Appendix D Environmental Features Assessment

January 2018 Version: Final Draft for EA/NE Review

Contents

D1. Introduction ...... 4 D.1.1. Approach ...... 4 D.1.2. Proposed drought orders and extent of potential impact ...... 4 D.1.3. Structure of the Appendix ...... 5 D2. Designated sites ...... 8 D.2.1. European designated sites ...... 8 D.2.2. Special Areas of Conservation ...... 8 D.2.2.1.1. Baseline ...... 8 D.2.2.1.2. Features assessment ...... 10 D.2.3. Special Protection Areas ...... 25 D2.3.1 Solent and Southampton Water SPA ...... 25 D 2.3.2 Solent and Dorset Coast potential Special Protection Area (pSPA)26 D.2.4. Ramsar ...... 27 D.2.4.1 Solent and Southampton Water Ramsar Site ...... 27 D.2.5. Sites of Special Scientific Interest ...... 28 D.2.5.1.1. Baseline ...... 28 D.2.5.1.2. Assessment Methodology ...... 30 D.2.5.1.3. Features Assessment ...... 31 D3. Ecological community assessment and WFD assessment...... 42 D 3.3 Itchen Water body (GB107042022580) ...... 43 D.3.3.1. Macrophytes ...... 43 D.3.3.2. Diatoms ...... 46 D.3.3.3. Freshwater macroinvertebrates ...... 48 D.3.3.4. Freshwater fish ...... 53 D.3.2.4 Hydromorphological elements supporting the biological elements 57 D.3.2.5 Chemical and physico-chemical elements supporting the biological elements ...... 58 D.3.2.6 Specific pollutants ...... 58 D 3.3 Southampton Water transitional water body (GB520704202800) ...... 59 D.3.3.1 Macroinvertebrates ...... 59 D 3.3.2 Macroalgae ...... 60 D.3.3.3 Fish ...... 60 D4. NERC and notable species and habitats ...... 63

D.4.1. NERC species...... 63 D.4.2 NERC habitats ...... 63 D5. Non-native invasive species...... 63

D1. Introduction D.1.1. Approach This appendix presents information regarding the environmental effects associated with the Gaters Mill and Lower Itchen sources drought orders. Points of interest referred to throughout this appendix are indicated in Figure 1.

The approach of the assessment is to determine the magnitude and significance of additional impacts from implementation of the Gaters Mill and Lower Itchen sources drought orders over and above those occurring due to natural drought conditions. The potential effect on each sensitive receptor is assessed using the best available science and each assessment describes the analyses carried out along with a statement of the assessed impact in terms of the statutory test for the designated features.

The relevant statutory tests applied are as follows:

 Habitats Directive Council Directive 92/43/EEC, Birds Directive Council Directive 2009/147/EC and Ramsar Convention Sites – “likely significant effect” of the drought orders on the relevant site or feature – SPA,SAC or Ramsar in order to determine whether an appropriate assessment is required. If an appropriate assessment is undertaken, whether an adverse effect on the integrity of the site can be ruled out.  Wildlife and Countryside Act 1981 – whether the drought orders are “likely to damage” SSSI features.  Water Framework Directive Council Directive 2000/60/EC. The assessment of environmental features is informed by the assessment of the physical environment (which includes hydrology and hydrodynamics; geomorphology; and water quality), as presented in Appendix B of the EAR.

This assessment focuses in particular on potential impacts on the qualifying features of the River Itchen Special Area of Conservation (SAC) which have been extensively studied in the River Itchen Sustainability Study (RISS)1 and the subsequent Habitats Regulations Review of Consents (RoC) Stage 3 Appropriate Assessment2 and Stage 4 Site Action Plan3. In addition, the habitats and species that are notified in the citation for the River Itchen SSSI are considered in detail. Available Water Framework Directive (WFD) data are also discussed in relation to the scale at which discrete water body effects may occur. WFD analysis is explicitly linked back to the impact pathways discussed in relation to the SAC and Site of Special Scientific Interest (SSSI) qualifying features. D.1.2. Proposed drought orders and extent of potential impact The proposed drought orders are summarised below for context.

D.1.2.1. Drought orders on the Test and Itchen Southern Water has developed four drought orders on the River Test and River Itchen to help maintain public water supplies to the Western Area during drought conditions. It is proposed that these are operated in the following order to limit environmental impact:

 Testwood drought order;

1 Halcrow (2003). River Itchen Sustainability Study. Draft Strategy Document and Technical Appendices 2 Environment Agency (2005) River Itchen SAC. Habitats Regulations Review of Consents Stage 3 Appropriate Assessment. Environment Agency 3 Environment Agency (2007) River Itchen SAC Stage 4 Site Action Plan.

 Candover Augmentation Scheme drought order;  Gaters Mill drought order; then  Lower Itchen sources drought order. This environmental assessment is concerned with the impacts of the Gaters Mill and Lower Itchen sources drought orders. The drought order for the Portsmouth Water Gaters Mill source will be used in preference to that for Southern Water’s Lower Itchen sources with the view to limiting potential impact on the River Itchen. In practice, it is likely these drought orders would be applied for simultaneously, and as such have been assessed here in a cumulative fashion.

D.1.2.2. Proposed Gaters Mill drought order The drought order would comprise of:

 Temporarily relaxing the Hands-off-flow (HOF) abstraction licence condition from 194 Ml/d down to 150 Ml/d.  This would enable continued abstraction from Portsmouth Water’s Gaters Mill source, enabling continuation of the bulk treated water supply to Southern Water. D.1.2.3. Proposed Lower Itchen sources drought order The drought order would comprise of:

 Relaxing the Section 52 HOF abstraction licence condition from 198 Ml/d down to 160 Ml/d. This would enable continued abstraction from Southern Water’s Lower Itchen sources, which comprise of:

 Otterbourne, which includes: - Otterbourne surface water (SW) - Otterbourne groundwater (GW), which includes abstraction from Twyford Moors  Twyford GW

D.1.2.1. Extent of environmental assessment

Groundwater impact Appendix B of the EAR identified that only abstraction from the groundwater component of Southern Water’s Lower Itchen sources drought order has the potential to impact on the Chalk aquifer; the abstraction at Gaters Mill occurs in the furthest downstream reach of the River Itchen upstream of the tidal limit and this reach is hydraulically isolated from the underlying aquifer. The maximum groundwater impact will depend on the operational abstraction split between the surface water and groundwater sources of the Lower Itchen sources.

Surface water impact Surface water impacts in the River Itchen and surrounding wetlands may occur either directly as a result of surface water abstraction, or, in the area where the Chalk aquifer is unconfined, indirectly, through a reduction in baseflow due to the lowering of groundwater levels. D.1.3. Structure of the Appendix This appendix is set out in the following sections:

 Section D.2 Designated sites  Section D.3 Ecological community and WFD assessment  Section D.4 NERC and notable species and habitats  Section D.5 Non-native invasive species

Figure 1 Designated sites within the study area Based upon: the Ordnance Survey Map by Southern Water by permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office. Crown Copyright 1000019426

D2. Designated sites D.2.1. European designated sites The only European Site on the River Itchen and the primary consideration of this environmental assessment is the River Itchen SAC. The downstream Solent and Southampton Water Special Protection Area (SPA) and Ramsar sites are also considered although the drought orders will not affect the tidal regime or elicit significant impacts on salinity gradients that could trigger a significant impact pathway on either of these sites. D.2.2. Special Areas of Conservation D.2.2.1. River Itchen SAC D.2.2.1.1. Baseline

Reasons for designation The Annex I habitat which is the primary reason for designation is:

 Water courses of plain to montane levels with the Ranunculion fluitantis and Callitricho- Batrachion vegetation. The River Itchen is a classic example of a sub-type 1 chalk river. The river is dominated throughout by aquatic Ranunculus spp. The headwaters contain pond water-crowfoot Ranunculus peltatus, while two Ranunculus species occur further downstream: stream water-crowfoot R. penicillatus ssp. pseudofluitans, a species especially characteristic of calcium-rich rivers, and river water-crowfoot R. fluitans. Annex II species that are a primary reason for selection are:

 Southern damselfly Coenagrion mercuriale. Strong populations of southern damselfly occur. The River Itchen represents one of the major population centres in the UK. It also represents a population in a managed chalk-river flood plain, an unusual habitat for this species in the UK, rather than on heathland.  Bullhead Cottus gobio. The Itchen is a classic chalk river that supports high densities of bullhead throughout much of its length. The river provides good water quality, extensive beds of submerged plants that act as a refuge for the species, and coarse sediments that are vital for spawning and juvenile development. Annex II species that present as a qualifying feature, but not a primary reason for site selection are:

 White-clawed crayfish, Austropotamobius pallipes  Brook lamprey, Lampetra planeri;  Atlantic salmon, Salmo salar;  Otter, Lutra lutra.

River Itchen SAC Conservation objectives The Conservation Objectives are to ensure that the Conservation Status of the site is maintained or restored as appropriate, and ensure that the site contributes to achieving the Favourable Conservation Status of its Qualifying Features, by maintaining or restoring:

 The extent and distribution of qualifying natural habitats and habitats of qualifying species;  The structure and function (including typical species) of qualifying natural habitats;  The structure and function of the habitats of qualifying species;

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 The supporting processes on which qualifying natural habitats and the habitats of qualifying species rely;  The populations of qualifying species; and,  The distribution of qualifying species within the site.

Favourable condition flow targets for the River Itchen SAC and SSSI The Joint Nature Conservation Committee (JNCC) and the conservation agencies, including Natural England (NE), published revised CSMG (Common Standards Monitoring Guidance) in January 2014, for setting and monitoring objectives for all Sites of Special Scientific Interest (SSSI), including the Natura 2000 (N2K) Protected Areas4. The proposed flow targets are summarised in Table 1.

Table 1 Common standards monitoring guidance flow targets for rivers River size Q10 High flows) moderate flows) high flows) flows Headwater 5 10 15 15 River 10 15 20 10 Large river 15 20 20 20 Notes: Figures are percentage deviations from daily naturalised flow. Headwaters are rivers with mean annual flow <0.62 m3 s-1, rivers mean annual flow >0.62 m3s-1 to 40 m3s-1 and large rivers with mean annual flow >40 m3s-1. Flow targets for the River Itchen SAC, derived primarily from an evaluation of macroinvertebrate communities5, were developed as part of the Review of Consents (RoC) process. These flow targets, which underpin the River Itchen Sustainability Reductions, are summarised below in Table 2. The two SAC management units relevant to this assessment are Management Unit 5 (Easton gauging station to Allbrook & Highbridge gauging station) and Management Unit 6 (Allbrook & Highbridge gauging station to Riverside Park gauging station).

Table 2 River Itchen Stage 4 RoC invertebrate flow targets Stage 4 Invertebrate flow Management unit criteria (Ml/d) 1 2 3 4 5 6 1. Long-term summer Q95 26 92 25 241 262 257 must exceed: 2. Flow should not fall 20 69 19 182 198 194 below: 3. Summer Q95 should not 24 83 23 218 237 233 fall below: in more in more in more in more in more in more than 1:5 than 1:5 than 1:6 than 1:6 than 1:6 than 1:5 years years years years years years Notes: the two management units relevant to the assessment are highlighted in bold. For the River Itchen, rather than adopting the revised CSMG flow targets to replace the RoC flow targets, the Environment Agency and Natural England are working together to consider the evidence for adding the RoC target flow regime to the revised CSMG targets in an amalgamated form by 20216. Until 2021, Natural England and the Environment Agency are working with the interim targets

4 Joint Nature Conservation Committee (2014) Common Standards Monitoring Guidance for Rivers. 5 Exley, K (2005). River Itchen macroinvertebrate community relationship to river flow changes. Environment Agency Report. 6 Natural England and Environment Agency (2014) Moving towards common standards monitoring guidance targets for SAC rivers – the River Itchen.

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derived from the RoC Stage 4 Site Action Plan for the River Itchen SAC. The Environment Agency’s reasoning behind the use of interim targets is two-fold:

 Implementing the revised CSMG flow targets entails a period of technical work and discussing the implications with licence holders. To not implement the RoC decisions would leave the river exposed to risks in the meantime. So, implementing RoC decisions went ahead, but it does not preclude implementation of revised CSMG flow targets too;  Revised CSMG flow targets are more stringent at low, moderate and high flows than the Environment Agency’s RoC flow targets. However, the Environment Agency’s flow targets are more protective of the River Itchen than revised CSMG targets for very low flows, i.e. it has a HOF whereas revised CSMG flow targets allow for some abstraction at all flows7.

River Itchen SAC Conservation Status The overall Conservation Status at a UK level of “Water courses of the plain to montane levels of Ranunculion fluitantis and Callitricho-Batrachion vegetation” is ‘Bad’ with an improving trend. Conservation Status for SACs is not reported at a site level but the relevant site or feature condition of the underpinning SSSI is used as an indicator and is the basis for the condition reporting to Defra.

There are multiple Units of the River Itchen SSSI within the hydrological zone of influence of the drought order and these are considered in more detail in Section D.2.5.

D.2.2.1.2. Features assessment The RoC Appropriate Assessment for the River Itchen concluded that the water-sensitive habitats/species that could be adversely affected by abstraction were the macrophyte habitat and populations of southern damselfly, Atlantic salmon and white-clawed crayfish. Of these flow- sensitive habitats/species, the white-clawed crayfish is restricted to the Upper Itchen tributaries8 and populations would therefore not be affected by the proposed Lower Itchen drought orders, but the remaining three habitats/species could potentially be affected by a reduction in river flows.

Annex I habitat - water courses of plain to montane levels with Ranunculion fluitantis and Callitricho-Batrachion vegetation The macrophyte community is a key component of the Annex I habitat - water courses of plain to montane levels with Ranunculion fluitantis and Callitricho-Batrachion vegetation, which is the primary reason for designation. The River Itchen is a classic example of a sub-type 1 chalk river.

Macrophytes are key components of chalk ecosystems, significantly influencing the physical stream environment and the structure and functioning of stream ecology, providing food, habitats, refugia for riverine fauna and influencing biochemical cycles, hydrological properties and sediment dynamics at the local scale. As a result of the specific physicochemical conditions in chalk streams, chalk macrophyte communities frequently present a typical assemblage, containing Ranunculus penicillatus ssp. pseudofluitans, Callitriche obtusangula, Callitriche stagnalis, Callitriche platycarpa, Berula erecta, Oenanthe fluviatilis and, Rorippa nasturtium-aquaticum, as dominant taxa.

Ranunculus penicillatus ssp. Pseudofluitans is of particular importance as the keystone chalk stream macrophyte. It is of particular interest due to its dominance within the community where it improves flow and habitat heterogeneity. It provides refugia and support for macroinvertebrates and other riverine fauna; it is a sensitive indicator of prevailing environmental conditions.

7 Environment Agency (2016) Renewal of the Candover Scheme Abstraction Licence: Part 2 – Environmental Sustainability. 8 Rushbrook (2014) Crayfish Conservation in Hampshire’s Chalk Streams.

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Baseline Macrophyte data from the Environment Agency are available for the monitoring sites listed in Table 3.

Table 3 Macrophyte monitoring in the River Itchen Site name NGR Data Range Section 19 d/s Norris Bridge SU4761024450 2004-2009 Section 21 u/s Highbridge SU4659021540 2003-2009 Section 22 d/s Highbridge SU4684021060 2002-2009 Section 23 Stoke Common SU4607020580 2002-2009 Section 25 u/s Bishopstoke SU4663018670 2002-2010 Section 26 Chickenhall u/s railway SU4676017780 2002-2009 Section 27 Chickenhall d/s railway SU4636017230 2002-2010 Section 28 u/s Gaters Mill SU4536015640 2004-2009 Understanding the baseline macrophyte community upstream and downstream of Southern Water’s Lower Itchen sources and Portsmouth Water’s Gaters Mill source will help to assist with the assessment of the potential impacts of application of the drought orders. Due to the braided nature of the river channel, none of the sample locations provide an assessment of the macrophyte community at a point representative of the whole flow in the river but, cumulatively, the Itchen macrophyte monitoring points provide a baseline of species composition throughout the river.

Species lists for the site at section 19 d/s Norris Bridge, which is upstream of the Otterbourne abstraction, demonstrate a typical chalk river with dominant instream taxa of Ranunculus sp, Callitriche spp. and Berula erecta. High levels of Cladophora sp. and Vaucheria sp. suggest nutrient enrichment may be a problem in this section of river.

The species lists for all monitoring sites downstream of the Otterbourne abstraction - from Section 21 u/s Highbridge to section 27 at Chickenhall d/s of the railway - indicate a similarly typical chalk stream assemblage with dominant instream taxa of Ranunculus sp, Callitriche spp. and Berula erecta. Berula erecta cover decreases significantly in a downstream direction and is almost absent from section 26 at Chickenhall u/s of the railway and only present with much lower cover downstream of this point, illustrating the downstream increasing gradient of flow. Whilst it is evident that the community structure varies spatially throughout the river, the core taxa present remain consistent between the monitoring sites and the typical chalk stream assemblage is maintained throughout.

A fast species turnover was observed in all reaches with high diversity over the long-term but small number of taxa at any one survey.

The Itchen u/s of Gaters Mill still supports a typical chalk stream community dominated by Ranunculus sp. Calitriche sp and Oenanthe fluviatilis. Compared to sites further upstream, Berula erecta cover has declined and Cladophora sp. has increased.

No macrophyte data are available for the reach downstream of Gaters Mill. This may be due to the highly modified and canalised reach immediately downstream at Riverside Park, which is likely to support a much restricted macrophyte community due to morphological as well as hydraulic constraints. Immediately downstream of Riverside Park is the natural tidal limit; it is likely that the typically chalk stream community will begin a transition downstream of Riverside Park in favour of a more tidally-influenced, transitional water macrophyte community.

