover sheet)
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Report for existing Polluted Water
Hamble Estuary
Evidence from more recent studies show that nitrogen in the Hamble Estuary remains elevated with
concentrations exceeding the standards used to assess UWWTD compliance. Macroalgae surveys
undertaken in the summer of 2008, 2010 and 2013 indicate that macroalgae cover between 38% and 59% of
the available intertidal area. These levels of cover exceed the UWWTD criteria. The average summer
biomass of macroalgae is generally between 500 to 1150g/m 2 and entrained algae is present in some areas.
There is therefore clear evidence that there remains a eutrophication problem in the Hamble Estuary.
However, macroalgae does not regularily persists throughout the winter; when it is present, it is at extremely
low biomass of 70g/m2.
The recent nutrient budget for the Hamble Estuary shows that diffuse agricultural riverine sources of nitrogen
from all freshwater catchments are approximately 65% of all nitrogen sources. The modelling supports the
existing Polluted Water designation in that nitrogen from agricultural sources is a substantial
contribution to the nitrogen inputs into the Hamble Estuary.
Current measures to reduce nitrogen into the Hamble Estuary from agricultural and sewage sources
include a mixture of statutory and voluntary measures. Statutory measures include nutrient stripping at
several sewage works and a transfer of a discharge to the Solent, plus mandatory agricultural practice rules
in the NVZ known as the Action Programme Measures. Voluntary measures derive from advice and
incentives to farmers and landowners and include Catchment Sensitive Farming projects, Environmental
Stewardship Schemes and other measures detailed in the Test and Itchen and Solent Diffuse Water
Pollution Plans.
Nutrient control measures should not be removed as the process of nutrient / eutrophication reduction in
the Hamble Estuary will take a long time for a variety of reasons including the strong/considerable influence
of groundwater (in which nitrogen will decline very slowly), the relatively recent and/or ongoing
implementation of measures, the variety of sources, natural biological time lag and natural inter-annual
variation.
A steady concerted effort to reduce different nutrient sources to the Hamble Estuary is ongoing and this
should not be interrupted or stopped.
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 A (cover sheet)
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Report for existing Polluted Water
Hamble Estuary
Ref. Code: ET3
EC Urban Waste Water Treatment and Nitrates Directives
Form D: Estuarine Waters – Information, data, evidence
Existing Sensitive Area (Eutrophic) / Polluted Waters (Eutrophic)
1)
Designated Site name: Hamble Estuary
2)
Define approximate area of estuarine water using grid references:
(take name from Form A)
The PW(E) designation covers the whole of the Hamble Estuary (see Fig 1).
Start point
NGR 1: 452047, 111772
NGR 2: 452254, 111624
End point
NGR 3: 448439, 105680
NGR 4: 448676, 105177
Tributary 1
NGR 5: 451663, 112837
NGR 6: 452047, 111772
Tributary 2
NGR 7: 452846, 111831
NGR 8: 452254, 111624
Surface area (ha):
3)
223 ha
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 Figures 1 & 2
4)
Approximate retention/flushing time (days): a few days
5)
Brief description of geo-morphological nature of the estuary
The Hamble Estuary is one of three estuaries that discharge into Southampton Water, which in turn
discharges to the Solent .The Hamble Estuary joins Southampton Water towards its mouth on the eastern
bank; the other two estuaries, the Test and Itchen, discharge to the top of Southampton Water.
The Hamble Estuary is approximately 9 km long from the top of the tidal reach at Botley, to Southampton
Water. The estuary’s main river, the River Hamble, flows into the top of the estuary providing over two thirds
of the direct freshwater nitrogen load to the estuary. There are several other smaller streams that flow to the
estuary, the largest of which is Shawfords Lake which provides approximately 10% of the direct freshwater
nitrogen load; other small streams contribute much less.
The estuary receives a significant groundwater contribution from the rivers Hamble, Test and Itchen
catchments all of which have significant baseflow from Chalk groundwater originating from the East Hants
Chalk, the Test Chalk and the Itchen Chalk groundwater bodies. All three groundwater bodies are currently
at poor status for groundwater quality due to rising trends in nitrate. Because of the time it takes for nitrate to
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
travel to the water table it may take many years to see the results of measures to reduce nitrate loading in
these catchments.
6)
Summary of main uses and designations:
Y
Amenity
Y
Boating
Y
Water sports
Y
OSPAR problem area
EC Bathing Water
Y
Angling
Y
Commercial fishery
Y
Y
Designated EC Shellfish Harvesting
Area
Designated EC Shellfish Water
(bottom of estuary only)
Non - designated shellfish harvesting
area
Other uses or designations:
1.
7)
If waterbody has conservation status provide details





SOLENT MARITIME Special Area of Conservation (SAC)(EC Habitats Directive)
SOLENT & SOUTHAMPTON WATER Special Protection Area (SPA)(EC Birds Directive)
SOLENT AND SOUTHAMPTON WATER Ramsar (wetland of international importance designated
under the Ramsar Convention)
UPPER HAMBLE ESTUARY AND WOODS Site of Special Scientific Interest (Wildlife and
Countryside Act 1981, as amended
LEE-ON-THE SOLENT TO ITCHEN ESTUARY Site of Special Scientific Interest (Wildlife and
Countryside Act 1981, as amended).