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Assessment A number of standard community metrics were provided with the Environment Agency macrophyte data:

 MTR – Mean Trophic Rank describes the trophic status of a site. The MTR increases with decreasing eutrophy, with a theoretical maximum of 100 and a minimum of 10.  MFR - Macrophyte Flow Rank calculates the dominant flow character of the community reflected by the assemblages present in the survey reach (after Holmes, 1999). Each species is assigned a flow rank based on their preference for low or high flow; these are combined with abundance and cover measures to provide an overall MFR.  RMHI describes community preference for flow conditions on a scale of 1 to 10. A score of 10 would indicate a plant community that has a preference for very slow flow or no-flow conditions, while scores of 1 are found in plant communities with a preference for very fast flows;  RMNI is designed to categorise macrophyte community preference to nutrient levels. Scores range from 1 to 10 with scores of 1 representing plant communities with preference for very low levels of nutrients and 10 representing communities with a preference for very enriched conditions;  NaTAXA is a community richness index and simply describes the number of truly aquatic taxa present. Higher values represent a more diverse and rich aquatic plant community;  NFG is another richness/diversity index and describes the number of functional macrophyte groups existing within a surveyed plant community. Twenty-four different functional groups (FG) have been defined. The higher the NFG value, the more diverse and rich the plant community is considered to be. Only taxa that are obligate hydrophytes (i.e. truly aquatic) are assigned scores under the NaTAXA and NFG scoring systems.

Table 4 provides a summary of reach-based indices for the macrophyte monitoring sites closest to the Southern Water and Portsmouth Water abstraction sources with upstream and (where available) downstream sites included in this assessment. For Otterbourne, these sites are ‘upstream - section19 d/s Norris Bridge’ and downstream ‘section 21 upstream of Highbridge’. For Gaters Mill, only upstream data exist – the site ‘upstream of Gaters Mill’. Indices are averaged over the available data period. Providing a mean index value for the reach could mask inter-year variability so the inclusion of minimum and maximum value for each index in Table 4 provides an indication of this range and therefore the variability behind the mean index value.

The summary community indices reveal very little difference between the sites upstream and downstream of Otterbourne. The RMNI and RMHI provide community level scores which account for variation in the number of taxa recorded, providing a robust classification of the overall flow and nutrient preference of the community. The range apparent within RMNI and RMHI is small and provides confidence that the mean values presented are meaningful in terms of summarising macrophyte community characteristics at each site.

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Table 4 Environment Agency macrophyte monitoring sites: summary of community indices within the hydrological zone of influence of the drought orders MTR MFR RMNI RMHI NFG NaTAXA

Upstream of Otterbourne (no of samples = 14) MEAN 42.3 2.1 7.6 7.5 6.8 13.2 MIN 32.7 1.9 7.2 7.2 6.0 10.0 MAX 46.9 2.5 8.0 7.9 8.0 16.0 Downstream of Otterbourne (no of samples = 15) MEAN 41.5 2.2 7.6 7.6 7.6 13.3 MIN 36.7 2.0 6.9 7.0 6.0 9.0 MAX 50.0 2.4 8.1 8.0 10.0 18.0 Upstream of Gaters Mill (no of samples = 9) MEAN 36.5 2.2 7.7 7.7 9.4 15.0 MIN 30.8 2.1 7.2 7.1 7.0 10.0 MAX 40.0 2.5 8.1 8.1 12.0 22.0 No data available downstream of Gaters Mill Note: Upstream of Otterbourne is sample point ‘Section 19 d/s Norris Bridge’ and downstream of Otterbourne is sample point ‘Section 21 upstream of Highbridge’. The high mean RMNI values suggest that, both upstream and downstream of Otterbourne, the macrophyte communities are adapted to mesotrophic (moderate) to eutrophic (high) nutrient conditions. Similarly, the high mean RMHI values suggest that both reaches support communities that are adapted to low to moderate flow velocities.

The indices upstream of Gaters Mill show similar ranges to those further upstream but with a lower MTR and similar adaptation to high nutrient and low flow velocities. A greater disparity in the NFG and NaTaxa recorded at Gaters Mill could suggest a richer and more diverse community present at Gaters Mill - it is worth noting that these indices are more readily influenced by a range of abiotic factors (e.g. shading, weed management and grazing) that can alter communities directly (through removal) and indirectly (through reduced habitat availability).

Flow variable impacts on Macrophyte assemblages Plant distribution is influenced by many physical and chemical factors including: flow; nutrient availability; light availability; shading; turbidity; substrate and temperature. Biological interactions, such as competition, grazing and seasonal management also influence the plant distribution. Flow conditions are considered a key determining factor affecting macrophyte distribution, particularly within the Ranunculion fluitantis and Callitricho-Batrachion communities in chalk streams9. Typically as flows increase, chalk submerged macrophyte dominance shifts between Ranunculus spp., Berula erecta and Callitriche spp. depending on flow conditions and other in-stream factors10.

9 Poynter, A.J.W. (2013) Impacts of environmental stressors on the River Itchen Ranunculus community. A thesis submitted to the University of Birmingham for the degree of Doctor of Philosophy. Available at http://etheses.bham.ac.uk/5112/1/Poynter14PhD.pdf 10 Wright, J. F., Clarke, R. T., Gunn, R. J. M., Kneebone, N. T. & Davy-Bowker, J. (2004). Impact of major changes in flow regime on the macroinvertebrate assemblages of four chalk stream sites, 1997-2001. River Research and Applications 20, 775-794.

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Investigations progressed under the Habitats Regulations RoC Stage 3 Appropriate Assessment11 and Stage 4 Site Action Plan12 considered the possible use of macrophytes to set target flow regimes for the River Itchen. It was concluded that an approach based on macrophyte data would be severely limited by the lack of robust data on which to base meaningful and defensible analysis and interpretation (i.e. the direct response of macrophyte communities to flow could not be quantified such that a meaningful target flow regime could be developed). In addition, it was noted that macrophyte communities on the River Itchen are strongly influenced by non-flow related factors, some of which are controlled by land and river bank management practices.

Cranston and Darby13 completed a review of the literature that assesses the many influences affecting the growth and distribution of Ranunculus spp in chalk rivers and concluded that water velocity was shown to be of prime importance due to the high photosynthetic rate of Ranunculus spp: fast flows are required to deliver oxygen and carbon to the plant. Velocity also acts indirectly to remove potentially competitive or shading algae, as well as clearing silt from gravels. Key drivers or influences upon velocity comprise natural climate cycles, abstraction, channel over-widening and impoundment. A reduction in velocity can have detrimental effects on Ranunculus spp.

Velocity is a prime factor for Ranunculus spp. all year around; critical thresholds of optimal velocities and discharges will vary seasonally according to the life-cycle of the plant. In summer, sufficient flow is necessary to provide good conditions for growth; over winter, peak flows are important to clear the senescent vegetation and silt. The timing of the autumn/winter increase in discharge is important, leading to higher or lower Ranunculus spp survival the next year14. Once established, the plant itself exerts an influence on the hydrological environment around it, changing the velocity passing through, over and under the plant and providing very specific micro-niches exploited by its associated macrophyte and macroinvertebrate community. They also provide refuges and a feeding resource to fish communities.

Table 5 sets out the velocity bands for optimum Ranunculus spp growth in the summer season reported in studies undertaken on chalk rivers (13,15,16,17).

Table 5 Velocity bands for optimum Ranunculus spp growth in the summer season Growth Band Velocity Notes Below optimum growth <0.1 m/s Acceptable growth 0.1 to 0.3 m/s the presence of other environmental conditions may affect growth (such as shading, competition from other plants etc.) Optimal growth 0.3-0.5 m/s Below optimal growth >0.5 m/s Exceeding the summer upper boundary may cause mechanical stress

11 Environment Agency (2005) River Itchen SAC. Habitats Regulations Review of Consents Stage 3 Appropriate Assessment. Environment Agency 12 Environment Agency (2007) River Itchen SAC Stage 4 Site Action Plan. 13 Cranston E. and Darby E. (2004) Ranunculus in Chalk Rivers: Phase 2. Environment Agency Science Report W1-042/TR 14 Dawson, FH. Castellano, E. Ladle, M. (1978 The seasonal effects of aquatic plant growth on the flow of water in a stream.—Proc. Eur. Weed Res. Soc. 5th Int. Symp. Aquatic Weeds, Wageningen, p. 71 to 78. 15 Atkins (2005) River Kennet SSSI Low Flows Investigation Final Report. For Thames Water 16 Southey, J., (2004) River Kennet Macrophyte Flow Study Final Report. November 2004. Scott Wilson KirkPatrick. Report to Thames Water Utilities plc. 17 Poynter, A.J.W. (2013) Impacts of environmental stressors on the River Itchen Ranunculus community. A thesis submitted to the University of Birmingham for the degree of Doctor of Philosophy. Available at http://etheses.bham.ac.uk/5112/1/Poynter14PhD.pdf

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It should be noted that while these velocity values relate to summer/low flow conditions, the lifecycle of Ranunculus spp has adapted to the normal seasonal pattern of the hydrological cycle. Thus, it is worth noting that for any particular year, even if summer velocities are optimal, growth may be sub- optimal if the antecedent velocities in the previous winter were insufficient. Strong autumn flows are needed to clear the senescent seasons’ growth, to flush out any sediment that has built up around the plants and to prepare the gravels for the new cycle of growth.

While it is recognised that high antecedent winter velocities are required for healthy Ranunculus spp growth in the following summer, there is no guidance available that quantifies the range of suitable velocities. It should be noted that in drought conditions, dependent on the specific seasonality of the low flows, high antecedent winter velocities may well be absent - with or without abstraction and drought orders.

Research on Ranunculus growth related to flow on the Itchen18 confirmed the velocity bands presented in Table 5 but also showed that, while growth was very limited in zero flows and even dewatered conditions, over a month long period the plants did not senesce but adopted a semi- amphibious form that was stumpy with short, stunted, untidy leaves. This highlights a potential drought coping mechanism that, at least in the short term, may prove a useful strategy in dealing with low flow situations18.

The phenology of Ranunculus spp. is most strongly influenced by seasonality, with extension and growth occurring during the spring, maturation in the summer, senescence in late autumn and dormancy in the winter. This annual growth pattern likely allows R.pseudofluitans to adapt to varying conditions by allowing vegetative dispersal (under favourable conditions sexual reproduction predominate)18. This growth pattern allows for rapid changes in dominance between the key macrophyte species within the community to respond to changing environmental conditions, including flow. These changes can adjust rapidly to changing conditions (such as extreme drought) and will be reversed once the conditions revert to the status quo.

Velocities and depths in the Itchen SAC Table 6 presents indicative calculations of velocities experienced in the River Itchen with flows at the licence HOF and the drought order reduced HOF. While there are a number of uncertainties that need to be borne in mind, these calculations give a reasonable indication of the sensitivity of velocities and water depths to changes in low flow, and specifically the reduction in flow from the licence HOFs to drought order HOFs for the Lower Itchen. Full details of the method used to derive these estimations and their limitations are presented in Appendix B of the EAR.

The main points to take from the Table 6 are:

 Velocities at all but three cross-sections are estimated to be above 0.3 m/s, both for the licence HOFs and the proposed drought order HOFs. At the three cross-sections where velocities are estimated to be below 0.3 m/s, the change in velocity between the licence HOF and the proposed drought order HOFs is very small (0.01 to 0.02 m/s).  Water depths at all but one cross-section are estimated to be above 0.4 m both for the licence HOF and the proposed drought order HOFs. At the cross-section where the depth is estimated to be below 0.4 m, the change in depth between the licence HOF and the proposed drought order HOFs is very small (0.04 m).  The significance of the changes in velocity become apparent when compared against the velocity bands for optimum Ranunculus sp growth presented in the previous section. There are no cross-sections where the velocities drop below the acceptable range for Ranunculus

18 Poynter, A.J.W. (2013) Impacts of environmental stressors on the River Itchen Ranunculus community. A thesis submitted to the University of Birmingham for the degree of Doctor of Philosophy. Available at http://etheses.bham.ac.uk/5112/1/Poynter14PhD.pdf

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sp growth. The vast majority of sites demonstrate optimum, or borderline higher than optimum, velocities even with the implementation of the drought orders. Of the three locations with acceptable flow velocities, the flow velocities never achieve optimum even at the licence HOF and the impact of the drought orders is to reduce the velocity by just 0.02 m/s. Table 6 Indicative calculations for the relationship between low flows, depths and velocities - River Itchen from Otterbourne to Gaters Mill and downstream of Gaters Mill ISIS model Inflow / Flow at Velocity Velocity Depth Depth cross-section HOF (Ml/d) Section (m/s) change (m) change node and (Ml/d) (m/s) (m) reach description 28.008 198 149 0.41 -0.02 0.64 -0.04 Otterbourne to Highbridge 160 120 0.39 0.60 28.022 198 149 0.24 -0.02 0.98 -0.09 Otterbourne to 160 120 0.22 0.89 Highbridge 28.034 198 149 0.35 -0.02 0.47 -0.04 Otterbourne to 160 120 0.33 0.43 Highbridge 28.040 198 149 0.37 -0.03 0.40 -0.03 Otterbourne to 160 120 0.34 0.37 Highbridge 28.058 198 149 0.20 -0.01 0.85 -0.07 Highbridge to 160 120 0.19 0.78 Chickenhall 02.226 198 198 0.22 -0.01 0.97 -0.07 Highbridge to 160 165 0.21 0.90 Chickenhall 02.247 198 149 0.51 -0.03 0.83 -0.07 Highbridge to 160 120 0.48 0.76 Chickenhall 02.261 198 218 0.42 -0.02 0.60 -0.05 Chickenhall to 160 180 0.40 0.55 Gaters Mill 01.046 198 218 0.55 -0.03 0.77 -0.06 Chickenhall to 160 180 0.52 0.71 Gaters Mill 01.031 198 218 0.51 -0.02 0.92 -0.06 Chickenhall to 160 180 0.49 0.86 Gaters Mill 01.020 194 0.47 -0.03 0.69 -0.05 Gaters Mill to Riverside Park 150 0.44 0.64 01.009 194 0.54 -0.03 0.91 -0.06 Gaters Mill to Riverside Park 150 0.51 0.85 01.003 194 0.55 -0.04 0.69 -0.07 Riverside Park to Woodmill 150 0.51 0.62

16 Appendix D Environmental Features Assessment

 The range of depths experienced in the river remain suitable for Ranunculus sp. growth throughout the range of flows that are considered at the HOF with and without the drought orders in place. The impact of the drought orders on the shallowest waters is to reduce the water depth by 4 cm – this change in water depth is likely to be insignificant to Ranunculus sp. communities which will modify the water depths by their growth patterns in any case.  Figure 7 of Appendix B of the EAR provides an initial understanding as to the likely scale and frequency of flow impacts associated with the drought orders under historical climate conditions (1918 – 1997). The figure illustrates that neither the Lower Itchen sources nor the Gaters Mill drought orders would have been required under the historical climatic conditions examined as neither the Allbrook & Highbridge or Riverside Park licence HOFs are breached.  Assessing drought severities greater than those experienced in the historical record requires the use of stochastic flow time series data. Analysis of the stochastic time series data indicates that the frequency with which abstraction from the Gaters Mill and Lower Itchen sources would be needed below the licence HOFs is approximately 1 in 130 to 1 in 170 years. This assumes that the Testwood and Candover Augmentation Scheme Drought Orders have been already implemented. This suggests that in the Lower Itchen the Ranunculus spp will only be put under flow related stress very infrequently.

Summary - Annex I habitat The main points to be taken from the above assessment are:

 The Itchen from Norris Bridge (upstream of Otterbourne) to upstream of Gaters Mill supports a typical chalk stream assemblage dominated by the keystone species Ranunculus penicillatus ssp. Pseudofluitans.  Based on macrophyte community indices, the resident macrophyte community is adapted to low flows and nutrient enrichment.  No macrophyte data are available for the river downstream of Gaters Mill – it is noted that the river downstream of Gaters Mill at Riverside Park is canalised with highly modified geomorphology and hydraulic conditions. Downstream of Riverside Park is the natural tidal limit of the river. These reaches downstream of Gaters Mills to the tidal limit are not likely to support typical chalk stream macrophyte communities.  Research into Ranunculus sp communities and Ranunculus sp growth patterns indicate that both are sensitive to velocity changes. Ranunculus penicillatus ssp. Pseudofluitans has been shown to change morphology during growth in direct response to velocity changes and the typical chalk stream assemblages have been shown to change species composition in response to changing velocities in rivers.  Well-established optimum and acceptable velocity bands have been identified from a range of literature and research sources giving acceptable velocities for Ranunculus sp. growth between 0.1-0.3 m/s and optimal conditions between 0.3-0.5 m/s. Above 0.5 m/s, growth is sub-optimal and plants may be susceptible to damage.  Indicative calculations of velocities based on flow conditions in the river suggest that at all but three cross-sections studied downstream of Otterbourne, velocities are estimated to be above 0.3 m/s both for the licence HOFs and the proposed drought order HOFs. At the three cross-sections where velocities are estimated to be below 0.3 m/s, the velocity was still within the upper end of the acceptable range.  The change in velocity between the licence HOFs and the proposed drought order HOFs is very small (0.01 to 0.02 m/s).  Hydrological modelling show that implementation of the Gaters Mill and Lower Itchen sources drought orders would be required very rarely, assuming that the Testwood and Candover Augmentation Scheme drought orders have already been implemented.

17 Appendix D Environmental Features Assessment

On the basis of the above assessment, it is anticipated that although mechanisms exist for flow- related impacts on macrophytes and their related communities, any impacts on the Ranunculus spp. communities of the Lower Itchen as a result of the implementation of the drought orders would be infrequent and are likely to be minor and reversible.

Atlantic salmon Atlantic salmon are an Annex II species in the Habitats Directive which are present in the River Itchen SAC as a qualifying feature, but not a primary reason for site selection.

Baseline River Itchen salmon have a relatively short life-cycle compared to non-chalk stream populations with many juvenile salmon remaining in the river for only one year and most returning adults spending only one year at sea. The reason for the short period of growth in freshwater is due to the high growth rates that these fish can achieve in the rich chalk stream habitat.

Adult salmon enter the River Itchen to spawn. Spawning takes place in the winter (mainly December and January), but the fish enter the river many months before this, typically between May and August. Fish enter the non-tidal river at Wood Mill Pool whereupon some fish move rapidly up the river and past Gaters Mill towards the spawning areas while most hold up in the lower river. Observations of salmon migration through the reach between Woodmill Pool and Gaters Mill during a tagging study in 1990-199419 indicated that the rate of migration was highly variable. The fastest salmon transferred through the reach in less than an hour while some salmon took over 100 days. Catches in the river suggest that peak movements upriver occur between June and September (Salmonid and Freshwater Fisheries Statistics for England and Wales, 2010-16).

Atlantic salmon populations in the River Itchen are in unfavourable condition and have been very low in the 1990-2003 period. The EA calculate a Conservation Limit for salmon in the Itchen which is the approximate minimum number of adult spawning salmon required for a self-sustaining population of salmon. This Conservation Limit equates to approximately 660 returning adults19. The EA also calculate an egg conservation limit which is the approximate minimum number of eggs deposited that are required for a self-sustaining population of salmon in the Itchen and this equates to 1.63 million eggs. Returning adults and egg deposition rates since 2004 have been recovering and since 2010 have been close to or exceeded these conservation limits.

The reasons for the low population size are thought to be due to several important factors including poor egg survival and poor marine survival, as well as exploitation in the lower reaches of the river. The recovery is, in part, attributed to catch and release schemes introduced by anglers in the 1990s. The concern is that a reduction in river flows may prevent or delay the movement of salmon into and through the river and that this could lead to increased losses or lower spawning success compared to fish entering and moving up the river promptly.

Potential flow-related Impacts Due to the complexity of the Atlantic salmon life-cycle, there is a concern that it is slow to recover from impacts. Factors thought to be significant in the riverine habitat with respect to salmon survival are diffuse pollution, siltation of the salmon redds, summer low flow with respect to habitat suitability, entry to the river and migration up the river. Deterioration in water quality (e.g. temperature, ammonia and dissolved oxygen) could also have direct physiological effects on Atlantic salmon.

Diffuse pollution issues are largely attributed to the Upper Itchen and beyond the potential impact of the drought orders.

19 Environment Agency (2004) River Itchen Sustainability Study, November 2004

18 Appendix D Environmental Features Assessment

Several studies have shown that spawning gravel areas of the River Itchen are in poor condition20,21 with egg survival rates often less than 5%. The Environment Agency has initiated a programme of gravel cleaning on the Itchen to tackle this issue. High river flows will help to clean the gravels and transport silt past the spawning gravels but the spawning areas are largely upstream of Southern Water’s Lower Itchen sources and so this is not considered to be a major issue for the environmental assessment of the drought orders.

The RISS study22 noted that the success of river entry has been associated with a number of factors including low river discharge, high water temperatures and low dissolved oxygen23,24 and river discharge is widely reported to influence the upstream migration of salmon25,26,27,28.

It is perhaps significant to note that it is unclear how salmon perceive changes in river discharge. Various hypotheses have been proposed including water velocity, the character of the water (smell or taste) or even the water temperature. At present there seems to be no clear consensus on this point but observations made by salmon experts Fewings and Solomon22, noted that apparently stimulated migration occurred hours before any detectable change in river discharge. This suggests that salmon are stimulated by a change in some character of the water rather than the change in discharge per se.

Considerable robust scientific analysis has been ongoing on the neighbouring River Test to investigate the relationship between river discharge (and associated metrics) and salmon movements within the river. While it is recognised that there is wide variation in the relationships between river discharge and upstream migration of salmon between different rivers27,28, it is useful to consider the most recent outputs from this analysis in the context of River Itchen – another similarly stable flow, high base flow index (BFI) river.

Milner and Fenn29 concluded for the studies on the River Test that:

 “flow-related control on salmon movement is not strong, for the Great Test. Moreover, there is evidence that in large, stable flow, high BFI rivers such as the Test, flow-migration responses may be inherently weaker compared to those exhibited by salmon in surface water fed rivers.”  “No evidence was found of clear migration-inhibiting or migration-triggering thresholds (in flow or other variables) in the work we have done. For migration to occur, the enabling hydraulic conditions (notably water flow, depth and velocity) need to be present; but the occurrence of such enabling conditions does not mean that migration will occur. The

20 Scott A & Beaumont W R C (1994). Improving the survival rates of Atlantic salmon (Salmo salar L.) embryos in a chalk stream. Institute of Fisheries Management Annual Study Course, 1993, Cardiff. 21 Environment Agency (1998) River Itchen Salmon Action Plan. River Itchen May 1998. 22 Environment Agency (2004) River Itchen Sustainability Study, November 2004 23 Clarke D.R.K., Evans D.M., Ellery D.S., and Purvis W.K. (1994) Migration of Atlantic salmon (Salmo salar L.) in the River Tywi estuary during 1988, 1989 and 1990. NRA Cardiff, Report RT/WQ/RCEU/94/7, 1994 24 Purvis, W., Crundwell, C. R., Harvey, D., Wilson, B. R., (1994), Estuarial Migration of Atlantic Salmon in the River Dee, North Wales. ETSU T/04/00154/REP Report by the National Rivers Authority for the Energy Technology Support Unit, pp. 134. 25 Banks, (1969) A Review of the Literature on the Upstream Migration of Adult Salmonids. Journal of Fish Biology. Volume 1. Pp.85 - 136 26 Hellawell J.M., Leatham H., and Williams G.I. (1974) The upstream migratory behaviour of salmonids in the River Frome, Dorset. Journal of Fish Biology. Volume 6, Issue 6, November 1974, pp 729–744 27 Solomon, D.J, Sambrook, H.T., Broad, K.J, 1999. Salmon migration and river flow. Environment Agency R & D Publication 4. pp 110 28 Baxter G. (1961) River utilization and the preservation of migratory fish life. Proc Inst Civil Eng 18:225–244 29 Milner N. and Fenn C. (2017) Joint statement on the outcomes of and pointers from advanced regression and time series modelling of salmon migration count responses to flow in the Great Test. In: Testwood Enabling Works Phase 1 Scoping Report, Atkins for SWS

19 Appendix D Environmental Features Assessment

indications are that rainfall and flow are partial influences that work in conjunction with other factors in a highly variable, and perhaps irreducible fashion”.  The evidence points to the conclusion that flow dynamics exert limited influence on migration counts in the Great Test.

Indirect flow related impacts - Temperatures and Dissolved Oxygen Salmonids in the UK’s southern chalk streams are operating at the edge of their range particularly with regard to water temperature. Alabaster and Lloyd30 identified water temperatures above 20- 21oC as being damaging to salmonids and Shephard31 suggested mortality occurs at temperatures greater than 23oC. The acclimation of the fish and duration of exposure was important to the effect that was observed31.

High river temperatures often coincide with low river discharge as dry summers often have high air temperatures. Studies on the neighbouring River Test indicated that in-river water temperature is largely dictated by air temperatures and that abstraction had minimal impact on water temperatures.

Alabaster et al32 reported that water temperature was an important factor in determining the lethality of low dissolved oxygen concentrations. Salmon were able to survive dissolved oxygen concentrations of 3.2 mg/l at 15ºC but that at 22.5ºC, a dissolved oxygen concentration of approximately 5.7 mg/l was required for survival.

Water temperatures in the Itchen estuary show maxima of around 20-21oC during July, August and September which could be problematic to the migrating salmon if deep cool water is not available for refuge. Nevertheless, dissolved oxygen concentrations found in the River Itchen estuary and Southampton Water are typically high (Environment Agency data show dissolved oxygen concentration stayed above 6 mg/l throughout 2017 in the Test Estuary and Southampton Water) which suggests that they should provide some protection to the salmon.

Indirect flow related impacts - Food availability

Juvenile Atlantic salmon grow rapidly in chalk streams due to the high abundance of macroinvertebrates as foods sources. They typically therefore only spend one year in the river as juveniles (Parr) before they migrate out to sea as smolts.

Studies from the River Itchen and other rivers suggest that Gammaridae and Baetidae are important food supply to salmonids33,34. They are a particularly important food source in autumn and winter due to their higher abundance at this time34. Sodergren35 concluded that a decrease in the population of juvenile salmon was directly related to reductions in the abundance of prey items (particularly winter growing Ephemeropteran nymphs such as Baetis rhodani).

30 Alabaster J.S. and Lloyd R. (1982) Water Quality Criteria for Freshwater Fish. Butterworth-Heineman 31 Shepard, S.L.(1995). Atlantic salmon spawning migrations in the Penobscot River, Maine- Fishways, flows and high temperatures. M.S. Thesis, University of Maine, Orono, ME. 111 p. 32 Alabaster J.S., Gough P, and Brooker W.J. (1991) The environmental requirements of Atlantic salmon, Salmo salar L., during their passage through the Thames Estuary, 1982–1989, Journal of Fish Biology, Volume 38, Issue 5, May 1991, pp 741–762. 33 Exley K. (2006) River Itchen Macro-Invertebrate Community Relationship To River Flow Changes, Environment Agency Report, October 2006 34 MacNeil, C., Elwood, R.W. and Dick, J.T.A. (2000). Factors influencing the importance of Gammarus spp. (Crustacea: Amphidoda) in riverine salmonid diets. Arch. Hydrobiologia 149, 87-107. 35 Sodergren, S. (1976). Ecological effects of heavy metal discharge in a salmon river. Report to the Institute of Freshwater Resources, Drottningholm 55, 91-131.

20 Appendix D Environmental Features Assessment

Studies on the Itchen macroinvertebrates suggested a flow threshold where the characteristic chalk stream community undergoes significant ecological change39. The initial community change is characterised by a drop in the typically very high abundances of the dominant taxa – particularly susceptible are the Gammaridae and Baetidae39.

The HOF of 198 Ml/d at Allbrook & Highbridge was devised to offer a sufficient level of protection to safeguard the River Itchen macroinvertebrate community. Reducing the flow to 160 Ml/d due to the Lower Itchen sources drought order may result in some short-term stress on the macroinvertebrate community; however, evidence from the River Itchen over the last 16 years or so suggests that the macroinvertebrate community is able to recover fairly rapidly from the impacts of low flows once higher flows return. The impacts of a dry summer will be limited to one year assuming that flows in the following summer return to more normal levels36.

Salmon are highly mobile and adaptable with regards to their food source; they are known to feed on simulidae and chironomidae which are abundant downstream of Southern Water’s Lower Itchen sources and more tolerant of low flow conditions. Flows above Otterbourne during drought conditions will be maintained initially by the operation of the Candover Augmentation Scheme drought order and therefore Baetidae, which are drift species, should still be present in the drift community from upstream of the Otterbourne abstraction.

The implications of a reduced food supply for one season, as the result of drought conditions, could be to reduce the numbers and growth rate of Parr as a result of:

 A longer freshwater growing period required to reach the minimum weight and fork length to smoltify and begin migration out of the river.  Larger territories required due to limited food supply and therefore a temporarily reduced carrying capacity. The carrying capacity for a river is the maximum number of fish that can be supported by the river. This is usually limited by competition because Parr are highly territorial.  In some cases, fewer fish may result in greater survival in that year - partly due to reduced fish density, larger territories and therefore reduced competition. There is currently no evidence of the impact of short term declines in abundance of flow sensitive macroinvertebrate food sources on the salmon population. Macroinvertebrate communities recover rapidly from periods of drought and alternative low flow tolerant species will continue to be available as food sources. A reduction in the numbers and growth of Parr in one year is unlikely to have a significant impact on the returning stock estimates for the Itchen salmon population in the longer term and should not impact on the recovery of the Itchen salmon population.

Habitat Variables: impacts of drought orders Table 6 (presented in section D.2.2.1.2 above) presents indicative calculations of velocities experienced in the River Itchen with flows at the licence HOFs and the proposed drought order HOFs. While there are a number of uncertainties that need to be borne in mind, these calculations give a reasonable indication of the sensitivity of velocities and water depths to changes in low flow, and specifically the reduction in flow from the licence HOFs to the drought order HOFs. Full details of the method used to derive these estimations and their limitations are presented in Appendix B of the EAR.

The main points to take from the hydrological assessment in Appendix B and the habitat variable results in Table 6 are:

36 Exley, K (2005). River Itchen macroinvertebrate community relationship to river flow changes. Environment Agency Report.

21 Appendix D Environmental Features Assessment

 Velocities at all cross-sections change very little from the licence HOFs and the proposed drought order HOFs (never more than 0.04m/s). At the three cross-sections where velocities are lowest (below 0.3 m/s), the change in velocity between the licence HOFs and the proposed drought order HOFs is very small (0.01 to 0.02 m/s).  Water depths at all cross-sections are suitable for fish passage, even at the shallowest cross- sections with the drought order HOFs in place. At the cross-section where the depth is estimated to be below 0.4 m, the change in depth between the licence HOFs and the proposed drought order HOFs is very small (0.04 m).  At several locations throughout the river downstream of Otterbourne and with the drought order HOFs in place, water depths suitable for holding up and salmon refuges are retained.  Hydrological modelling indicated that neither the Lower Itchen nor the Gaters Mill drought orders would have been required under historical climatic conditions examined with neither the Allbrook & Highbridge nor Riverside Park HOFs being breached.  Stochastic time series have been developed to assess the risk of requiring the drought orders under more severe drought conditions than have been experienced historically. Analysis of the stochastic time series flow sequences indicates that the frequency with which abstraction from the Lower Itchen sources would be needed below the licence HOFs is approximately 1 in 130 to 1 in 170 years. This assumes that the Testwood and Candover Augmentation Scheme Drought Orders have already been implemented. This suggests that Atlantic salmon will only be put under flow related stress very infrequently due to the Lower Itchen sources drought orders.

Summary – Atlantic salmon There are few data currently available for the Itchen salmon populations on which to base the assessment. Consequently, the assessment has taken into account the likely frequency and duration of the drought orders, the hydrological effects of the drought orders and the fact that there are a great range of environmental factors that influence Atlantic salmon migration and survival.

 Atlantic salmon populations in the River Itchen are in unfavourable condition and not achieving conservation limits.  The reasons for the poor performance of the Atlantic salmon population in the River Itchen are numerous and relate to spawning success and egg survival in the upper river, exploitation in marine and freshwaters, and marine survival.  Concern over the impact of the drought order largely relates to impact on the migration of salmon up the river and the potential for delays caused by low flows.  Robust statistical analysis of data on the neighbouring River Test indicate that there is evidence that in large, stable flow, high BFI rivers (such as the River Itchen), flow-migration responses may be inherently weaker compared to those exhibited by salmon in surface water fed rivers37.  Resumption of migration in autumn (typically October) is largely triggered by life-cycle drivers (e.g. physiological readiness to spawn) – at this time of year, only very small but distinct rainfall-induced increases in flow trigger migration. Drought in this period would affect these triggers but abstraction under the drought order would not remove these stimuli.  Since the restart of the spawning migration is unlikely to be affected by abstraction, the effect of the drought order is only likely to be small.

37 Milner N. and Fenn C. (2017) Joint statement on the outcomes of and pointers from advanced regression and time series modelling of salmon migration count responses to flow in the Great Test. In: Testwood Enabling Works Phase 1 Scoping Report, Atkins for SWS.

22 Appendix D Environmental Features Assessment

 Hydrological assessments have shown that the frequency of application of the drought orders will be very low: - Neither the Allbrook & Highbridge nor Riverside Park HOFs are breached during the historical climate conditions (1918 – 1997). - Analysis of the stochastic time series indicates that the frequency with which drought order abstraction from the Lower Itchen sources would be needed below the HOFs of 198 Ml/d and 194 Ml/d is approximately 1 in 130 to 1 in 170 years. This assumes that the Testwood and Candover Augmentation Scheme Drought Orders have already been implemented.  A hydraulic assessment of the habitat variables indicates that during the extreme 1:150 year drought conditions when a drought order application may require the HOF to be breached: - Velocities at all cross-sections change very little from the licence HOF and the proposed drought order HOFs (never more than 0.04 m/s). At the three cross-sections where velocities are lowest (below 0.3 m/s), the change in velocity between the licence HOF and the proposed drought order HOFs is very small (0.01 to 0.02 m/s). - Water depths at all cross-sections are maintained above 0.4 m and unlikely to be limiting to fish passage or make a significant change to holding up pools on which the salmon rely.  Itchen salmon are resilient to flow conditions prevalent in the Itchen. Depleted salmon populations can recover well once drought pressures are removed from a single drought, whilst repeated droughts may make recovery harder but they will recover in due course.  The marginal abstraction-induced effects over and above that of natural drought conditions on the long-term resilience and sustainability of the Itchen salmon population will not be significant. There are limited data on which to assess the impacts of the abstraction on the migratory salmon in the river. However, the low frequency of implementation of the drought orders and the modest impacts on habitat variables suggest that any impacts are likely to be very minor and reversible and should not impact on the recovery of the salmon population.

Southern damselfly The Southern damselfly Coenagrion mercuriale is a Habitats Directive Annex II species that is present in the River Itchen SAC as a primary reason for selection.

The Southern damselfly Coenagrion mercuriale has a long aquatic larval stage lasting typically for two years in the UK and accounts for 95% of the Southern Damselfly life cycle38. During this phase they have a preference for small streams on heathlands and old water meadow ditch systems on chalk streams.

The Southern Damselfly is on the northern edge of its range in Britain. It is restricted mainly to the south and west of the country with population strongholds in the water meadow ditch systems along the Itchen Valley. Their distribution is discontinuous because their preferred habitat has undergone considerable fragmentation over the last century.

A previous study on the River Itchen39 has suggested that larval southern damselfly were strongly associated with slow flowing, permanent water habitats in drainage ditches of the lower Itchen valley. Slightly less typically, the aquatic larvae were present in macroinvertebrate samples from Gaters Mill

38 Purse B. (2002) The Ecology and Conservation of the Southern Damselfly (Coenagrion mercuriale – Charpentier) in Britain. EA R&D Technical Report W1-021/TR 39 Environment Agency (2016) Renewal of the Candover Scheme Abstraction Licence: Part 2 – Environmental Sustainability.