The site comprises extensive intertidal muds supporting high densities of benthic invertebrates and
extensive beds of eelgrasses on the lower shore. It has a littoral fringe of vegetated shingle, saltmarsh,
and reedbed supporting an outstanding assemblage of nationally scarce coastal plants. The site
supports large numbers of overwintering wildfowl and waders which form an important component of the
internationally important bird populations of The Solent.
Natural England advises that eutrophication, due to elevated nitrogen, is a recognised threat to the
condition of the designated sites, particularly through increased macroalgal abundance.
The SPA is a Protected Area under the EC Water Framework Directive and Marine Protected Areas
(MPA) under the EC Marine Strategy Framework Directive. 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 sites and features.
8)
What chemical data are available?
Y
Dissolved available inorganic phosphorus (DAIP)
Y
Dissolved available inorganic nitrogen (DAIN)
Y
Chlorophyll-a
Cell counts
Dissolved Oxygen
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
9) What biological / observational data are available?
Angiosperms
Y
Planktonic algal blooms
Y
Macroalgae
Presence of foam / scum
Shellfish / invertebrate / fish mortality
Photographs
For the Water Framework Directive, Hamble Estuary forms a subsection of the Southampton Water
waterbody. Therefore there is no Water Framework Directive classification for the Hamble Estuary. The
NVZs established in the Hamble, Test and Itchen catchments followed the Hamble Estuary’s designation as
a Polluted Water (Eutrophic) under the Nitrates Directive in 2008. The upper areas of these catchments were
already NVZs for Groundwater nitrate levels under a previous review.
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
Figure 1 Map showing the Hamble Estuary, Polluted Waters (Eutrophic), rivers and the locations of the STW discharges which have had
improvements under the UWWTD and Habitats Directive. The extent of the NVZ in the catchment is shown hatched in yellow.
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
Figure 2: The Hamble Estuary, showing water sampling points from both the marine and freshwater environment and biological sample point for over
wintering macroalgae.
Note: The Hamble Estuary receives effluent from several STWs, some of which are too small or contribute too little to qualify under the UWWTD. They are included
in all modelling work. The locations of nutrient sources from STWs and rivers included in the models are shown in the map in Appendix 1.
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
Nutrients
Nutrients have been monitored at three sites in the mid, lower and mouth of the Hamble Estuary as shown in
Figure 2. The top of the estuary is difficult to access so has not been sampled. Table 1 below summarises
DAIN (Dissolved Available Inorganic Nitrogen) and DAIP (Dissolved Available Inorganic Phosphorus) data to
2015 for each site in the estuary, showing annual average and winter average concentrations (where winter
is November to February).
Table 1: Summary of Chemical data for the Hamble Estuary
Annual Average
Data
Start
Year
Count
(DAIN)
Chloro
phyll
(ug/l)
DAIN
(mmol/m3)
DAIN
(mg/l)
DAIP
(mmol/m3)
DAIP
(mg/l)
Salinity
G0003730
RIVER HAMBLE AT
BURSLEDON BRIDGE
1990
379
3.326
61.624
0.863
2.046
0.063
27.170
G0003728
BADMAN CREEK
SAMPLING POINT
1993
137
2.311
43.086
0.603
1.114
0.035
30.123
G0003726
HAMBLE ESTUARY AT
FERRY SLIPWAY
1990
362
3.133
42.376
0.594
1.248
0.039
30.868
Data
Start
Year
Count
(DAIN)
Chloro
phyll
(ug/l)
DAIN
(mmol/m3)
Winter Average
DAIN
(mg/l)
DAIP
(mmol/m3)
DAIP
(mg/l)
G0003730
RIVER HAMBLE AT
BURSLEDON BRIDGE
1990
85
0.915
107.923
1.512
2.409
0.075
G0003728
BADMAN CREEK
SAMPLING POINT
1993
30
0.727
85.895
1.203
1.545
0.048
G0003726
HAMBLE ESTUARY AT
FERRY SLIPWAY
1990
79
0.939
82.401
1.154
1.966
0.061
Salinity
28.675
The data in Table 1 shows that in all sampling locations nutrients exceed the CSTT* standards used in
the UWWTD compliance: these state that ‘hypernutrification’ exists when winter values of nutrient
concentrations significantly exceed 12mmoles/m³ DAIN in the presence of at least 0.2mmoles/m³ DAIP’. The
relevant data are shown in red in Table 1 for both winter and annual averages.