23 Appendix D Environmental Features Assessment

on two occasions in 2005 and one in 2007; there are no other records in in-stream macroinvertebrate samples throughout the lower Itchen.

The aquatic larvae generally live amongst the roots and sediments of the marginal emergent vegetation. Soft-stemmed, submerged and semi-emergent herbs are favoured for oviposition whilst tall emergents with rigid upright stems are favoured for emergence.

Other habitats are characterised by ditches flowing through old water meadows, which themselves fall into the category of wet grassland and, where undermanaged, fen. In these habitats there are two key elements that sustain the species. The nature of the ditches is critical, and that includes many abiotic attributes such as water level, water velocity, and water chemistry, and biotic factors such as the structure and composition of emergent and marginal vegetation. Although implementation of the drought orders will be very infrequent, a reduction in and/or lowering of water levels could impact upon these habitats directly by affecting the river or by indirectly affecting the non-river habitats. The terrestrial nature of these habitats also sustains the species during their relatively short adult stage - typically and indirectly by affecting the ditch, its physical structure and the water therein.

Most of these drainage ditches are supplied with water from the main River Itchen via flow control structures. Abstraction under drought order powers could potentially reduce the availability of water in the main channel of the Itchen and therefore limit the supply of water to the drainage ditch habitats, although water level management is likely to be the primary control on ditch levels.

Hydrological assessments have shown that the frequency of drought order implementation will be very low:

 Neither the Allbrook & Highbridge nor Riverside Park HOFs are breached during the historical climate conditions (1918 – 1997).  The stochastic time series for Allbrook & Highbridge shows that the Lower Itchen sources and Gaters Mill drought orders would only be required very rarely.  A hydraulic assessment of the impact of the drought order reduced HOFs in comparison to the licence HOFs on the habitat variables indicates that during the rare events when abstraction may be required under drought order powers: - Velocities at all cross-sections change very little from the licence HOFs and the proposed drought order HOFs (never more than 0.04 m/s). At the three cross-sections where velocities are lowest (below 0.3 m/s), the change in velocity between the licence HOFs and the proposed drought order HOFs is very small (0.01 to 0.02 m/s). - Water depths at all cross-sections are maintained above 0.4 m and unlikely to be limiting to the macrophyte assemblages on which the damselfly rely in the main river. Due to the limited information on the southern damselfly distribution and status in the river and bounding wetlands, it cannot be concluded that the implementation of the drought orders are not likely to damage their populations. However, due to the low frequency of drought order implementation and the small magnitude of the changes to water depth and velocity in the river, the magnitude of impact of the drought orders beyond that of the prevailing drought conditions are anticipated to be low.

Otter, bullhead, lamprey and white-clawed crayfish The notified species that were found not to be significantly affected by abstraction licences in the RoC Appropriate Assessment were otter, bullhead and brook lamprey.

24 Appendix D Environmental Features Assessment

As already noted, although white-clawed crayfish were assessed as being affected by abstraction, their populations are constrained to the upper catchment and hence not affected by the proposed drought orders.

Detailed studies of otter on the River Itchen confirmed that the otter population was in favourable condition and their high mobility over tens of kilometres added to their resilience.

With regard to bullhead and brook lamprey, surveys have shown that both species occur throughout the catchment in habitat where they would be expected. Both are also considered to be relatively resilient to environmental stress and hence there is no likely significant effect from the application of the drought orders on these two fish species. D.2.3. Special Protection Areas D2.3.1 Solent and Southampton Water SPA D2.3.1.1 Baseline The Solent and Southampton Water SPA qualifies under Article 4.1 of the Directive (79/409/EEC) by supporting populations of European importance of the breeding bird species listed on Annex I of the Directive.

The site also qualifies under Article 4.2 of the Directive in supporting populations of European importance of migratory bird species. It further qualifies under Article 4.2 of the Directive by regularly supporting at least 20,000 waterfowl.

Table 7 Reasons for designation: details of the Solent and Southampton Water SPA qualifying features Criteria Detail Article 4.1 During the • Common Tern Sterna hirundo, 267 pairs representing at least breeding season 2.2% of the breeding population in Great Britain (5 year peak mean, 1993–1997) • Little Tern Sterna albifrons, 49 pairs representing at least 2.0% of the breeding population in Great Britain (5 year peak mean, 1993–1997) • Mediterranean Gull Larus melanocephalus, 2 pairs representing at least 20.0% of the breeding population in Great Britain (5 year peak mean, 1994–1998) • Roseate Tern Sterna dougallii, 2 pairs representing at least 3.3% of the breeding population in Great Britain (5 year peak mean, 1993–1997) • Sandwich Tern Sterna sandvicensis, 231 pairs representing at least 1.7% of the breeding population in Great Britain (5 year peak mean, 1993–1997) Article 4.2 over winter • Black-tailed Godwit Limosa limosa islandica, 1,125 individuals migratory species representing at least 1.6% of the wintering Iceland – breeding population (5 year peak mean, 1992/3–1996/7) • Dark-bellied Brent Goose Branta bernicla bernicla, 7,506 individuals representing at least 2.5% of the wintering Western Siberia/Western Europe population (5 year peak mean, 1992/3– 1996/7) • Ringed Plover Charadrius hiaticula, 552 individuals representing at least 1.1% of the wintering Europe/Northern Africa – wintering population (5 year peak mean, 1992/3–1996/7) • Teal Anas crecca, 4,400 individuals representing at least 1.1%

25 Appendix D Environmental Features Assessment

Criteria Detail of the wintering Northwestern Europe population (5 year peak mean, 1992/3–1996/7) Assemblage qualification: A The area qualifies under Article 4.2 of the Directive (79/409/EEC) wetland of international by regularly supporting at least 20,000 waterfowl importance Over winter, the area regularly supports 53,948 individual waterfowl (5 year peak mean 1991/2–1995/6) including: Gadwall Anas strepera, Teal Anas crecca, Ringed Plover Charadrius hiaticula, Black-tailed Godwit Limosa limosa islandica, Little Grebe Tachybaptus ruficollis, Great Crested Grebe Podiceps cristatus, Cormorant Phalacrocorax carbo, Dark-bellied Brent Goose Branta bernicla bernicla, Wigeon Anas penelope, Redshank Tringa totanus, Pintail Anas acuta, Shoveler Anas clypeata, Red-breasted Merganser Mergus serrator, Grey Plover Pluvialis squatarola, Lapwing Vanellus vanellus, Dunlin Calidris alpina alpina, Curlew Numenius arquata, Shelduck Tadorna tadorna. Source: JNCC website: http://jncc.defra.gov.uk/page-2037

D2.3.1.2 Assessment Although there is a minor theoretical pathway for drought impacts on wading birds, and other birds, the operation of the drought order during prevailing drought conditions is unlikely to impact waders significantly more than would arise under the prevailing drought conditions. If the breeding and feeding resource is susceptible to drought, it is already likely to be impacted by the drought conditions; the implementation of the drought orders will not affect the tidal regime or elicit significant impacts on salinity gradients that could trigger a significant impact pathway. At the end of a drought, when significant rainfall occurs, recovery should be rapid.

Taking these considerations into account, the incremental impact of the drought orders beyond that of the prevailing drought conditions is not likely to have a significant effect on the qualifying features of the Solent and Southampton Water SPA.

D 2.3.2 Solent and Dorset Coast potential Special Protection Area (pSPA) D.2.3.2.1 Baseline Natural England, upon reviewing information from the JNCC breeding seabird data within the Solent and Dorset Coast, has identified a marine area and species that need to be considered for protection. The recommendations developed so far propose a new marine designation for three species of bird; common, sandwich and little tern.

The potential SPA (pSPA) site is located on the south coast within the English Channel. The site is approximately 259.7 nm2 (89,078.02 Ha) in area and extends from the Isle of Purbeck in the West to Bognor Regis in the East, following the coastline on either side to the Isle of Wight and into Southampton Water.

There are already four SPAs within the Greater Solent that are designated for breeding terns. These are the Chichester & Langstone Harbours SPA (for Sandwich and Little tern), the Solent and Southampton Water SPA (for Common, Sandwich and Little tern) and Pagham Harbour SPA (Little tern). The fourth associated SPA lies within Poole Harbour (Common Tern and Sandwich tern). The new potential SPA covers the area that the breeding terns use for foraging during April - September. Whilst management measures are already in place in this foraging area due to the existing SPAs, the classification of this new site will provide clarity to stakeholders about the areas that the terns forage within and the species that require consideration.

26 Appendix D Environmental Features Assessment

The recommendations developed so far propose a new marine designation which will include the sub-tidal areas not currently encompassed in the existing SPAs. It will have its landward boundary at mean low water (MLW) where it abuts any existing SPA where terns are already a feature.

D.2.3.2.2 Assessment Although the pSPA is not yet in place it may be confirmed within the timeframe of the draft Drought Plan 2018. The tern species in the pSPA are already a feature in the Solent and Southampton Water SPA and, as such, assessments protecting the Solent and Southampton Water SPA should also provide sufficient protection for the pSPA.

Although there is a minor theoretical pathway for impact on the breeding terns, the operation of the drought order during prevailing drought conditions is unlikely to impact the breeding terns significantly more than the prevailing drought conditions as the breeding and feeding resource is likely to already be impacted by the drought conditions. Drought order implementation will not affect the tidal regime or elicit significant impacts on salinity gradients that could trigger a significant impact pathway.

Taking these considerations into account, the incremental impact of the drought orders beyond that of the prevailing drought conditions is not likely to have a significant effect on the qualifying features of the Solent and Dorset Coast pSPA. D.2.4. Ramsar D.2.4.1 Solent and Southampton Water Ramsar Site D.2.4.1.1 Baseline

The Solent and Southampton Water Ramsar site has the same area as the SPA. A summary of the four Ramsar-qualifying features (taken from the Ramsar Information Sheet, Version 3 June 2008) are detailed in Table 8 – all the features for which the site is designated are downstream of the influence of the River Itchen abstractions.

Table 8 Reasons for designation: Solent and Southampton Water Ramsar site qualifying features Criteria Detail Criterion 1 (A representative, The site is one of the few major sheltered channels between a rare, or unique example of a substantial island and mainland in European waters, exhibiting natural or near natural an unusual strong double tidal flow and has long periods of slack wetland type found within water at high and low tide. It includes many wetland habitats the appropriate bio- characteristic of the biogeographic region: saline lagoons, geographic region) saltmarshes, estuaries, intertidal flats, shallow coastal waters, grazing marshes, reedbeds Criterion 2 (it supports The site supports an important assemblage of rare plants and vulnerable, endangered, or invertebrates. At least 33 British Red Data Book invertebrates critically endangered species and at least eight British Red Data Book plants are represented or threatened ecological on site. communities) Criterion 5 (It regularly Winter counts over five years (1998/99–2002/03) recorded a supports 20,000 or more peak mean of 51,343 waterfowl in the Solent and Southampton waterbirds) Water Ramsar site.

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Criteria Detail Criterion 6 (It regularly The following qualifying species/populations (as identified at supports 1% of the designation) are recorded on the Ramsar Information Sheet: individuals in a population of Spring/autumn peak counts: one species or subspecies Ringed Plover Charaduris hiaticula 397 individuals, average of of waterbird) 1.2% of GB population (5 year peak mean 1998/9–2002/3) Winter peak counts: Dark-bellied Brent Goose Branta bernicla 6456 individuals, representing an average of 3% of the population (5 year peak mean 1998/9–2002/3) Eurasian Teal Anas crecca 5514 individuals, representing an average of 1.3% of the population (5 year peak mean 1998/9– 2002/3) Black-tailed godwit Limosa limosa islandica 1240 individuals, representing an average of 3.5% of the population (5 year peak mean 1998/9–2002/3 Source: JNCC website: http://jncc.defra.gov.uk/pdf/RIS/UK11063.pdf D2.4.1.2 Assessment While Ramsar sites are not part of the Natura 2000 network, they are considered as such for the Habitats Directive and Habitats Regulations Assessment process.

These assessments suggest that although there is a minor theoretical pathway for the impact of low river flows, the waterbirds and wetland habitats identified here would have been exposed to severe drought conditions prior to implementation of the drought orders. The drought orders will not affect the tidal regime or elicit significant impacts on salinity gradients that could trigger a significant impact pathway.

Taking these considerations into account, the incremental impact of the drought orders beyond that of the prevailing drought conditions is not likely to have a significant effect on the qualifying features of the Solent and Southampton Water Ramsar site. D.2.5. Sites of Special Scientific Interest D.2.5.1. River Itchen SSSI D.2.5.1.1. Baseline

Notified features The River Itchen is designated along much of its length as a SSSI. Natural England’s Designated Sites View website40 provides a list of notified features which have been grouped into eight categories:

 Flowing Waters - Type III: Base-Rich, Low-Energy Lowland Rivers and Streams, generally with a stable flow regime  Fish, specifically: - Atlantic Salmon, Salmo salar - Brook Lamprey, Lampetra planeri - Bullhead, Cottus gobio

40Natural England, Designated Sites View website https://designatedsites.naturalengland.org.uk/SearchRegion.aspx, accessed February 2017

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 Invertebrate assemblage including specifically: - White-clawed crayfish, Austropotamobius pallipes - Nationally rare and scarce dragonfly species including the Southern damselfly Coenagrion mercuriale  Mammals, specifically: - Otter, Lutra lutra - Water Vole, Arvicola terrestris  Assemblages of breeding birds associated with lowland open waters and their margins  Lowland wet grassland and meadow, specifically: - M22 - Juncus subnodulosus - Cirsium palustre fen meadow - MG5 - Cynosurus cristatus - Centaurea nigra grassland - MG8 - Cynosurus cristatus - Caltha palustris grassland  Fen, marsh and swamp, specifically: - S25 - Phragmites australis - Eupatorium cannabinum tall-herb fen - S26 - Phragmites australis - Urtica dioica tall-herb fen - S4 - Phragmites australis swamp and reed-beds - S5 - Glyceria maxima swamp - S7 - Carex acutiformis swamp  Lowland woodland, specifically: - W1 - Salix cinerea - Galium palustre woodland - W5 - Alnus glutinosa - Carex paniculata woodland - W6 - Alnus glutinosa - Urtica dioica woodland

Condition assessment The SSSI Units in the hydrological zone of influence identified in Appendix B of the EAR are shown in Figure 1 and the current Condition Assessment for these units (downloaded February 201740) is shown in Table 9.

Table 9 Condition Assessment for SSSI Units in the hydrological zone of influence of the drought orders Unit Unit name Condition Condition Habitat threat risk Unfavourable - Fen, marsh and swamp - 73 Fen south of M3 Medium Recovering lowland Formerly Unit 2 Unfavourable - 74 Winchester Low Neutral grassland - lowland Recovering Meadows Itchen Farm South Unfavourable - 75 Medium Neutral grassland - lowland of M3 Recovering Unfavourable - 76 Former Unit 14 Medium Neutral grassland - lowland Recovering Woodland West of No identified Broadleaved, mixed and yew 77 Favourable Compton Lock threat woodland - lowland

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Unit Unit name Condition Condition Habitat threat risk Unfavourable - 78 Twyford Meads Low Neutral grassland - lowland Recovering No Unfavourable - Fen, marsh and swamp - 79 79 assessment Declining lowland undertaken Unfavourable - 80 Former Unit 13 Low Neutral grassland - lowland Recovering No Unfavourable - Fen, marsh and swamp - 81 81 assessment Declining lowland undertaken No Manor Farm - Unfavourable - 82 assessment Neutral grassland - lowland Mariner's Meadow No change undertaken Manor Farm - Unfavourable - 83 Medium Neutral grassland - lowland Twyford Moors Recovering Otterbourne Unfavourable - 84 Meadows N of Kiln Medium Neutral grassland - lowland Recovering Lane Otterbourne No Unfavourable - 85 Meadows S of Kiln assessment Neutral grassland - lowland Declining Lane undertaken No Unfavourable - 86 Former Unit 9 assessment Neutral grassland - lowland No change undertaken Middle Itchen No Unfavourable - 107 (Easton to assessment Rivers and streams No change Highbridge) undertaken Lower Itchen No Unfavourable - 108 Highbridge to Wood assessment Rivers and streams No change Mill undertaken M3 (Formerly Part Unfavourable - No identified 128 Neutral grassland - lowland Of Units 82 & 83) Recovering threat Unit 129 (Formerly Unfavourable - No identified Broadleaved, mixed and yew 129 Part Of Unit 107) Recovering threat woodland - lowland 130 (Formerly part No identified Broadleaved, mixed and yew 130 Favourable of unit 107) threat woodland - lowland No Formerly part of unit Unfavourable - Broadleaved, mixed and yew 131 assessment 85 Declining woodland - lowland undertaken Woodland formerly No identified Broadleaved, mixed and yew 132 Favourable part of 86 threat woodland - lowland No Brambridge Unfavourable - 138 assessment Neutral grassland - lowland Meadows Declining undertaken

D.2.5.1.2. Assessment Methodology The assessment for the River Itchen SSSI has been structured to cover the eight categories of notified features set out in Section D.2.5.1.1.

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D.2.5.1.3. Features Assessment

Flowing Waters - Type III: Base-rich, low-energy lowland rivers and streams The riverine SSSI Unit 107 ‘Middle Itchen’ extends from Easton to Highbridge and Unit 108 ‘Lower Itchen’ extends from Highbridge to the downstream limit of the SSSI at Wood Mill. Both these Units have a current Condition Assessment status of ‘unfavourable no change’. The flowing waters – Type iii habitat broadly equates to the SAC notified feature of ‘Water courses of plain to montane levels with the Ranunculion fluitantis and Callitricho-Batrachion vegetation.’ The assessment of mechanisms for potential impacts of the drought orders is therefore the same, underpinned by the extensive studies relating to the RoC Appropriate Assessment that set the Sustainability Reductions for the River Itchen.

On the basis of the earlier SAC assessment, it is anticipated that although mechanisms exist for flow-related impacts on macrophytes and their related communities of the lower Itchen, the infrequency of drought order implementation and speed of recovery following a drought suggest that the drought orders are not likely to damage the type iii chalk stream feature.

Fish including Atlantic salmon (Salmo salar), brook lamprey (Lampetra planeri) and bullhead (Cottus gobio) Each of these species has already been assessed earlier as they are qualifying features for the River Itchen SAC. More detail on the assessment can be found in section D.2.2.1.2 above but the conclusion for the SSSI is that:

 With regard to bullhead and brook lamprey, surveys have shown that both of these fish species occur throughout the catchment in habitats where they would be expected. Both species are also considered to be relatively resilient to environmental stress and hence the implementation of the drought orders is not likely damage these SSSI interest features.  With regard to Atlantic salmon, while data are not available for very low flows, on the basis of the earlier SAC assessment, it is anticipated that while mechanisms may exist for very low flows to impact Atlantic salmon, the magnitude, duration and infrequency of drought order flow impacts suggests that the drought orders are not likely to damage the Atlantic salmon population.

Invertebrate assemblage including: white-clawed crayfish (Austropotamobius pallipes) and the Southern damselfly (Coenagrion mercuriale). The notified features for the River Itchen SSSI covers its broader macroinvertebrate community in addition to specific reference to white-clawed crayfish and the Southern damselfly. As set out in Section D.2.2.1.2, although white-clawed crayfish were assessed as being affected by abstraction, their populations are constrained to the upper catchment and hence not affected by the Lower Itchen and Gaters Mill drought orders.

The impacts on the Southern damselfly have also been assessed earlier in D.2.2.1.2. Based on these considerations, although the implementation of the drought orders will be infrequent and the assessed magnitude of impact on the Southern damselfly is low, adverse effects on the Southern damselfly population cannot be ruled out.

Macroinvertebrate assemblage The macroinvertebrate assemblage is a SSSI interest feature of the River Itchen and is of key importance to the functioning, biodiversity and integrity of the wider chalk stream habitat.

With regard to the broader aquatic macroinvertebrate communities, these are a key indicator of the overall condition of the river including flow requirements. As part of the RoC work, the Environment Agency concluded that reduced river flows were causative in changes in the characteristic chalk

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stream invertebrate community41. Macroinvertebrate communities were shown to be impacted by low flows in the River Itchen, for example over the period from 1989 to 1992, with important species (for example, several mayfly species) showing a significant reduction in abundance. The analysis also indicated that the flow impacts on macroinvertebrates tend to be relatively short-lived, with recovery being rapid once higher flows return.

Baseline A summary of macroinvertebrate monitoring site locations and records of relevance to the Lower Itchen and Gaters Mill sources is presented in Table 10 ordered from upstream to downstream on the River Itchen.

Table 10 Environment Agency macroinvertebrate monitoring sites located within the hydrological zone of influence of the drought orders Site name Monitoring period NGR St Cross Bridge 1991-2016 SU4764027030 Otterbourne Waterworks 1989-2015 SU4706023240 Bishopstoke 1989-2015 SU4665019040 D/S Chickenhall STW 1978-2009 SU4652017380 Gaters Mill 1989-2010 SU4533415628

Work by Exley41 suggests that the monitoring sites at Bishopstoke and Otterbourne have been sampled inconsistently due to deep pools and variable accessibility in the past. While these data therefore may be excluded from hydroecological assessments, they still provide a useful baseline of the species present in the river. Greater emphasis will be given to the results from d/s Chickenhall STW and Gaters Mill when looking at indices and for more incisive hydroecological assessment.

No macroinvertebrate data are available for the reach downstream of Gaters Mill. The reach immediately downstream of Gaters Mill at Riverside Park is highly modified and canalised which is therefore likely to support a much restricted macrophyte community due to morphological as well as hydraulic constraints. The conditions would not be suitable for hydroecological assessment and so no macroinvertebrate monitoring sites are located there. Immediately downstream of Riverside Park is the natural tidal limit of the River Itchen; it is likely that the typically chalk stream community will begin a transition downstream of Riverside Park in favour of a more tidally-influenced, transitional aquatic macroinvertebrate community.

Macroinvertebrate species have typically short life cycles and for many taxa they may have only one aquatic life stage. An understanding of the seasonality of their presence and abundance in the aquatic environment is important in understanding and interpreting macroinvertebrate data.

Many freshwater invertebrates have annual life cycles with adults emerging in spring, giving rise to a short-lived egg phase and larvae that live in freshwater for most of the year. Other invertebrates (such as the freshwater shrimp) have shorter life cycles including several generations per year, and occasionally some taxa live in freshwater for several years. As a result of these different life strategies the composition of invertebrate communities, and indeed the hydroecology of the community, is likely to vary considerably between the seasons. Numbers of individuals within the community can change rapidly with population booms and crashes occurring quite rapidly in response to changing environmental conditions.

41 Exley, K (2005). River Itchen macroinvertebrate community relationship to river flow changes. Environment Agency Report.

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The Environment Agency monitoring programme typically collects macroinvertebrate samples in spring and autumn, with summer samples collected in some years. A proportion of variation between data sets can always be attributed to seasonal variation and also between sites due to their distance from the source due to natural transitions downstream.

A consideration of the species list for sites upstream and downstream of Southern Water’s Lower Itchen sources and upstream of the Gaters Mill abstraction intake indicate a very diverse range of macroinvertebrates with high abundances, typical of a chalk stream macroinvertebrate community. At all sites, the dominant taxa are Baetidae (olive mayfly), Caenidae (anglers curse mayfly), Ephemerellidae (blue winged olive mayfly) and Gammaridae (freshwater shrimp).

Baetidae, Ephemerellidae and Gammaridae are all invertebrates that favour fast-flowing river habitats and dislike silt42. Conversely, the family Caenidae is generally regarded as a low flow tolerant taxon; however in the River Itchen this family is often represented by the species Caenis rivulorum, which prefers fast-flowing water42. These invertebrates are highly characteristic of the typical chalk stream fauna and are often present in very high numbers as seen at all sites in the Lower Itchen.

The lower monitoring sites are characterised by the addition of taxa such as Aphelocheiridae (saucer bug) and Brachycentridae (grannom sedge caddisfly), which are not present above Bishopstoke. In the lower reaches of the river, these taxa are present in very high abundances.

Assessment - macroinvertebrates In addition to the full species lists, a number of standard macroinvetebrate community indices are provided with the Environment Agency macroinvertebrate data43 (Table 11):

 Biological Monitoring Working Party (BMWP) is primarily used to monitor the impact of organic enrichment, but also responds to toxic pollution, siltation, habitat reduction and reduced flows. High BMWP scores are associated with good water quality and high habitat quality. BMWP scores cannot be directly compared across river types. A high BMWP score in an upland stream might be 70, where as a high score in a Chalk stream could be upwards of 250.  Number of Scoring Taxa (NTAXA) is a simple species richness index. It is simply the number of scoring taxa (families) that contributed to the BMWP score. Habitat-rich rivers, such as lowland Chalk streams, will often have NTAXA scores exceeding 30. Upland systems with restricted habitats tend to have lower values. River reaches with impoverished habitat quality, siltation issues or reduced water quality will typically have reduced NTAXA scores compared with less impacted reaches in similar river types.  Average Score Per Taxon (ASPT) is the BMWP divided by NTAXA, and is less influenced by seasonal community changes. ASPT is the most appropriate index of the three ‘traditional’ community metrics by which to monitor a site over time. Broadly speaking, ASPT scores of 5 and above are considered to represent invertebrate communities associated with good water quality. Lower scores are indicative of invertebrate communities associated with poor water quality.  Lotic invertebrate Index for Flow Evaluation (LIFE) was developed as a means of assessing flow as a stressor of the macroinvertebrate community of flowing watercourses. Individual species and family groups are assigned to a flow group depending on their documented flow

42 Extence, C.A., Balbi, D.M. and Chadd, R.P. (1999) River flow indexing using British benthic macroinvertebrates: A framework for setting hydroecological objectives. Regulated Rivers: Research and Management 15, 543-574 43 Chadd, R.P. and Extence, C.A. (2004) The conservation of freshwater macroinvertebrate populations: a community-based classification scheme. Aquatic Conservation: Marine and Freshwater Ecosystems.14, 597–624.

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preferences (flow velocity) ranging from I (Rapid) to VI (Drought Resistant). Species LIFE (S) provides a more precise measure than Family LIFE (F) as a number of aquatic invertebrate families contain species with wide-ranging flow requirements. The community LIFE score can be broadly interpreted according to published thresholds, ranging from 6.5 and below (Low sensitivity to reduced flows) to 7.26 and above (High sensitivity to reduced flows).  Community Conservation Index (CCI) provides a measure of overall community conservation value, and highlights specific species of conservation importance based on JNCC threat categories (after Wallace, 199144). CCI can be broadly interpreted according to published thresholds, ranging from a score of <5 (Low conservation value- sites supporting only common species and/or a community of low taxon richness) to >20 (Very High conservation value- sites supporting several rarities, including species of national importance, or at least one extreme rarity). Macroinvertebrate communities are made up of many often short-lived taxa which may spend only part of their life cycle in the aquatic environment. There is a typical transition of species downstream in any watercourse and a seasonal variability based on the life cycles of the taxa present. The natural variability between sites and between seasons should always be borne in mind when considering macroinvertebrate data.

Table 11 Macroinvertebrate monitoring: community indices BMWP NTAXA ASPT LIFE (F) LIFE (S) CCI St Cross MEAN 215 35 5.85 7.16 7.26 23.99 MIN 149 25 5.51 6.68 5.00 11.15 MAX 297 44 6.22 7.71 7.93 70.00 Otterbourne MEAN 204 33 6.13 7.29 7.59 18.95 MIN 133 22 5.62 6.50 6.00 7.00 MAX 240 41 6.78 7.77 9.00 25.58 Bishopstoke MEAN 210 33 6.36 7.54 7.99 23.88 MIN 139 23 5.96 7.02 7.00 12.30 MAX 261 43 6.97 8.04 8.34 80.00 D/S Chickenhall MEAN 178 32 5.54 6.86 7.39 20.05 MIN 117 23 4.84 6.24 6.97 8.86 MAX 232 40 6.20 7.40 8.00 36.67 Gaters Mill MEAN 184 32 5.67 7.00 7.30 17.90 MIN 103 19 4.97 6.37 6.84 7.00 MAX 228 37 6.36 7.46 10.00 25.74

The mean NTAXA is very similar throughout the river and always greater than 30 which suggests a rich, diverse community as expected in a chalk stream such as the Itchen. The CCI scores are over

44 Wallace, I.D. (1991) A review of the Trichoptera of Great Britain. Research and Survey in Nature Conservation No. 32. Nature Conservancy Council: Peterborough.

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20 at most sites further supporting the assessment of the very high conservation value of the sites based on their macroinvertebrate assemblages.

BMWP and ASPT are high and indicate a strong community living in good water quality. Nevertheless a slight drop in BMWP and ASPT while maintaining NTAXA does suggest water quality may be impacting the sites downstream of Chickenhall.

The mean LIFE scores are more important for assessment of long-term impacts of flow on the macroinvertebrate community. LIFE scores stay high upstream and downstream of Southern Water’s Lower Itchen sources and are high at Gaters Mill; the family score is slightly lower at the ‘d/s Chickenhall’ site. Family level scores are intermediate suggesting the macroinvertebrate community has a number of families which have a preference for high flows and therefore the community may be sensitive to changes in flow. The species level indices are typically higher and, where available, are a better representation of the conditions in the river as there can be differences in flow tolerances and preferences between species of the same family. For example, in this case it appears the greater flow sensitivity at the species level may be a function of the presence of the mayfly Caenis rivulorum.

The family Caenidae is generally regarded as a low flow tolerant taxon; however, in the River Itchen this family is often represented by the species Caenis rivulorum, which prefers fast-flowing water45. This means that at the family level, Caenidae which scores as flow tolerant (low scoring) will result in a lower LIFE(F) score relative to the LIFE(S) score since, at the species level, Caenis rivulorum scores as flow sensitive (high scoring).

Overall the sites upstream and downstream of Southern Water’s Lower Itchen sources do not appear to be flow damaged based on their present assemblages - a range of flow sensitive species are present at all sites suggesting they may be sensitive to low flows should they occur.

River flow relationship to macroinvertebrate communities on the Itchen It is widely accepted that many freshwater invertebrates demonstrate preferences for particular velocities or flow regimes – this may be as a direct result of respiratory or feeding requirements, or indirect habitat determination, and has a direct effect on the composition of the invertebrate assemblage at a given site. Of course, many other abiotic and biotic factors will be influencing the invertebrate community in addition to the flow regime, for example: water quality, temperature, weed management, predation and competition.

The understanding of the links between prevailing river flow conditions and invertebrate community variation (including an assessment of the flow preferences of all freshwater invertebrates) is widely used in the application of the LIFE index, as described above. More detail on the development of this index is provided in the publication on the LIFE technique45.

Assessments made as part of the RISS Study46 concluded that, in line with the established relationship, the composition of the invertebrate community and the abundance of key chalk stream taxa within the River Itchen were associated with variations in river flow.

Examining community level macroinvertebrate data provides a good representation of ecosystem status, and is of great relevance to the SSSI designation. A detailed study by Exley47 focused primarily on the relationship between flow and macroinvertebrate community composition.

45 Extence, C.A., Balbi, D.M. and Chadd, R.P. (1999) River flow indexing using British benthic macroinvertebrates: A framework for setting hydroecological objectives. Regulated Rivers: Research and Management 15, 543-574 46 Environment Agency (2004) River Itchen Sustainability Study, November 2004 47 Exley, K (2005). River Itchen macroinvertebrate community relationship to river flow changes. Environment Agency Report.

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Community changes were observed related to changes in flow in the river. The hypothesised mechanism through which the macroinvertebrate community (LIFE scores) are linked to flow is largely through sensitivity to water velocity and siltation, driven by flow variability at sites with fixed channel dimensions48.

The data analysis showed that the macroinvertebrate community present in spring, as represented by the LIFE scores, was most frequently driven by the antecedent summer low flows, as represented by the summer Q95. This is consistent with the findings of Extence et al.48 who found that the previous summer flow was a primary factor influencing chalk stream invertebrate communities. It was also noted that summer average flows and winter average and high flows were also strongly related to invertebrate community variationError! Bookmark not defined..

Under low flows, the macroinvertebrate community of all sites had lower LIFE scores and therefore potentially exhibited hydro-ecological stress.

While the shift in community is important, it is also important to understand which taxa are responsible for this community shift to understand the ecological significance of the change. An analysis of the taxonomic changes in the community showed that the score changes were driven by the drop in abundance of key dominant flow-loving tax rather than the gain in abundance of slow flow-loving taxa. Samples below the flow threshold contained a much lower abundance of many chalk stream and fast flow preference taxa but in particular of Baetidae (olive mayfly), Caenidae (anglers curse mayfly – largely the fast flow loving Caenis rivulorum), Ephemerellidae (blue winged olive mayfly) and Gammaridae (freshwater shrimp). These macroinvertebrates are highly characteristic of the typical chalk stream fauna and may be considered as a negative change in this context. The implications of the community change have already been considered in the assessment of impacts on the salmon population (in particular in section D.2.2.1.2 above).

Thresholds for impact were identified based on the work by ExleyError! Bookmark not defined. and there are a number of key points to consider in relation to the use of these thresholds:

 Ecological stress related to low flows can occur naturally in the absence of abstraction impacts and may be beneficial to some aspects of the ecosystem.  Flow thresholds presented in the Exley work represent a point of ecological stress related to low river flows and not damage related to abstraction impacts.  In order to determine the impacts of abstraction, there is a need to consider the frequency, duration and extent by which the presented flow thresholds are exceeded under different flow (abstraction) scenarios – see further information on this below  Evidence from the River Itchen over the last 16 years or so suggests that the macroinvertebrate community is able to recover rapidly and fully from the impacts of low flows once higher flows return. The impacts of a dry summer will be limited to one year assuming that flows in the following summer are higherError! Bookmark not defined..

Application of the SAP targets In 2007 the Environment Agency published Site Action Plan (SAP) Targets for the River Itchen which were based on the macroinvertebrate flow relationships discussed above. Table 12 presents the SAP targets identified for the reaches downstream of Southern Water’s Lower Itchen sources.

48 Extence, C.A., Balbi, D.M. and Chadd, R.P. (1999) River flow indexing using British benthic macroinvertebrates: A framework for setting hydroecological objectives. Regulated Rivers: Research and Management 15, 543-574

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Table 12 SAP flow targets downstream of Southern Water's Lower Itchen sources Target Stage 4 Invertebrate Flow Criteria Ml/d Management Unit 5 ref Allbrook and Highbridge 1 Long-term summer Q95 must exceed: 262 Ml/d 2 Flow should not fall below: 198 Ml/d 3 Summer Q95 should not fall below: 237 Ml/d In more than 1:6 years

Based on the current drought plan scenario, Aquator modelling (specifically, Model Run DP0004_f presented in Appendix B of the EAR) has shown that:  Target 1 – mean summer Q95 comfortably exceeds the target of 262 Ml/d, indicating that the long-term flow regime should sustain a healthy invertebrate population.  Target 2 – modelling shows that minimum river flows may fall below the 198 Ml/d HOF at Allbrook and Highbridge once every 130 to 170 years on average. Flows will exceed 198 Ml/d on over 99% of days and will be above 237 Ml/d on over 90% of days. About 0.3% of days may have flows <198 Ml/d, amounting to about 11 days over 2 separate events in the 80- year historic climate sequence.  Target 3 – summer Q95 flows would fall below 237 Ml/d once every 5.8 (stochastic flow sequence) to 7.3 (historic flow sequence) years on average. This is approximately the same as or less than the target frequency. It is misleading to see the s52 licence HOF of 198Ml/d as a benchmark for the long-term health of the river. Summer flows regularly at the 198Ml/d level will not sustain a healthy chalk stream habitat. Conversely if the long-term mean flow targets are consistently met, flows falling below the HOF for a period of time are very unlikely to cause serious or irreversible damage to the chalk stream habitat.