*CSTT = Comprehensive Studies Task Team
Note: The Hamble Estuary has been shown by previous work to be nitrogen limited, so nitrogen is the key
nutrient of concern for macroalgal growth. In this report nitrogen is also referred to as DAIN and DIN
(Dissolved Inorganic Nitrogen) since this is the terminology used for nitrogen standards that relate to relevant
EU Directives. Because The Hamble Estuary is nitrogen limited, phosphorus data is only shown initially to
enable comparison with nutrient standards.
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
Seasonal variation in nutrients
Seasonal averages are shown in Figure 3. Winter salinities are lower than summer salinities indicating the
freshwater inputs are a greater influence in the winter months.
Winter DAIN concentrations are much higher than summer concentrations at all sites (Figure 3). The highest
concentrations occur at the site nearest the river (G0003730) which is more influenced by freshwater nutrient
inputs. The difference between summer and winter concentrations throughout the estuary is more
pronounced than in other nearby estuaries such as Portsmouth.
Seasonal Averages
1.600
35.000
1.400
30.000
1.200
1.000
DAIN Summer Mean
20.000
Salinity
concentration (mg/l)
25.000
DAIN Winter Mean
0.800
Salinity Summer Mean
Salinity Winter Mean
15.000
0.600
10.000
0.400
5.000
0.200
0.000
0.000
River ->
Figure 3: Winter and summer average DAIN in the Hamble Estuary from 1990 to 2015, with sampling
sites arranged from river to mouth (where G0003730 is nearest the river and G0003726 is nearest the
estuary mouth).
Not only are winter nutrients higher than summer nutrients, late winter nutrients give the best estimate of
nutrients that will be available in spring to support primary production. Mid summer concentrations
demonstrate if nutrients limit primary production in the summer.
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
Spatial variation in nutrients
Figure 4 shows a scatter plot of winter DAIN against salinity at all sites. Concentrations ranged from 17 to
361 mmoles/m 3 and salinity ranged from 7 to 34 ppt. Lower salinity samples generally had higher DAIN
values indicating the influence of freshwater nitrogen loads (although there are a few high salinity samples
with elevated DAIN results).
Winter DAIN vs Salinity
400
350
DAIN (mmol/m3)
300
250
200
150
100
50
0
0.000
5.000
10.000
15.000
20.000
25.000
30.000
35.000
40.000
Salinity
Figure 4 Scatter plot of winter DAIN vs salinity at all sites, data from 1990 to 2015 (where where winter
is November to February).
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
Figure 5 shows the winter DAIN data spatially on a map of the Hamble. This shows that winter nutrient
concentrations are lower towards the estuary mouth and higher near the top of the estuary where the river
enters. The DAIN concentrations reflect the salinity gradients and highlight the importance of the nutrients
from the river.
Figure 5 Average winter DAIN concentrations in the Hamble Estuary and the Rivers Hamble and
Shawfords Lake from 1990 to 2015 (except for Shawfords Lake when monitoring stopped in 2006)
Trends in riverine nutrients
DAIN data from 1990 is available for sampling points in the River Hamble (main inflowing river), Shawfords
Lake (smaller stream), River Test and River Itchen; the data is shown in Figures 6 to 9. The data suggests
that DAIN levels in the River Hamble have not changed much over the past 25 years although the highest
peaks have reduced in recent years. DAIN levels appear to have decreased in Shawfords Lake stream over
the 16 years for which data is available (1990 to 2006). DAIN concentrations are much higher in the main
River Hamble than in Shawfords Lake stream. In the rivers Test and Itchen DAIN concentrations have been
steadily rising over the last 25 years.
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
R HAMBLE AT DURLEY
12.0
10.0
DAIN (mg/l)
8.0
6.0
4.0
2.0
0.0
Figure 6: Trends in riverine DAIN at lowest sampling points in the River Hamble (1990 to 2015)
SHAWFORDS LAKE AT FAIRTHORNE MANOR
12.0
10.0
DAIN (mg/l)
8.0
6.0
4.0
2.0
0.0
Figure 7: Trends in riverine DAIN at lowest sampling points in Shawfords Lake (1990 to 2006)
Form D (information, data, evidence)
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Hamble Estuary
River Test at Testwood
12.0
10.0
DAIN (mg/l)
8.0
6.0
4.0
2.0
0.0
Figure 8: Trends in riverine DAIN at lowest sampling points in the River Test (1990 to 2015)
River Itchen at Gaters Mill
12.0
10.0
DAIN (mg/l)
8.0
6.0
4.0
2.0
0.0
Figure 9: Trends in riverine DAIN at lowest sampling points in the River Itchen (1990 to 2015)
Form D (information, data, evidence)
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Hamble Estuary
Trends in nutrients in the Hamble Estuary
Nitrogen levels in the the Hamble Estuary have not much changed over the last 25 years as shown in
Figures 10 to 12 below. Figure 10 shows Site G0003730 nearest the river while Figure 12 shows Site
G0003730 nearest the estuary mouth; these two sites have 25 years worth of data. Figure 11 shows the
middle site, Site G0003728 at Badman Creek; unfortunately there is only data from1993/4 and 2007-2015 at
this site.
Figures 10 and 12 suggest that DAIN concentrations in the Hamble Estuary have not changed much over
the last 25 years, although there is some evidence that the highest peaks have reduced in more recent
years. Figure 11 also suggests little change in concentrations, although this data is less suitable for temporal
trend analysis.
Form D (information, data, evidence)
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Hamble Estuary
G0003730 - River Hamble at Burseldon Bridge
6.0
5.0
Figure 10
DAIN (mg/l)
4.0
3.0
2.0
1.0
0.0
G0003728- Badman Creek
6.0
5.0
Figure 11
DAIN (mg/l)
4.0
3.0
2.0
1.0
0.0
G0003726 - Hamble Estuary at Ferry Slipway
6.0
5.0
Figure 12
DAIN (mg/l)
4.0
3.0
2.0
1.0
0.0
Figures 10,11,12: DAIN concentrations in three sites in the Hamble Estuary to 2015
Form D (information, data, evidence)
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Report for existing Polluted Water
Hamble Estuary
The estuarine DAIN data have been analysed prior to and following the NVZ designation in 2008, to see if
there is any evidence of decreased nutrients following the designation. Table 2 shows the data prior to NVZ
designation (up to 2007) and following NVZ designation (2009 to present). Figure 13 presents the pre & post
NVZ designation data spatially on a map of the harbour.
Table 2 Winter DAIN data pre & post NVZ designation in 2008
Winter Average
DAIN (mg/l)
G0003730
G0003728
G0003726
HAMBLE ESTUARY AT BURSELDON BRIDGE
BADMAN CREEK SAMPLING POINT
HAMBLE ESTUARY AT FERRY SLIPWAY
Winter Average
DAIN (mmol/m3)
1994-2007
2009-2015
1994-2007
2009-2015
1.514
1.315
1.110
1.470
1.207
0.944
108.092
93.886
79.260
104.974
86.173
67.384
Data in red shows it exceeds the CSTT winter DAIN standard of 12 mmol/m³
Figure 13 Mean winter DAIN concentration before and after NVZ designation in 2008
The data show a slight decrease in DAIN in the estuary in the 7 years following NVZ designation in 2008.
The data also shows clearly that the Hamble Estuary remains subject to substantially elevated nutrients in
the period following designation as an NVZ. (There is insufficient data following recent nutrient stripping at
several STW discharges in 2014/15 to assess any changes from this).
Overall, all the data confirms that the Hamble Estuary remains hypernutrified (high in
nutrients) throughout the period. Estuarine nitrogen concentrations have not changed
much over the last 25 years. However there have been varying nutrient trends in the rivers
that influence the Hamble Estuary. In the main direct river, the River Hamble, there are no
clear signs of a reduction in nitrogen over the last 25 years, but in Shawfords Lake stream
there is a reduction in nitrogen over 16 years (although this is a small contribution to loads
Form D (information, data, evidence)
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Hamble Estuary
in the estuary). In the rivers Test and Itchen nitrogen concentrations have been steadily
rising over the last 25 years.
9)
Interpretation and discussion of biological evidence:
Chlorophyll data and Phytoplankton status
The Hamble Estuary does not exhibit high chlorophyll concentrations or significant phytoplankton blooms. Its
status as an SA(E) and PW(E) relates only to macroalgal growth.
Previous reviews for the UWWTD and Nitrates Directive concluded that there was no evidence of blooms of
unusual scale or duration and that chlorophyll concentrations are generally within a salinity-based chlorophyll
standard within the estuary.
The annual average chlorophyll concentrations shown in Table 1 demonstrate the low chlorophyll
concentrations found in the Hamble Estuary.
Macroalgae
Previous studies of opportunistic macroalgae in Hamble Estuary in the 2000’s reached the conclusion that
the Hamble Estuary should be designated as a Sensitive Area in 2007 and a Polluted Water in 2008.
Macroalgae surveys with aerial photography taken in 2003, concluded that denser macroalgae (25 to 100%)
covered 78 ha of the intertidal area, exceeding the 25% of the intertidal area UWWTD criteria. This resulted
in the recommendation of consent conditions for Nitrogen for several STW discharges. These were delivered
in 2014/2015 apart from Woolston STW where improvements have been delayed until 2019.
In the 2005 Habitats Directive Review of Consents the macroalgae mats in the Solent and Southampton
Water SPA were considered to have an adverse effect on the designated features. This resulted in the
recommendation that nitrogen standards should be further tightened and that the small (UWWTD non
qualifying) Bursledon discharge should be transferred to Peel Common STW and discharge into the Solent.
More recently macroalgae in the Hamble Estuary has been assessed as part of Southampton Water under
the WFD. The WFD classification method uses data on percent cover, biomass and the presence of
entrained algae. Macroalgae surveys in the Hamble were undertaken in 2008, 2010 and 2013 using remote
sensing methods based on aerial imagery. Interpretation of the aerial images concluded that between 46 and
72 ha of intertidal area was covered in macroalgae (density 25 to 100%). This represents between 38 and 59
% of the available intertidal area. The Hamble Estuary exceeds the UWWTD criteria in all of the three years.