Hydrological and habitat variable impacts of the drought order(s) application The hypothesised mechanism through which the invertebrate community (LIFE scores) are linked to flow is largely through sensitivity to water velocity and siltation49.

Appendix B of the EAR presents indicative calculations of flow velocities experienced in the river with flows at the licence HOFs and the drought order HOFs. While there are a number of uncertainties that need to be borne in mind, the calculations provide a reasonable indication of the sensitivity of velocities and water depths to changes in low flow, and specifically the reduction in flow from the licence HOFs to drought order HOFs for the Lower Itchen. Full details of the method used to derive these estimations and their limitations are presented in Appendix B of the EAR.

The main points to take from the hydrological assessment presented in Appendix B and the habitat variable results are:

 Velocities at all cross-sections change very little from the licence HOFs and the proposed drought order HOFs (never more than 0.04 m/s). At the three cross-sections where velocities are lowest (below 0.3 m/s), the change in velocity between the licence HOFs and the proposed drought order HOFs is very small (0.01 to 0.02 m/s).  Water depths at all cross-sections are maintained above 0.4 m and unlikely to be limiting to macroinvertebrate assemblages.

49 Exley K. (2006) River Itchen Macro-Invertebrate Community Relationship To River Flow Changes, Environment Agency Report, October 2006

37 Appendix D Environmental Features Assessment

 Information presented in Appendix B provides an initial understanding as to the likely scale and frequency of flow impacts associated with the drought orders under historical climate conditions (1918 – 1997). The analysis illustrates that neither the Lower Itchen sources nor the Gaters Mill drought orders would have been required under the historical climatic conditions examined as neither the Allbrook & Highbridge or Riverside Park HOFs are breached.  To look at drought severities greater than those experienced in the historical record requires the use of stochastic time series. Analysis of the stochastic time series indicates that the frequency with which the drought orders would be needed below the licence HOFs of 198 Ml/d and 194 Ml/d is approximately 1 in 130 to 1 in 170 years. This assumes that the Testwood and Candover Augmentation Scheme Drought Orders have already been implemented. This suggests that in the Lower Itchen the macroinvertebrate community will only be put under flow-related stress very infrequently and the velocity changes as a result of the flow change is minimal beyond that arising due to the prevailing drought conditions without the drought orders in place.

Summary - macroinvertebrate assemblage Baseline

 Five Environment Agency macroinvertebrate monitoring locations on the Lower Itchen from St Cross Bridge (upstream of the Otterbourne abstraction) to upstream of Gaters Mill indicate a very diverse range of macroinvertebrates with high abundances of key taxa, which is typical of a chalk stream macroinvertebrate community.  At all sites, high numbers of the dominant taxa are the fast flow loving, silt intolerant Baetidae (olive mayfly), Caenidae (anglers curse mayfly – Caenis rivulorum), Ephemerellidae (blue winged olive mayfly) and Gammaridae (freshwater shrimp).  No macroinvertebrate data are available for the reach downstream of Gaters Mill. The reach immediately downstream of Gaters Mill at Riverside Park is highly modified and canalised and is therefore likely to support a much restricted macroinvertebrate community due to morphological as well as hydraulic constraints. Immediately downstream of Riverside Park is the natural tidal limit and it is likely that the typically chalk stream community will begin a transition downstream of Riverside Park in favour of a more tidally-influenced, transitional aquatic macroinvertebrate community. Flow relationship with macroinvertebrate communities

 It is widely accepted that freshwater macroinvertebrates demonstrate preferences for particular flows (largely through sensitivity to flow velocities and siltation) affecting the composition of the macroinvertebrate assemblage at any given site. This has been developed into the application of a Lotic Invertebrate Index for Flow Evaluation (LIFE index)50.  Local assessments by the Environment Agency51 concluded that the composition of the Itchen macroinvertebrate community is associated with variations in river flow. A trend was identified linking macroinvertebrate community variation and antecedent summer Q95 flows52.

50 Extence, C.A., Balbi, D.M. and Chadd, R.P. (1999) River flow indexing using British benthic macroinvertebrates: A framework for setting hydroecological objectives. Regulated Rivers: Research and Management 15, 543-574 51 Environment Agency (2004) River Itchen Sustainability Study, November 2004 52 Exley K. (2006) River Itchen Macro-Invertebrate Community Relationship To River Flow Changes, Environment Agency Report, October 2006

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 The community shift was primarily caused by a reduction in the abundance of macroinvertebrates that are highly characteristic of the typical chalk stream community, particularly: Baetidae (olive mayfly); Caenidae (anglers curse mayfly – largely the fast flow loving Caenis rivulorum); Ephemerellidae (blue winged olive mayfly); and Gammaridae (freshwater shrimp). SAP targets

 In 2007 the Environment Agency published SAP targets for the River Itchen which were based on the macroinvertebrate flow relationships discussed above. For the reaches downstream of Otterbourne, the SAP targets were identified as below: - Long-term summer Q95 must exceed 262 Ml/d - Flow should not fall below 198 Ml/d - Summer Q95 should not fall below 237 Ml/d in more than 1:6 years  Based on the current drought plan scenario, Aquator modelling of the proposed drought orders has shown that targets one and three are exceeded indicating that the long-term flow regime should sustain a healthy macroinvertebrate population.  Target two – the 198 Ml/d HOF at Allbrook & Highbridge would not have been breached under the historical climatic conditions examined (1918-1997) and so drought orders would not have been required. The same is true for the Riverside Park HOF.  Stochastic time series were used to look at drought severities greater than those experienced in the historical record. The stochastic time series data show that the Lower Itchen sources and Gaters Mill drought orders are anticipated to be required very rarely. Hydrological and habitat variable impacts of the drought orders

 The hypothesised mechanism through which the macroinvertebrate community (LIFE scores) are linked to flow is largely through sensitivity to water velocity and siltation53. During the extreme conditions when a drought order may be implemented due to the licence HOF being breached: - Velocities at all cross-sections change very little from the existing HOF and the proposed drought order HOFs (never more than 0.04 m/s). At the three cross-sections where velocities are lowest (below 0.3 m/s), the change in velocity between the existing HOF and the proposed drought order HOFs is very small (0.01 to 0.02 m/s). - Water depths at all cross-sections are maintained above 0.4 m and unlikely to be limiting to macroinvertebrate assemblages.  Evidence from the River Itchen over the last 16 years or so suggests that the macroinvertebrate community is able to recover rapidly from the impacts of low flows once higher flows return. The impacts of a dry summer will be limited to one year assuming that flows in the following summer are higher53. Due to the identified low frequency of application of the drought orders, the small magnitude of the velocity changes and the recoverability of macroinvertebrate communities, the incremental impact of the drought orders beyond that of the prevailing drought conditions is anticipated to be small and not likely to damage the macroinvertebrate community.

53 Exley K. (2006) River Itchen Macro-Invertebrate Community Relationship To River Flow Changes, Environment Agency Report, October 2006.

39 Appendix D Environmental Features Assessment

Mammals, specifically: Otter (Lutra lutra) and Water Vole (Arvicola terrestris) Potential impacts on otter populations have been considered earlier in Section 2.2.1.3 and it is considered that implementation of the drought orders are not likely to damage the otter populations.

Water vole can be impacted by dramatic fluctuations in water level and are particularly sensitive to habitat disturbance. Exacerbation of low flows could potentially affect water voles by reducing supporting habitat – but this effect is assessed as minor and the implementation of the drought orders is so infrequent and the impacts on supporting habitats sufficiently small and short-lived that the drought orders are not likely to damage the water vole population in the affected reaches of the River Itchen.

Assemblages of breeding birds associated with lowland open waters and their margins The River Itchen is notified for its assemblage of: (a) breeding birds including: tufted duck Aythya fuligula; pochard A. farina; shoveler Anas clypeata; (b) wading birds: lapwing Vanellus vanellus; redshank Tringa tetanus; snipe Gallinago gallinago; (c) wetland passerines including sedge warbler Acrocephalus schoenobaenus, reed warbler A. scirpaceus and Cetti's warbler Cettia cettia.

Breeding waders, including the notified species of redshank, lapwing and snipe, have undergone a catastrophic decline throughout the floodplains and wet grassland habitats of England. Surveys of this group of birds within the Test and Itchen Valleys have shown a decline that started in the late 1970s and continued into the late 1990s. By the turn of the 21st century, breeding waders were functionally extinct in the Itchen Valley54. Work undertaken in the Itchen Valley as part of the Itchen Sustainability Study55 and the Lower Test Phase 1 Project Report56 identified breeding water bird populations as being particularly sensitive to reduction in floodplain wetness and unfavourable drainage and water level management.

Although there is a pathway for impact, the wading birds, and other birds identified here, would have been exposed to severe drought conditions prior to implementation of the drought orders (on the very rare occasions when they will be required). Operation of the drought orders during prevailing drought conditions is unlikely to impact waders significantly more than the prevailing drought conditions alone as the breeding and feeding resources are likely to already be impacted by the drought conditions. At the end of a drought, when significant rainfall occurs, the recovery of floodplain wetness tends to be rapid. Taking these considerations into account suggests that the incremental impact of the drought orders beyond that of the prevailing drought conditions is not likely to damage the designated bird assemblages.

Fen, marsh and swamp This group comprises the following notified communities:

 S25 - Phragmites australis - Eupatorium cannabinum tall-herb fen  S26 - Phragmites australis - Urtica dioica tall-herb fen  S4 - Phragmites australis swamp and reed-beds  S5 - Glyceria maxima swamp  S7 - Carex acutiformis swamp As for the wading bird assemblages, the key hydrological parameter that could affect these communities is floodplain wetness. In addition, these communities can be significantly affected by

54 Environment Agency (2016) Renewal of the Candover Scheme Abstraction Licence:Part 2 – Environmental Sustainability. 55 Environment Agency (2004) River Itchen Sustainability Study, November 2004 56 Environment Agency (2010) Lower Test Project Report, Phase 1, Testwood Public Water Supply Abstraction Impact Investigation – Statement of Issues and Assessment.

40 Appendix D Environmental Features Assessment

unfavourable management, including water level management. For the same reasons identified for the designated bird features, the incremental impact of the drought orders beyond that of the prevailing drought conditions is not likely to damage the above fen and swamp communities.

Lowland wet grassland and meadow The notified communities considered as part of this group are:

 M22 - Juncus subnodulosus - Cirsium palustre fen meadow  MG5 - Cynosurus cristatus - Centaurea nigra grassland  MG8 - Cynosurus cristatus - Caltha palustris grassland These communities are slightly less sensitive to low wetland water tables than the preceding group57. The same considerations apply and the incremental impact of the drought orders beyond that of the prevailing drought conditions is not likely to damage the fen meadow and grassland communities.

Lowland woodland The notified habitats under this group are:

 W1 - Salix cinerea - Galium palustre woodland  W5 - Alnus glutinosa - Carex paniculata woodland  W6 - Alnus glutinosa - Urtica dioica woodland These are less dependent on high floodplain water tables than the preceding two groups and the drought orders are not likely to damage the woodland communities.

57 Wheeler B.D., Gowing D.J.G.,. Shaw S.C,. Mountford J.O, and Money R.P., (2004). Ecohydrological Guidelines for Lowland Wetland Plant Communities (Eds. A.W. Brooks, P.V. Jose, and M.I. Whiteman,). Environment Agency (Anglian Region)

41 Appendix D Environmental Features Assessment

D3. Ecological community assessment and WFD assessment For the purpose of the environmental assessment, the ecological valuation of fish, macrophyte and macroinvertebrate communities on the River Itchen is ultimately dictated by their status as SAC qualifying features and/or SSSI notified features supporting the River Itchen SAC and SSSI.

The ecological valuation and source-pathway-receptor model of impact assessment is unchanged whether assessing ecological impacts in relation to the River Itchen SAC, or an underlying WFD water body. The ecological communities are the same, albeit they are described differently under each reporting framework. For example, the WFD classification has a community level focus whereas SAC / SSSI designation also has a species-specific context.

The potential WFD outcome of a given ecological impact is relevant, and may vary spatially subject to the delineation of WFD water body extents and the existing classification of WFD sub-elements.

The impact assessment outlined in Section D2 (Designated Sites) is therefore not repeated in full here in relation to WFD biological quality elements on the River Itchen. Rather, impacts identified within Section D2 are given context in relation to WFD water bodies, with a summary of recent available WFD monitoring data.

The WFD surface water bodies that are located within the hydrological zone of influence of the Lower Itchen drought orders are the Itchen (GB107042022580) and Southampton Water (GB520704202800). Summary River Basin Management Plan (RBMP) data relating to the overall ecological status of each water body is presented in Table 13 and Table 14. Note that ecological status is combined with a chemical status assessment (based on priority substances and other pollutants with EU environmental quality standards) to determine the overall surface water body status for River Basin Management Plan (RBMP) reporting. Overall water body assessments are not reproduced here.

Table 13 Summary WFD RBMP classification data for surface water bodies Water body ID GB107042022580 Water body Name Itchen RBMP Cycle 2 Overall Ecology Good Status/Potential: Fish High Macroinvertebrates High Macrophytes and Phytobenthos High Physico-chemical elements High Hydro-morphological quality Supports Good elements Specific pollutants High Hydro-morphology designations: Not designated artificial or heavily modified

RBMP2 water body objective Overall n/a (2027): Fish n/a Macroinvertebrates n/a Macrophytes and Phytobenthos n/a

42 Appendix D Environmental Features Assessment

Table 14 Summary WFD RBMP classification data for transitional water bodies Water body ID GB520704202800 Water body Name Southampton Water RBMP cycle 2 Overall ecology Moderate Status/potential Fish Good Macroinvertebrates Good Macroalgae Good Physico-chemical elements Moderate Hydromorphological quality Supports good elements – Heavily modified Specific pollutants High RBMP2 water body objective Overall Moderate (2027) Fish Good Macroinvertebrates Good Macroalgae Good

D 3.3 Itchen Water body (GB107042022580) D.3.3.1. Macrophytes D.3.3.1.1. Baseline The assessment of River Itchen SAC and SSSI qualifying features and conservation objectives identified potential impacts to macrophyte communities and therefore risks to the WFD macrophyte biological quality element for WFD water bodies due to the drought orders.

Available macrophyte data (2002-present) from Environment Agency macrophyte monitoring locations have been identified for the Itchen water body. A summary of the monitoring site locations and records is presented in Table 15, ordered from upstream to downstream on the Itchen.

Table 15 Environment Agency macrophyte monitoring sites located within the hydrological zone of influence Site name Site ID Monitoring NGR WFD water body Water body period (no macrophyte of and samples) phytobenthos combined classification St Cross 43091 2010-2016 SU4764027030 GB107042022580 High Bridge (2) Itchen Section 19 110184 2004-2009 SU4761024450 (D/S Norris's Bridge) Section 21 110201 2003-2009 SU4659021540 (U/S Highbridge) Section 22 110202 2002-2009 SU4684021060 (D/S Highbridge)

43 Appendix D Environmental Features Assessment

Site name Site ID Monitoring NGR WFD water body Water body period (no macrophyte of and samples) phytobenthos combined classification Section 23 133641 2002-2009 SU4607020580 (Stoke Common) Section 25 110203 2002-2010 SU4663018670 (U/S Bishopstoke) Section 26 110207 2002-2009 SU4676017780 (Chickenhall, U/S Railway) Section 27 110246 2002-2010 SU4636017230 (Chickenhall, D/S Railway) Section 28 110222 2004-2009 SU4536015640 (U/S Gaters Mill) N/A N/A Bow Lake N/A GB107042016650 Good stream Bow Lake

A number of standard community metrics were provided with the Environment Agency macrophyte data: the River Macrophyte Hydraulic Index (RMHI); the River Macrophyte Nutrient Index (RMNI); the Number of Macrophyte Taxa (NaTAXA); and the Number of Functional Groups (NFG) (UKTAG, 201458):

 RMHI describes community preference for flow conditions on a scale of 1 to 10. A score of 10 would indicate a plant community that has a preference for very slow flow or no-flow conditions, while scores of 1 are found in plant communities with a preference for very fast flows;  RMNI is designed to categorise macrophyte community preference to nutrient levels. Scores range from 1 to 10 with scores of 1 representing plant communities with preference for very low levels of nutrients and 10 representing communities with a preference for very enriched conditions;  NaTAXA is a community richness index and simply describes the number of truly aquatic taxa present. Higher values represent a more diverse and rich aquatic plant community;  NFG is another richness/diversity index and describes the number of functional macrophyte groups existing within a surveyed plant community. Twenty-four different functional groups (FG) have been defined. The higher the NFG value, the more diverse and rich the plant community is considered to be. Only taxa that are obligate hydrophytes (i.e. truly aquatic) are assigned scores under the NaTAXA and NFG scoring systems. With the exception of RMHI, these metrics are currently used in biological site classification under the WFD. An additional algal coverage metric (ALG, which provides a

58 UKTAG (2014). UKTAG River Assessment Method Macrophytes and Phytobenthos (River LEAFPACS 2), July 2014. ISBN: 978-1-906934-44-6

44 Appendix D Environmental Features Assessment

percentage coverage of green filamentous algae and ranges from 0-100) is used to support biological site classifications under the WFD. However ALG data were not provided.

Cumulatively, the Itchen macrophyte monitoring points can be used to provide an indicative WFD water body based classification of community environmental preferences, and therefore sensitivity to potential environmental pressures associated with the drought orders.

Table 16 provides a summary of reach-based indices. Combining individual monitoring points to a reach-based index risks generating mean values that do not truly reflect a specific community present within the reach (for example if two vastly different macrophyte communities were amalgamated). Equally, the mean index value for the reach does not necessarily reflect the range of communities present. The inclusion of minimum and maximum values for each index in Table 16 provides an indication of this range and therefore the validity of the reach-based mean index value.

Although there is significant variation in NFG and NaTaxa recorded across sample sites, these indices are more readily influenced by a range of abiotic factors (e.g. shading, weed management and grazing) that can alter communities directly (through removal) and indirectly (through reduced habitat availability). The RMNI and RMHI provide community level scores which account for variation in the number of taxa recorded, providing a robust classification of the overall flow and nutrient preference of the community. The range apparent within RMNI and RMHI is negligible despite the high number of monitoring points that comprise the sample sets used. This provides confidence that the reach-based mean values presented are meaningful in terms of summarising macrophyte community characteristics at a reach scale.