There is no Water Framework Directive (WFD) classification for the Hamble Estuary as it is a sub section of
Southampton Water WFD waterbody. However the three surveys undertaken in 2008, 2010 and 2013 would
only achieve MODERATE WFD status (yearly EQR* scores of 0.63 and 0.48 and 0.58 respectively). The
Hamble Estuary on its own exceeds the WFD criteria for opportunistic macroalgae in two out of the three
years.
Trends in macroalgae
The variability in the extent of macroalgae in the Hamble Estuary since 2003 is show in Figure 14. It shows
the extent of macroalgae (25 to 100% cover) in the Hamble has ranged between 46 and 78 Ha. The smallest
extent was recorded in 2008 and 2013 the greatest extent was recorded in 2003 and 2010. No clear trends
can be detected since the NVZ designation in 2008.
Form D (information, data, evidence)
Page 20
Report for existing Polluted Water
Hamble Estuary
Hamble - Extent of macroalgae overall and in each density class
100
90
80
Area (Ha)
70
60
50
75-100% Cover
40
50-75% Cover
30
25-50% Cover
20
10
0
2003
2008
2010
2013
Year
Figure 14: Extent of macroalgae in the Hamble Estuary (summer 2003 to 2013)
*EQR: The WFD classification is reported as an Ecological Quality Ratio (EQR). The EQR value ranges from zero to
one. An EQR with a value of one represents reference conditions and a value of zero represents a severe impact.
Over wintering macroalgae
Seasonal macroalgal biomass surveys have also been undertaken at two fixed sites in the Hamble Estuary
(location of sites is shown in Figure 2) to assess how biomass varies over the year and if macroalgae
persists through the winter.
Hamble Estuary
5000
4500
4000
3500
Wet weight (g/m2)
3000
2500
2000
1500
1000
500
Hamble River SC
May-06
Mar-06
Jan-06
Nov-05
Sep-05
Jul-05
May-05
Mar-05
Jan-05
Nov-04
Sep-04
Jul-04
May-04
0
Brooks Avenue
Figure 15: Macroalgal seasonal biomass at Hamble River SC and Brooks Avenue in the
Hamble Estuary (May 2004 to May 2006)
Form D (information, data, evidence)
Page 21
Report for existing Polluted Water
Hamble Estuary
The results in Figure 15 show that peak biomass varies between May to September and declines late in the
winter between January and March. Macroalgae survived the winter months of January to March in 2005 but
not in 2006. These sites have a substantial quantity of macroalgae in the summer months but only persist
through the winter in some years and biomass in the winter is extremely low - less than 70g/m2.
The primary symptom of eutrophication in Hamble Estuary is the development of extensive mats of green
macroalgae, primarily Enteromorpha spp. and Ulva spp., in intertidal areas throughout the harbour in the
summer. Macroalgae surveys in 2008, 2010 and 2013 indicate that macroalgae cover between 38% and
59% of the available intertidal area. The average summer biomass of macroalgae for the whole of the
harbour is generally between 503 and 1156g/m2 and entrained algae is present in a small area. However
macroalgae does not regularily persists throughout the winter and, when present, is only at extremly low
biomass of less than 70g/m2.
In summary, the biological evidence clearly indicates that macroalgae is still a problem in
the Hamble Estuary based on the combination of percentage cover, biomass, the presence
of entrained algae but that it does not regularly persist through the winter.
10)
Which of the methodology indicators are exceeded?
Y
Nitrate concentrations (February nitrogen concentrations significantly enhanced)
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 )
Y
11)
Macroalgae exceeds thresholds (UWWT and WFD)
Other evidence of adverse effects on uses and designations:
If overwintering macroalgae is present at the same time as important overwintering birds (for which the site is
designated under the Habitats Directive), the macroalgae may interfere with feeding patterns and prey
distribution. However macroalgae is only present in some winters and at very low biomass in the Hamble
Estuary.
If present, entrained macroalgae and overwintering macroalgae reduces the time and opportunity for the
mudflats to recover from its adverse effects. Small areas of entrained macroalgae are present in the Hamble
Estuary.
Form D (information, data, evidence)
Page 22
Report for existing Polluted Water
12)
Hamble Estuary
List the current WFD status/potential for any WFD waterbodies within the SA(E)/PW(E)
Waterbody
ID
Waterbody
Name
Current
overall
status
2015
Ecological
status
Status of biological elements sensitive to Status of Phys-chem
nutrient enrichment 2015
supporting elements
2015
2015
Phytoplankton
Macroalgae
Angiosperms
Dissolved
Inorganic
Nitrogen
Dissolved
Oxygen
The Hamble
Estuary is not a
WFD waterbody.
(No classification)
Based on the Environment Agency’s latest (December 2015) weight-of-evidence assessment for certainty of eutrophication, the Hamble Estuary currently comes out
as “Quite Certain of a eutrophication problem”. Further details of the weight-of-evidence approach are set out in the method statement for waters subject to
eutrophication (Defra, 2016).
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?
The Hamble Estuary is a small sub-section of the much larger Southampton Water waterbody. The Southampton Water transitional waterbody is failing the DIN
standard. It is consistently at MODERATE status.
There is a significant groundwater contribution from the Hamble, Test and Itchen catchments all of which have significant baseflow from Chalk groundwater
originating from the East Hants Chalk, the Test Chalk and the Itchen Chalk groundwater bodies. All three groundwater bodies are currently at poor status for
groundwater quality due to rising trends in nitrate and have failed both the General Chemical test and the Drinking Water Protected area test for nitrate.
Due to the time it takes for nitrate to travel to the water table it may take many years to see the results of measures to reduce nitrate loading in these catchments.
Form D (information, data, evidence)
Page 23
Report for existing Polluted Water
14)
Executive summary of the chemical,
eutrophication in the SA(E)/PW(E)
Hamble Estuary
biological and other
evidence illustrating
Winter DAIN levels exceed the criteria used in the UWWTD and indicate that the Hamble Estuary is
hypernutrified throughout. Concentrations of DAIN in River Hamble have remained similar over the last 25
years but concentrations in the Rivers Test and Itchen have been rising. In Shawfords Lake stream DAIN
concentrations appear to have decreased.
The primary symptom of eutrophication in the Hamble Estuary is the development of extensive mats of green
macroalgae, primarily Enteromorpha spp. and Ulva spp., in intertidal areas in the summer. Macroalgae
surveys in 2008, 2010 and 2013 indicate that macroalgae cover between 38% and 59% of the available
intertidal area. The average summer biomass of macroalgae generally between 500 to 1150g/m 2 and
entrained algae is present in some areas. However, macroalgae does not regularily persists throughout the
winter; when it is present it is at extremely low biomass of 70g/m 2.
There is therefore clear evidence that there remains a eutrophication problem in the Hamble Estuary.
15)
Summary of eutrophication control measures (already in progress and/or already
planned) if any, for the existing area.
Statutory measures
The Hamble Estuary was designated a Sensitive Area in 2007 under the Urban Waste Water Treatment
Directive. As a result it was recommended to tighten the consents of Bishops Waltham, Millbrook, Slowhill
and Woolston STWs. Southern Water completed these improvements to STWs in 2014/2015, except for
Woolston which has been delayed. Further reductions in nitrogen from Habitats Directive requirements were
delivered including the transfer of the discharge from Bursledon to Peel Common in the Solent in 2014.
The Hamble Estuary was designated a Polluted Water (Eutrophic) under the Nitrates Directive in 2008, with
a Nitrate Vulnerable Zone (NVZ) established in its catchment and those of the Rivers Test and Itchen (see
Figure 1). 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.
Voluntary measures
There are also additional voluntary measures within the catchments affecting the Hamble Estuary. These
measures derive from advice and incentives to farmers and landowners to reduce nutrient inputs to water,
and include:



Catchment Sensitive Farming (CSF) projects
Environmental Stewardship Schemes
Test and Itchen Diffuse Water Pollution Plan. Solent Diffuse Water Pollution Plan which
relates to several catchments that border the Eastern Solent and the Isle of Wight.
Form D (information, data, evidence)
Page 24
Report for existing Polluted Water
Hamble Estuary
Ref. Code: ET3
EC Urban Waste Water Treatment and Nitrates Directives
Form G: Effects of Nutrient Reduction
Existing Sensitive Area (Eutrophic) / Polluted Waters (Eutrophic)
1)
Designated Site name: Hamble Estuary
2)
Type(s) of water body:
(take name from Form A)
(take info from Form A)
Running freshwater
Still freshwater
Y
Estuarine water
Coastal water
3)
Summary of qualifying sewage treatment work discharges (ie greater than p.e. 10,000)
which contribute to the pollution of the sensitive area
(copy info from Form A)
Candidate name: Hamble
Name of qualifying
discharge
Estuary
Direct/Indirect
Population
Equivalent
NGR
Current level of treatment
(>10,000 PE)
Bishops Waltham
Indirect
SU5451 1687
13,655
TERTIARY
Millbrook
Indirect
SU 3817 1176
133,082
TERTIARY
Slowhill Copse
Indirect
SU 3862 1135
74,015
TERTIARY
Portswood
Indirect
SU 4362 1484
72,694
SECONDARY
Woolston
Indirect
SU 4333 1034
63,457
SECONDARY
Ashlett Creek
Indirect
SU 4800 0349
14,338
SECONDARY
Total PE
371,242
Remarks: In addition, following the Habitats Directive Review of Consents, the discharge from Bursledon
STW was transferred to Peel Common STW to be discharged into the central Solent.