Mean RMNI values suggest that both reaches support communities that are adapted to mesotrophic (moderate) to eutrophic (high) nutrient conditions.

Mean RMHI values suggest that both reaches support communities that are adapted to low to moderate flow velocities.

Table 16 Environment Agency macrophyte monitoring sites: summary of community indices within the hydrological zone of influence RMNI RMHI NFG NaTAXA Upstream of Otterbourne MEAN 7.59 7.58 6.75 13.25 MIN 7.23 7.22 6.00 10.00 MAX 7.85 7.93 8.00 16.00 Downstream of Otterbourne MEAN 7.80 7.75 8.09 12.59 MIN 6.89 7.04 5.00 6.00 MAX 8.20 8.19 13.00 22.00

D.3.3.1.2. Assessment  In drought conditions macrophyte communities and species can adapt to the prevailing flow conditions and readily change back when conditions revert.  The reach RMHI and RMNI values presented indicate that the macrophyte community on the Itchen is adapted to low-moderate flow and moderate-high nutrient conditions and a wholesale community shift as a result of the implementation of the drought orders is unlikely.  No baseline data exist for the reaches downstream of Gaters Mill but the water body ends just 1 km downstream of the Portsmouth Water abstraction intake.

45 Appendix D Environmental Features Assessment

 A keystone species of the macrophyte community is Ranunculus penicillatus ssp. Pseudofluitans.  Well established optimum and acceptable velocity bands have been identified from a range of literature and research sources giving acceptable velocities for Ranunculus sp. growth between 0.1-0.3m/s and optimal conditions between 0.3-0.5 m/s. Above 0.5 m/s growth is sub-optimal and plants may be susceptible to damage.  Indicative calculations of velocities based on flow conditions in the river suggest that all but three river cross-sections studied downstream of Otterbourne are estimated to be above 0.3 m/s both for the licence HOFs and the proposed drought order HOFs. At the three cross- sections where velocities are estimated to be below 0.3 m/s, the velocity was still in the upper end of the acceptable range.  The change in velocity between the licence HOFs and the proposed drought order HOFs is very small (0.01 to 0.02 m/s).  Historic records show that implementation of the drought orders would be required very rarely on the Lower Itchen. Neither the Allbrook & Highbridge nor the Riverside Park HOFs are breached during the historical climate conditions (1918 – 1997). The stochastic time series for Allbrook & Highbridge and Riverside Park show that the Lower Itchen sources and Gaters Mill drought orders would only be required during drought severities of approximately 1:150 years or higher. The risk of a deterioration in the High status of the macrophyte classification in the Itchen WFD water body (GB107042022580) as a result of the implementation of the drought orders in the Lower Itchen is low in the short term for interim classification and within the longer term reporting cycle of the WFD.

D.3.3.2. Diatoms D.3.3.2.1. Baseline The assessment of River Itchen SAC and SSSI qualifying features and conservation objectives identified the potential for impacts to macrophyte communities. Diatom communities can be affected by similar mechanisms to macrophyte communities (e.g. sedimentation), but are particularly influenced by phosphate levels, specifically soluble reactive phosphorus. The drought orders have been shown to pose a low risk of potential increases in soluble reactive phosphorus throughout all reaches identified within the hydrological zone of influence. Consequently, there is a small potential for impacts on diatom communities associated with implementation of the drought orders.

It should be noted that, although diatom communities comprise part of the overall WFD macrophyte and phytobenthos combined classification in WFD reporting, in high alkalinity rivers such as the River Itchen, diatom classification can be unreliable. The macrophyte classification typically provides a lower status assessment and is therefore often used to dictate the overall status assessment for this element in high alkalinity rivers.

A summary of WFD diatom monitoring site locations and records is presented in Table 17, ordered from upstream to downstream on the Itchen.

46 Appendix D Environmental Features Assessment

Table 17 Environment Agency diatom monitoring sites located within the hydrological zone of influence Site name Site ID Monitoring NGR WFD water body Water body period (no macrophyte of and samples) phytobenthos combined classification St Cross 43091 2010 SU4764027030 GB107042022580 High Bridge (2) Itchen Section 25 110203 2008-2010 SU4663018670 (U/S (3) Bishopstoke) Section 26 110207 2009 SU4676017780 (Chickenhall, (1) U/S Railway) Section 27 110246 2008- 2010 SU4636017230 (Chickenhall, (2) D/S Railway) Gaters Mill 43100 2007-2010 SU4533415628 (4) N/A N/A Bow Lake N/A GB107042016650 Good stream Bow Lake The metric used to classify phytobenthos in rivers is the Trophic Diatom Index (TDI)59; diatom taxa are each assigned a score from 1 (nutrient sensitive) to 5 (nutrient tolerant) and the computed TDI community score range from 0 (very low nutrients) to 100 (very high nutrients). No official TDI data were provided with the Environment Agency data. For the purpose of this assessment, TDI was calculated based on application of the TDI method, although this should be used as indicative only in the absence of official Environment Agency TDI data.

Based on taxa abundance at each monitoring point, TDI was calculated and summarised to provide mean, maximum, and minimum values within the hydrological zone of influence. The results of this exercise are presented in Table 18.

Table 18 Environment Agency diatom monitoring sites: summary of TDI within the hydrological zone of influence TDI Interpretation Upstream Otterbourne MEAN 59 Community adapted to moderate-high nutrient MIN 52 conditions MAX 66 Downstream Otterbourne MEAN 66 Community adapted to moderate-high nutrient MIN 55 conditions MAX 80

59 UKTAG (2014). UKTAG River Assessment Method Macrophytes and Phytobenthos (Phytobethos – Diatoms for Assessing River and Lake Ecological Quality; River DARLEQ2), July 2014. ISBN: 978-1-906934- 42-2.

47 Appendix D Environmental Features Assessment

The mean and range of TDI community scores within each reach suggest the community is adapted to moderate-high nutrient conditions (which accords with the macrophyte assessment). There is evidence of increased nutrient tolerance in the lower reach (Reach B-C) which is intuitive but may be compromised by the low number of monitoring points within Reach A-B. Both the minimum and maximum score within Reach B-C were recorded at different years on the same sample site (upstream of Bishopstoke), suggesting a historical degree of significant nutrient fluctuation at this location, from which there has been recovery (TDI decreases over time at this location, with sequentially lower TDI scores across 3 sampling points in time). The soluble reactive phosphorus monitoring data for Bishopstoke (presented in Appendix B of the EAR) show a general improving trend between 2005 and 2016.

D.3.3.2.2. Assessment Reach TDI values presented indicate that, in general, the diatom community on the Itchen is adapted to moderate-high nutrient conditions. This suggests that the drought orders are unlikely to elicit a wholesale community shift within the Itchen as the community is already adapted to conditions that may be exacerbated by the drought orders (nutrient concentration). However, there remains significant potential for deterioration of the existing community, and changes in the local abundance and distribution of diatom taxa within the wider community present.

From a WFD perspective, given the tolerance of the diatom community present and the uncertainty in diatom classification use in high alkalinity rivers such as the Itchen, it is considered unlikely that any status shift in the Macrophyte and Phytobenthos combined classification would arise from direct impacts of the drought orders on the diatom community in the Itchen water body.

Based on the infrequent use of the drought orders and the low risk to deterioration in nutrient concentrations, it is considered that there is a low risk of deterioration in the ecological status based on the diatoms.

D.3.3.3. Freshwater macroinvertebrates D.3.3.3.1. Baseline Available macroinvertebrate data (2006-present) from Environment Agency macroinvertebrate monitoring locations has been mapped to the Itchen WFD water body. Data are available for five sites in total; no data are available downstream of Gaters Mill. A summary of monitoring site locations and records is presented in Table 19 ordered from upstream to downstream on the Itchen.

Table 19 Environment Agency macroinvertebrate monitoring sites located within the hydrological zone of influence Site name Site Monitoring NGR WFD water Water body ID period (n) body macroinvertebrate classification St Cross 43091 2006-2016 SU4764027030 GB107042022580 High Bridge (11) Itchen

Otterbourne 42048 2006-2015 SU4706023240 Waterworks (18) Bishopstoke 42204 2006-2015 SU4665019040 (19) D/S 43313 2006-2009 SU4652017380 Chickenhall (5) STW

48 Appendix D Environmental Features Assessment

Site name Site Monitoring NGR WFD water Water body ID period (n) body macroinvertebrate classification Gaters Mill 43100 2006-2010 SU4533415628 (7) N/A N/A Bow Lake N/A GB107042016650 Moderate stream Bow Lake

A number of standard community indices were provided with the Environment Agency macroinvertebrate data;

 BMWP is primarily used to monitor the impact of organic enrichment, but also responds to toxic pollution, siltation, habitat reduction and reduced flows. High BMWP scores are associated with good water quality and high habitat quality. BMWP scores cannot be directly compared across river types. A high BMWP score in an upland stream might be 70, where as a high score in a Chalk stream could be upwards of 250. BMWP has recently been replaced by the Whalley, Hawkes, Paisley and Trigg metric (see below).  NTAXA is a simple species richness index. It is simply the number of scoring taxa (families) that contributed to the BMWP score. Habitat-rich rivers, such as lowland Chalk streams will often have NTAXA scores exceeding 30. Upland systems with restricted habitats tend to have lower values. River reaches with impoverished habitat quality, siltation issues or reduced water quality will typically have reduced NTAXA scores compared with less impacted reaches in similar river types.  ASPT is the BMWP divided by NTAXA, and is less influenced by seasonal community changes. ASPT is the most appropriate index of the three ‘traditional’ community metrics by which to monitor a site over time. Broadly speaking, ASPT scores of 5 and above are considered to represent macroinvertebrate communities associated with good water quality. Lower scores are indicative of macroinvertebrate communities associated with poor water quality.  LIFE was developed as a means of assessing flow as a stressor of the macroinvertebrate community of flowing watercourses. Individual species and family groups are assigned to a flow group depending on their documented flow preferences (current velocity) ranging from I (Rapid) to VI (Drought Resistant). Species LIFE (S) provides a more precise measure than Family LIFE (F) as a number of aquatic macroinvertebrate families contain species with wide- ranging flow requirements. The community LIFE score can be broadly interpreted according to published thresholds, ranging from 6.5 and below (Low sensitivity to reduced flows) to 7.26 and above (High sensitivity to reduced flows).  CCI provides a measure of overall community conservation value, and highlights specific species of conservation importance based on JNCC threat categories (after Wallace, 199160). CCI can be broadly interpreted according to published thresholds, ranging from a score of <5 (Low conservation value- sites supporting only common species and/or a community of low taxon richness) to >20 (Very High conservation value- sites supporting several rarities, including species of national importance, or at least one extreme rarity). Of the metrics provided, none are currently used in biological site classifications under the WFD. BMWP (and consequently NTAXA and ASPT) have been superseded by the Whalley, Hawkes,

60 Wallace, I.D. (1991) A review of the Trichoptera of Great Britain. Research and Survey in Nature Conservation No. 32. Nature Conservancy Council: Peterborough.

49 Appendix D Environmental Features Assessment

Paisley and Trigg (WHPT)61 scoring system. WHPT now forms the basis of WFD status classification. WHPT is based on more families than BMWP with a separate value for each abundance category of each taxon, providing increased sensitivity relative to the traditional BMWP method. It also offers better comparability with LIFE and other abundance-weighted indices.

CCI and LIFE have never been used prescriptively for WFD classifications, but support a range of peripheral WFD investigations (for example, in determining whether supporting elements such as hydrology support good ecological status). A further metric useful in this regard, and which would provide valuable information for the assessment of the drought orders, is the Proportion of Sediment- Sensitive Invertebrates (PSI)62 metric. PSI is a biotic index designed to describe a macroinvertebrate community’s sensitivity to sedimentation. It is based on the known ecological responses of different macroinvertebrate species and family groups to the accumulation of sediment on riverine substrate. Sediment transfer and deposition is likely to be affected by the drought orders, and PSI would characterise the baseline sensitivity of the community to this effect.

Cumulatively, the Itchen macroinvertebrate monitoring points can be used to provide an indicative reach-based classification of community environmental preferences (from the metrics available), and therefore sensitivity to potential environmental pressures associated with the drought orders.

Table 20 provides a summary of reach-based indices. Combining individual monitoring points to a reach-based index risks generating mean values that do not truly reflect a specific community present within the reach (for example if two vastly different macroinvertebrate communities were amalgamated). Equally, the mean index value for the reach does not necessarily reflect the range of communities present. The inclusion of minimum and maximum values for each index in Table 20 provides an indication of this range and therefore the validity of the reach-based mean index value.

Table 20 Environment Agency macroinvertebrate monitoring sites: summary of community indices within the hydrological zone of influence BMWP NTAXA ASPT LIFE (S) LIFE (F) CCI Upstream of Otterbourne MEAN 192 32 6.10 7.33 7.69 14.66 MIN 133 22 5.51 6.77 6.00 7.00 MAX 240 40 6.78 7.77 9.00 23.40 Downstream of Otterbourne MEAN 184 30 6.10 7.33 8.00 20.33 MIN 103 19 4.84 6.24 6.84 7.00 MAX 248 39 6.97 8.04 10.00 36.67 There is significant variation across all metrics available meaning it is difficult to comment on general characteristics of each reach. Further analysis of the underpinning data confirms that this significant variability is both spatial and temporal in nature.

Prior to 2008, mean family LIFE scores on the Itchen were below 7.00 (Figure 2); since 2008, mean family LIFE scores have been consistently higher than 7.35 and often higher than 7.50. Similarly, prior to 2008, mean species LIFE scores on the Itchen were below 7.25, and have been consistently

61 WFD-UKTAG (2014), River Assessment Method. Benthic Invertebrate Fauna. Invertebrates (General Degradation): Whalley, Hawkes, Paisley & Trigg (WHPT) metric in River Invertebrate Classification Tool (RICT) UKTAG Method Statement. ISBN: 978-1-906934-62-0. 62 Extence, C.A., Balbi, D.M. and Chadd, R.P. (1999) River flow indexing using British benthic macroinvertebrates: A framework for setting hydroecological objectives. Regulated Rivers: Research and Management 15, 543-574.

50 Appendix D Environmental Features Assessment

higher than 7.90 since 2008. Prior to (and including) 2008, mean ASPT scores were also consistently below 6.00, but have been consistently above 6.00 since 2009.

Figure 2 Temporal variation (mean) of LIFE and ASPT within the hydrological zone of influence (monitoring sites sampled since 2006)

Spatial variability in mean scores is also apparent from the data, with mean family and species LIFE scores, as well as ASPT, consistently lower at the macroinvertebrate site ‘Downstream of Chickenhall STW’ ( Figure 3). This site is associated with a significant river discharge point at the Sewage Treatment Works, which is likely to drive the variation in scores observed at this location.

Combined, these observations suggest that the Itchen macroinvertebrate community in both hydrological reaches can broadly be described as being:

 highly sensitive to reduced flows; and  highly sensitive to organic enrichment and deterioration in water quality. CCI scores (Table 20) also confirm that the River Itchen supports a High (as indicated by mean values) to Very High (as indicated by maximum values) conservation value macroinvertebrate community under the CCI system. The observed CCI scores are driven both by community richness, and the presence of eleven species identified as Regionally Notable63, four species identified as Notable64, and three Red Data Book (RDB) species, namely:  A beetle Graptodytes flavipes (RDB2 (Vulnerable65)): one individual identified at Sewards Bridge in 2015;

63 Species thought to occur in fewer than five localities (regions) across Great Britain. 64 Scarce in Great Britain and thought to occur in less than 100 10km squares of the National Grid. 65 Taxa believed likely to move into the Endangered (RDB1) category in the near future.

51 Appendix D Environmental Features Assessment

 Southern damselfly Coenagrion mercuriale (RDB3 (Rare66)): identified on three occasions at Gaters Mill in 2005 and 2007; and  A caddisfly Erotesis baltica (RDB 3 (Rare28)): one individual identified at Itchen Stoke in 2005.

Figure 3 Spatial variation (mean) of LIFE and ASPT within the hydrological zone of influence (monitoring sites sampled since 2006)

8.50 8.00 7.50 7.00 6.50 6.00 5.50 5.00 ST CROSS OTTERBOURNE BISHOPSTOKE D/S GATERS MILL BRIDGE WATERWORKS CHICKENHALL STW u/s Allbrook & Highbridge d/s Allbrook & Highbridge

MEAN FAMILY LIFE MEAN SPECIES LIFE MEAN ASPT

D.3.3.3.2. Assessment Family and species LIFE scores, as well as ASPT scores (and underpinning BMWP/NTAXA), indicate that, in general, the macroinvertebrate community on the River Itchen is sensitive to reduced flows and deterioration in water quality. The assessment of the impact of the drought orders on these broader communities in the River Itchen has already been covered earlier in the assessment of SSSI macroinvertebrate features.

The hydrological assessment presented in Appendix B of the EAR indicates that under historic flow records, neither the Allbrook & Highbridge nor the Riverside Park licence HOFs are breached during historical climate conditions (1918 – 1997) and the stochastic flow time-series for Allbrook & Highbridge and Riverside Park shows that the Lower Itchen sources and Gaters Mill drought orders would only be required very infrequently.

Scientific understanding is that while macroinvertebrate communities are sensitive to reduced flows, they also recover rapidly and, on the River Itchen, evidence from over the last 16 years or so suggests that the macroinvertebrate community is able to recover rapidly from the impacts of low

66 Taxa with small populations, which are not at present Endangered (RDB1) or Vulnerable (RDB2) but which are at risk.

52 Appendix D Environmental Features Assessment

flows once higher flows return. The impacts of a dry summer will be limited to one year assuming that flows in the following summer are higher67.

No baseline WFD data are available downstream of Gaters Mill with which to characterise the ecological valuation of the macroinvertebrate community for the purpose of assessment. However, just 1km of the water body lies downstream of the Gaters Mill abstraction intake and, as described earlier, the modified river characteristics of this reach are unlikely to support a rich assemblage of macroinvertebrates.