Note: Hamble Estuary also receives sewage effluent from some STWs that are too small, or contribute too little, to qualify
under the UWWTD, but they are included in all the modelling work as discussed in section 5 below. They include:

Small STWs including Bursledon and those in freshwater rivers

Large marine STWs discharging outside the estuary, offshore (with water exchange at the estuary entrance)
The locations of these other nutrient sources from STWs and rivers included in the model are show in the map in the
Appendix.
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 predesignation.
N/A
Form G (effects of enhanced treatment)
Page 25
Report for existing Polluted Water
5)
Hamble Estuary
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.
Annual nitrogen contributions to the Hamble Estuary were calculated. The contributions were calculated
without the transfer of the STW discharge at Bursledon (transferred in 2014), but taking into account the
nutrient reductions at the STW which have taken place (e.g. Bishops Waltham, Millbrook and Slowhill
STWs). They also included the reduced nitrogen contribution from Woolston STW which has not yet come on
line as improvements at Woolston STW are delayed until 2019. The nitrogen contributions are shown in
Figure 16 (which is colour coded to show contributions from marine sources in blue, riverine sources in
greens and sewage sources in reds).
% of N to Hamble
Offshore other (<1% each) = 3%
Bishops Waltham STW = 8%
Offshore Soton Water STWs = 3%
Offshore Christchurch Rivers = 3%
Bursledon STW = 6%
Offshore River Itchen = 5%
Bishops Waltham STW = 8%
Bursledon STW = 6%
Offshore River Test = 10%
Hamble Diffuse = 37%
Hamble Urban Diffuse = 2%
Shawford Lake = 7%
Curbridge Streams = 4%
Hook Lake = 3%
Hedge End Streams = 1%
Offshore Coastal background = 13%
Offshore River Test = 10%
Offshore Coastal background = 13%
Offshore River Itchen = 5%
Offshore Christchurch Rivers = 3%
Offshore Soton Water STWs = 3%
Offshore other (<1% each) = 3%
Hamble Diffuse = 37%
Hedge End Streams = 1%
Hook Lake = 3%
Curbridge Streams = 4%
Shawford Lake = 7%
Hamble Urban Diffuse = 2%
Notes:


The map in the Appendix should be viewed in association with this source apportionment information
as it shows the location of the rivers and point sources refered to.
This data is derived from model outputs from CPM, SAGIS and Telemac models.
Figure 16: Relative contribution of all nitrogen sources combined within the Hamble Estuary
Available evidence from recent modelling work indicates that approximately 68% of the nitrogen in the
Hamble Estuary is from freshwater diffuse sources (where diffuse agricultural sources from the River Hamble
catchment account for 49%). Only a small proportion is from offshore coastal background: 13%. All Sewage
treatment works across the area including those in Southampton Water and the freshwater catchments only
account for 17% of the nitrogen load. The percentage contribution from sewage treatment works will now
have reduced by 6% due to the transfer of the discharge from Bursledon to Peel Common in 2014.
The figures support the existing Polluted Water designation as the biggest nitrogen contribution
(65%) is from agricultural sources in the Hamble, Test, Itchen and other catchments.
Form G (effects of enhanced treatment)
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Report for existing Polluted Water
Hamble Estuary
Summarise how this has changed over time.
Trends in freshwater sources
Trends in nitrogen concentrations in freshwater sources to the Hamble Estuary are shown in Figure 17.
DAIN levels in the River Hamble have not changed much since the 1990’s. Concentrations in the much
smaller Shawfords Lake stream were much lower than in the River Hamble and showed a decrease in
nitrogen prior to 2007, when monitoring stopped (prior to the NVZ designation).
DAIN concentrations in the Rivers Test and Itchen are of similar magnitude to the Hamble and have been
rising steadily over the 25 year period for which data were retrieved (Figure 18 and 19).
There has been no decrease in concentrations of DAIN in the major rivers (Hamble, Test and Itchen)
following the 2008 NVZ designation in the catchments; conversely DAIN has been increasing in the Rivers
Test and Itchen. This will be partly due to the strong influence of groundwater in these catchments: nitrate in
groundwater takes a long time to travel to the water table so consequently will take years to see the results
of measures to reduce nitrate loading in the catchment.
RIVER HAMBLE AT DURLEY AND SHAWFORDS LAKE
9.0
8.0
7.0
DAIN (mg/l)
6.0
5.0
4.0
3.0
2.0
1.0
0.0
R HAMBLE AT DURLEY
SHAWFORDS LAKE AT FAIRTHORNE MANOR
Figure 17: Trends in annual average DAIN in the River Hamble at Durley and Shawfords Lake stream,
(Monitoring in Shawfords Lake stopped in 2007).
Form G (effects of enhanced treatment)
Page 27
Report for existing Polluted Water
Hamble Estuary
River Test at Testwood
9.0
8.0
7.0
DAIN (mg/l)
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Figure 18: Trends in annual average DAIN in the River Test at Testwood monitoring point
River Itchen at Gaters Mill
9.0
8.0
7.0
DAIN (mg/l)
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Figure 19: Trends in annual average DAIN in the River Itchen at Gaiters Mill sampling point.