The risk of a deterioration in the High status of the macroinvertebrate classification in the Itchen WFD water body (GB107042022580) as a result of the implementation of the drought orders in the Lower Itchen is low in the short term for interim classification and the longer term reporting cycle of the WFD.

Finally, with regards to the availability of monitoring data, Exley67 assessed the suitability of macroinvertebrate monitoring sites for hydro-ecological analysis. Of the sites in the River Itchen, St Cross Bridge is at the upper limit of the theoretical hydrological zone of influence for the Lower Itchen drought orders and Otterbourne, Bishopstoke, D/S Chickenhall STW and Gaters Mill are within the zone of hydrological influence (see Figure 1 presented earlier). Of these monitoring sites, Exley assessed Otterbourne and Bishopstoke as being unsuitable for analysis (primarily because of their location in pool habitats), with the other three sites assessed as being suitable. Based on data received from the Environment Agency, apart from the St Cross Bridge site, the only other two sites in these reaches where the Environment Agency has continued monitoring since 2010 are Otterbourne and Bishopstoke. The reasons for this are not known but it is a concern that this could limit hydro-ecological analysis of recent and future hydrological events.

D.3.3.4. Freshwater fish D.3.3.4.1. Baseline Environment Agency freshwater fish monitoring data are available for five sites in total from 2006- present in the hydrological zone of influence; no data are available for downstream of Gaters Mill.

A summary of the monitoring site locations and records is presented in Table 21 in order from upstream to downstream on the Itchen.

Table 21 Environment Agency fish monitoring sites located within the hydrological zone of influence Site name Site Monitoring NGR Hydrological WFD water body Water body ID period (n) Reach fish classification Brambridge 30229 2009-2015 SU4676322408 Upstream of GB107042022580 High (2) Otterbourne Itchen Shawford 34565 2008-2015 SU4725324642 Park (6) Segar’s 33949 2009 (1) SU4763924343 Downstream Farm of St Cross 62184 2015 (1) SU4764726965 Otterbourne Bridge Twyford 40070 2011 (1) SU4797925577 Lodge Hockley 33829 2009-2015 SU4803325674 House (2)

67 Exley K. (2006) River Itchen Macro-Invertebrate Community Relationship To River Flow Changes, Environment Agency Report, October 2006.

53 Appendix D Environmental Features Assessment

Lower 34280 2009-2011 SU4673617630 Itchen (2) Fishery – D/S Viaduct Cpue Caravan 30230 2009-2015 SU4683220913 Pool, (2) Highbridge Monitoring sites on the Itchen Navigation have been screened out of this analysis on the basis that Itchen Navigation is an artificial channel with controlled water levels. Sites on the Itchen Navigation are unlikely to provide a suitable baseline for impact assessment, and in more general terms, are unlikely to be affected by flow-related impacts as a result of the drought orders by virtue of being an artificial, level-dependent system.

Species presence and distribution across the monitoring points can be used to provide an indicative reach-based classification of community environmental preferences and therefore sensitivity to potential environmental pressures associated with the drought orders.

Table 22 provides a summary of species presence and distribution across monitoring points, ranked according to species tolerance of environmental disturbance (as defined by the Fisheries Classification Scheme (FCS2)68 used in WFD classifications for the fish biological quality element.

Reach sensitivity can broadly be defined by the most sensitive of the fish taxa present (i.e. those with the lowest tolerance of environmental disturbance):

 The Itchen sites are characterised by a number of species with low tolerance for environmental disturbance, namely the salmonids Atlantic salmon, brown/sea trout and grayling. Of the available monitoring data:

 Shawford Park is used to define the WFD status of the fish biological quality element (alongside two other locations outside of the hydrological zone of influence) and is defined as being of High status under the FCS2 classification (EQR 0.966).

68 UKTAG (2008) Rivers Assessment Methods Fish Fauna (Fisheries Classification Scheme 2 (FCS2)) ISBN: 978-1-906934-09-5

54 Appendix D Environmental Features Assessment

Table 22 Environment Agency fish monitoring sites: summary of species distribution within the hydrological zone of influence WFD water body GB107042022580 Upstream of Allbrook & Highbridge Downstream of Reach Allbrook &

Highbridge

d/s

-

Site name

Brambridge ShawfordPark FarmSegar's Cross BridgeSt TwyfordLodge HockleyHouse Lower Fishery Itchen viaduct CaravanPool, Highbridge

69

Species FCS2 Tolerance to Environmental Disturbance

19/10/2009 02/09/2015 06/10/2008 22/09/2009 01/09/2010 16/08/2011 12/09/2013 08/09/2015 28/10/2009 15/09/2015 18/10/2011 14/09/2009 15/09/2015 28/08/2009 02/09/2015 24/08/2009 02/09/2015 Atlantic salmon Low tolerance

Brook lamprey

Brook lamprey > ammocoete

Brown / sea trout

Bullhead

Grayling

Barbel Medium tolerance

Chub

Gudgeon

Minnow

Pike

Stone loach

3-spined stickleback High tolerance

69 UKTAG (2008) Rivers Assessment Methods Fish Fauna (Fisheries Classification Scheme 2 (FCS2)) ISBN: 978-1-906934-09-5 55 Appendix D Environmental Features Assessment

European eel

European eels > elvers

Perch

Roach

Tench

Blue orfe Non-native (Not assessed) Golden goldfish

Golden orfe

Golden tench

Koi carp

Mirror carp

56 Appendix D Environmental Features Assessment

D.3.3.4.2. Assessment  Species presence and distribution on the Itchen confirms that the fish community could be sensitive to reduced flows and deterioration in water quality.  No baseline WFD data are available downstream of Gaters Mill with which to characterise the ecological valuation of this community for the purpose of assessment. The boundary of the water body is, however, just 1km downstream of the Gaters Mill abstraction point.  Since the fish classification incorporates salmon Parr numbers in the assessment, these are unlikely to be affected by conditions downstream of Gaters Mill. Impacts downstream of Gaters Mill will only impact on migration of salmon into and up the river and have little impact on Parr survival. Impacts on Parr will be limited to recruitment through egg deposition and fry survival.  Impacts as a result of the Otterbourne drought order abstraction may have a greater bearing on the Parr survival as well as other fish species and therefore greater impact on the overall fish classification.  Hydrological assessments have shown that the frequency of implementation of the drought orders will be very low: - Neither the Allbrook & Highbridge nor the Riverside Park licence HOFs are breached during the historical climate conditions (1918 – 1997). - The stochastic flow time-series for Allbrook & Highbridge and Riverside Park shows that the Lower Itchen sources and Gaters Mill drought orders would only be required very infrequently.  Two important habitat variables through which the fish community may be linked to flow is through sensitivity to water velocity and depths. During the severe drought conditions when flows will fall below the licence HOFs under drought order powers: - Velocities at all cross-sections change very little from the licence HOFs and the proposed drought order HOFs (never more than 0.04m/s). At the three cross-sections where velocities are lowest (below 0.3 m/s), the change in velocity between the licence HOFs and the proposed drought order HOFs is very small (0.01 to 0.02 m/s). - Water depths at all cross-sections are maintained above 0.4m and unlikely to be limiting to fish passage and health. The risk of a deterioration in the High status of the fish classification in the Itchen WFD water body (GB107042022580) as a result of the drought orders in the Lower Itchen is low in the short term for interim classification and the longer term reporting cycle of the WFD.

D.3.2.4 Hydromorphological elements supporting the biological elements A number of hydromorphological elements are required to support the WFD biological assessment. These include:

 Hydrological regime: - Quantity and dynamics of water flow - Connection to groundwater bodies  River continuity  Morphological conditions: - River depth and width variation - Structure and substrate of the river bed - Structure of the riparian zone

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The current assessment of the hydromorphological elements is that it supports WF Good status:

 The drought conditions leading to implementation of the drought orders will be very infrequent, short-term and rapidly reversible in terms of the hydromorphological elements. The risk of deterioration in the hydromorphological elements as a result of the drought orders on the interim classifications and over the 6 year reporting cycle of the Itchen WFD water body is low.

D.3.2.5 Chemical and physico-chemical elements supporting the biological elements A number of chemical and physico-chemical elements are required to support the biological assessment. These include:

 General: - Thermal conditions - Oxygenation conditions - Salinity - Acidification status - Nutrient conditions The current assessment of the chemical and physico-chemical elements is that it supports WFD High status:

 During drought conditions, salinity and acidification will not be materially affected by implementation of the drought orders.  There has been a concern over the impact of the drought orders on the dilution available for sewage treatment work effluent discharges and hence on the nutrient and oxygenation conditions.  The drought conditions leading to the drought orders will be infrequent, short-term and rapidly reversible in terms of the chemical and physico-chemical elements. The risk of deterioration in the chemical and physico-chemical elements as a result of the drought orders on the interim classifications is low within the Itchen waterbody and over the 6 year reporting cycle is negligible.

D.3.2.6 Specific pollutants The status of specific pollutants are assessed as supporting elements to the ecological status and are assessed on the following basis:

 Pollution by all priority substances identified as being discharged into the body of water  Pollution by other substances identified as being discharged in significant quantities into the body of water The WFD status of specific pollutants is currently high.

During drought conditions, specific pollutants will not be materially affected by the implementation of the drought orders. There is no risk of deterioration in the specific pollutant element as a result of the drought orders on the Itchen water body.

58 Appendix D Environmental Features Assessment

D 3.3 Southampton Water transitional water body (GB520704202800) D.3.3.1 Macroinvertebrates The WFD Southampton Water transitional water body (GB520704202800) starts part-way along Riverside Park around 1km downstream of the Gaters Mill abstraction intake. Southampton Water is designated as a Heavily Modified Water body and the macroinvertebrate potential status in the WFD RBMP classification for Southampton Water is ‘Good’.

D.3.3.1.1 Baseline Benthic macroinvertebrate communities can be used to indicate the ecological status of an estuary or coastal water body.

The Infaunal Quality Index (IQI) is used to assess the ecological health of the benthic invertebrate fauna incorporating metrics of abundance, diversity and the presence and/or absence of pollution tolerant and disturbance-sensitive taxa. The individual metrics have been weighted and combined within the IQI in order to best describe the changes in the benthic invertebrate community in response to anthropogenic pressures. Each individual metric is assessed in relation to a reference value, which is the expected value for that metric in the habitat type that is being assessed when there is minimal or no disturbance due to human activities.

Benthic invertebrates are small animals (for example, worms, sand hoppers and clams) that live in the mud and sand at the bottom of the estuary or sea. They can be used to indicate the ecological status of a water body. Metrics on species composition and disturbance sensitivity are calculated with the IQI classification tool. The actual (observed) scores for these metrics are compared with a predicted score (reflecting a habitat in pristine condition). The comparison of the observed to expected scores is known as an Ecological Quality Ratio (EQR). EQRs are used to produce a benthic invertebrate IQI classification (High, Good, Moderate, Poor, Bad) of water bodies for Water Framework Directive (WFD) purposes.

The four class boundaries are:

 High/Good = 0.75  Good/Moderate = 0.64  Moderate/Poor = 0.44  Poor/Bad = 0.24. Each sample occasion takes 25 grab samples across the water body which are later analysed and indices calculated and averaged for the whole water body to give an overall status. Individual samples results ranged from poor to high giving an overall classification of Good. D.3.3.1.2 Assessment Table 23 summarises the available EQR data for Southampton Water. There are no monitoring locations for Southampton Water above Itchen Bridge on which to base a specific assessment of deterioration due to the impact of the drought orders.

Table 23 Southampton Water Benthic Invertebrate EQR data Sample date Average Species Average Sample IQI EQR Status richness May 2011 42 0.65 Good June 2013 44 0.68 Good

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Benthic macroinvertebrate species throughout the water body are, however, largely unaffected by freshwater inflows from the rivers. Depth profile data collection within the upper reaches of Southampton Water carried out by Southampton University suggest that there is stratification of the water body and that freshwater entering the estuary remains in the top 20cm of the water column temporarily but that full mixing occurs relatively quickly. The benthic invertebrates are buffered from this by the water column and experience only full salinity water conditions at the seabed through the tidal cycle.

The drought orders will not affect the tidal regime or elicit significant impacts on salinity gradients that could trigger a significant impact pathway. Consequently, there are limited mechanisms by which the benthic macroinvertebrates would be impacted by the drought orders under prevailing drought conditions and there is no risk of WFD status deterioration for this quality element.

D 3.3.2 Macroalgae Southampton Water is designated as a Heavily Modified Water body and the macroalgae potential status in the WFD RBMP classification for Southampton Water is ‘Good’.

D.3.3.2.1 Baseline Macroalgae communities (seaweeds) can be used to indicate the ecological status of an estuary or coastal water body. A number of tools are used to measure metrics of composition and abundance for different types of macroalgae communities. Up to two tools are used for assessing transitional water bodies: Opportunistic Macroalgae and Fucoid Extent. The tools compare actual (observed) metric scores against reference conditions (reflecting a water body in pristine condition). The comparison of the observed to expected scores is known as an Ecological Quality Ratio (EQR). The EQRs score from the tool assessments are used to produce the WFD macroalgae classification (High, Good, Moderate, Poor, Bad) for water bodies for Water Framework Directive (WFD) purposes.

Table 24 presents the macroalgae EQR data for Southampton Water.

Table 24 Southampton Water Macroalgae EQR data Sample date EQR Status 2008 0.69 Good 2010 0.62 Good 2013 0.60 Good

D.3.3.2.2 Assessment The drought orders will not affect the tidal regime or elicit significant impacts on salinity gradients that could trigger a significant impact pathway. Consequently, there are limited mechanisms by which the macroalgae would be impacted by the drought orders in prevailing drought conditions and there is no risk of WFD status deterioration for this quality element.

D.3.3.3 Fish D.3.3.3.1 Baseline To assess the ecological status of a transitional water body under the WFD, a statistically robust assessment of the observed health is compared against reference conditions for a minimally disturbed habitat – this is reported as an Ecological Quality Ratio (EQR). An EQR with a value of one represents reference conditions and a value of zero represents a severe impact.

WFD fish population survey results are classified using the WFD Transitional Fish Classification Index (TFCI) specifically designed for transitional waters.

60 Appendix D Environmental Features Assessment

The TFCI is a multi-metric index composed of ten individual components known as metrics, as set out below:

 Species composition  Presence of indicator species  Species relative abundance  Number of taxa that make up 90% of the abundance  Number of estuarine resident taxa  Number of estuarine-dependent marine taxa  Functional guild composition  Number of benthic invertebrate feeding taxa  Number of piscivorous taxa  Feeding guild composition The TFCI is calculated as the sum of all metric scores and converted into an EQR with a range from zero (a severe impact) to one (reference/minimally disturbed). The four class boundaries are:

 High/Good = 0.8  Good/Moderate = 0.6  Moderate/Poor = 0.4  Poor/Bad = 0.2 Fish are caught using a variety of techniques throughout each water body and the data are pooled over the most recent six year period. The pooled datasets can be used to indicate the ecological status of a transitional water body. There are ten metrics on various facets of composition and abundance designed to explore different components of species diversity in order to determine the health and quality of a transitional water body. The actual (observed) scores for these metrics are compared with a reference score derived from data collected in a similar way between 2006 and 2011. The comparison of the observed to expected scores is known as an Ecological Quality Ratio (EQR). EQRs are used to produce a classification (High, Good, Moderate, Poor, Bad) of each water body for Water Framework Directive (WFD) purposes.

Table 25 Southampton Water WFD Transitional Water Body Fish EQR Data Sample date EQR Status 2009 0.675 Good 2011 0.8 High 2012 0.8 High 2013 0.387 Poor 2014 0.536 Moderate 2015 0.639 Good 2016 0.674 Good

D 3.3.3.2 Assessment Freshwater flows to the Itchen estuary may have an impact on those fish looking to migrate up the river, such as migratory salmonids. However, the estuarine hydrology is dominated by the tidal cycle and the drought orders will not affect the tidal regime or elicit significant impacts on salinity gradients in drought conditions.

61 Appendix D Environmental Features Assessment

The impact on the migratory fish is considered to be sufficiently infrequent that the effects of other factors – such as the effects on estuarine water quality from disruptive activities in Southampton Water - will mask any effects of the drought orders on the migratory fish in the estuary. Other fish species are unlikely to be affected and hence the risk of WFD status deterioration within the Southampton Water WFD water body is likely to be negligible.

62 Appendix D Environmental Features Assessment

D4. NERC and notable species and habitats River Itchen SAC qualifying features, River Itchen SSSI notified features and WFD and ecological communities within the hydrological zone of influence have already been assessed in Section D2 and Section D3. The assessment presented encompasses effects on all ecological receptors including those habitats and species identified as being of principal importance for nature conservation under the Natural Environment and Rural Communities (NERC) Act (2006).

This section simply identifies those habitats and species already assessed that are also of principal importance for nature conservation under the NERC Act (2006). D.4.1. NERC species The following species have been identified from available data (Environment Agency monitoring data, SAC and SSSI citations) as being of principal importance for nature conservation under the NERC Act (2006):

Macroinvertebrates:

 Iron blue mayfly Nigrobaetis niger  Southern damselfly Coenagrion mercuriale Fish:

 Atlantic salmon Salmo salar  Brown/sea trout Salmo trutta  European eel Anguilla anguilla

D.4.2 NERC habitats The following habitats have been identified from available data (Environment Agency monitoring data, SAC and SSSI citations) as being of principal importance for nature conservation under the NERC Act (2006):

 Freshwater: Rivers (specifically, chalk rivers as defined under previous UK Biodiversity Action Plan (UKBAP) priority habitat definitions);  Grassland: Lowland meadows;  Wetland: Floodplain grazing marsh;  Wetland: Lowland fen.

D5. Non-native invasive species No non-native invasive species have been screened in for assessment. The drought orders are not considered to favour the propagation or dispersal of any known non-native invasive species within the hydrological zone of influence.

63 Appendix D Environmental Features Assessment