Form G (effects of enhanced treatment)
Page 28
Report for existing Polluted Water
Hamble Estuary
Trends in discharges
Nitrogen concentrations from Millbrook, and Slowhill Copse STW discharges have significantly reduced since
nitrogen removal was installed in the STWs (Figure 20). The greatest level of improvement was in 2014.
However, the major reconstruction of Woolston STW has been delayed and will not be completed until 2019,
so concentrations from Woolston remain around 30mg/l (annual average).
Bursledon STW located on the Hamble Estuary was too small to qualify for UWWTD criteria but was
transferred to Peel Common STW in the Solent in 2014 as result of the Habitats Directive Review of
consents.
45
40
Annual average DAIN (mg/l)
35
30
25
20
15
10
5
0
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Millbrook STW
Slowhill STW
Woolston STW
Figure 20: Annual average concentration of DAIN in STW final effluents from Millbrook, Slowhill and
Woolston STWs which discharge into Southampton Water
Finally, Bishops Waltham a small STW located upstream in the Freshwater catchment was targeted by the
Bishopsconcentrations
Waltham STW have remained below 15mgl since 2007 (Figure
UWWTD to deliver 15mg/l. Annual average
21), but have not changed substantially as concentrations from this small STW were not particularly high.
25
Annual average DAIN (mg/l)
20
15
10
5
0
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
Bishops Waltham STW
Figure 21: Annual average concentration of DAIN in STW final effluents from Bishops Waltham STW
located upstream in the River Hamble
Form G (effects of enhanced treatment)
Page 29
Report for existing Polluted Water
6)
Hamble Estuary
Give a summary of the eutrophication control measures (in progress and/or planned), for
the SA(E)/PW(E).
Statutory measures
The Hamble Estuary was designated an SA(E) in 2007. As a result it was recommended to tighten the
consents of Bishops Waltham, Millbrook, Slowhill Copse and Woolston STWs. Southern Water completed
these improvements to STWs in 2014/2015 with the exception of Woolston where the reconstruction of the
STW has been delayed until 2019. Further reductions in nitrogen from Habitats Directive requirements were
delivered in 2015 including the transfer of the Bursledon STW discharge located on the Hamble Estuary to
Peel Common STW.
The Hamble Estuary was designated a PW(E) in 2008 and the Hamble, Test and Itchen catchments have
been designated as an NVZ (see Figure 1). 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.
Voluntary measures
There are also additional voluntary measures within the catchments affecting the Hamble Estuary. These
measures derive from advice and incentives to farmers and landowners to reduce nutrient inputs to water,
and include:



7)
Catchment Sensitive Farming (CSF) projects
Environmental Stewardship Schemes
Test and Itchen Diffuse Water Pollution Plan; Solent Diffuse Water Pollution Plan which
relates to several catchments that border the Eastern Solent and the Isle of Wight.
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?
There is no evidence that the eutrophication status of Hamble Estuary has changed – it is still
eutrophic as shown by all the evidence above.
The process of nutrient/eutrophication reduction in the Hamble will take a long time for a variety of reasons
including the strong influence of groundwater in which nitrogen will decline very slowly. Agricultural diffuse
sources are significant and further reductions from this sector are anticipated as the uptake of statutory and
regulatory measures continues. Sewage discharges are a small nutrient source and many of the larger
sewage discharges have already been tackled via nutrient stripping and STW diversion schemes. The
coastal background source is anticipated to reduce very slowly over time, reflecting improvements in
agricultural diffuse and sewage sources throughout the Solent area.
Any changes as a result of nutrient reductions from agriculture or recent sewage inputs are likely to take a
long time for reasons including:







Nutrients will take a long time to decrease in groundwater
Uptake of some agricultural measures is ongoing
STW improvements delivered recently (e.g. Bursledon, Millbrook and Slowhill Copse in 2014/2015)
The changes in nutrient loadings are relatively small
There are a variety of nutrient sources
There is a biological time lag
There is inter-annual variation in natural factors like weather
Form G (effects of enhanced treatment)
Page 30
Report for existing Polluted Water
8)
Hamble Estuary
If control measures were removed, would the area be at risk of becoming eutrophic once
more?
Nutrient control measures should not be removed as the process of nutrient reduction in the Hamble
Estuary will take a long time as outlined above. A steady concerted effort to reduce different nutrient
sources to the harbour is ongoing and this should not be interrupted or stopped.
If nutrient control measures were removed the Hamble Estuary might never change its status as a eutrophic
water body.
Form G (effects of enhanced treatment)
Page 31
Report for existing Polluted Water
Hamble Estuary
Appendix
Figure 22: Locations of rivers and sewage treatment works (STW) used in the modelling to calculate the contribution of nitrogen of each source
into the harbours in the Solent area. Please note that all the small STWs in each of the freshwater catchments are included in the model, but may
not have been included on this map.
Appendix
Page 32
NVZ Name:
NVZ ID: