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«TECHNICAL APPENDIX D ECOLOGICAL DATA AND LITERATURE REVIEW Cascade Consulting Technical Appendix D Thames Water Utilities Ltd 2W0H Lower Thames ...»

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Thames Water Utilities Ltd

2W0H Lower Thames Operating Agreement Final





Cascade Consulting Technical Appendix D

Thames Water Utilities Ltd

2W0H Lower Thames Operating Agreement Final Confidential Table of Contents Summary

D.1  Overview – Literature and Data Collation and Review

D.1.1  Introduction

D.1.2  Methodology for Stage 1 Review

D.2  Fish Communities of the Lower Freshwater River Thames

D.2.1  Literature Review of Impacts on Freshwater Fisheries

D.2.2  Data Review and Gap Analysis

D.2.3  Specification of Impact Assessment

D.3  Fish Communities of the Thames Tideway

D.3.1  Literature Review of Impacts on Transitional Water Fisheries

D.3.2  Data Review and Gap Analysis

D.3.3  Specification of Impact Assessment

D.4  Macroinvertebrate Communities of the Lower Freshwater River Thames.71  D.4.1  Literature Review of Impacts on Freshwater Macroinvertebrate Communities........ 71  D.4.2  Data Review and Gap Analysis

D.4.3  Specification of Impact Assessment

D.5  Macroinvertebrate Communities of the Thames Tideway

D.5.1  Literature Review of Impacts on Estuarine Invertebrates

D.5.2  Data Review and Gap Analysis

D.5.3  Specification of Impact Assessment

D.6  Species of Conservation Interest

D.6.1  Literature Review of Impacts on Molluscan Species of Conservation Interest........ 121  D.6.2  Data Review and Gap Analysis

D.6.3  Specification of Impact Assessment

D.7  Invasive Species

D.7.1  Literature Review of Impacts on Invasive Species

D.7.2  Data Review and Gap Analysis

D.7.3  Specification of Impact Assessment

D.8  Conclusions

D.8.1  Freshwater Fish

D.8.2  Estuarine Fish

D.8.3  Freshwater Macroinvertebrates

D.8.4  Estuarine Macroinvertebrates

D.8.5  Species of Conservation Interest/Invasive Species

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SUMMARY This appendix establishes the ecological data and assessment methodologies to be undertaken during the Stage 1 LTOA ecological preliminary impact assessment. A literature review is presented that considers the direct and indirect impacts of changes in hydrological regime on key groups of aquatic ecological receptors. For each of the key receptor groups a review is undertaken of the monitoring data currently available together with a gap analysis to establish its utility for subsequent ecological assessments (Appendix F).

The working boundary of the study area has been agreed between Thames Water and the Environment Agency. The upstream limit is at the Windsor flow gauge on the River Thames, upstream of Thames Water’s Datchet intake (the most upstream of the intakes included in the LTOA). The downstream limit is London Bridge in the Thames Tideway. Key groups of ecological receptors that have been included in the review are; freshwater fish in the Lower Thames, estuarine and migratory fish in the Upper Thames Tideway, freshwater macroinvertebrate communities of the Lower Freshwater Thames, macroinvertebrate communities of the Upper Thames Tideway, macroinvertebrate species of conservation concern and invasive species.

The data availability review has informed the scope of work that can be usefully undertaken in the Stage 1 preliminary ecological impact assessment (in Appendix F); and makes recommendations on identifying additional specific data requirements for Stage 2.

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D.1.1 Introduction The key objective of Stage 1 of the Lower Thames Operating Agreement (LTOA) study is to make an assessment of whether the existing abstraction and its control through the LTOA is having a significant adverse impact on the aquatic environment. The scoping report1 made

recommendations of work items for Stage 1 and these are reproduced verbatim below:

• Ecological literature/data review. Considerable uncertainty exists in the exact extent of monitoring required for ecological receptors. This early review will help target potential issues specifically related to changing flow or level and focus further investigations. Key elements include: analysis of the considerable existing data set;

and, identification and development of new tools to analyse ecological data e.g.

development of community conservation index for use in brackish environments.

• Non-native species/species of conservation interest. Both raised as specific issues with respect to potential impact of abstraction. A potential impact on either of these has the potential to impose an additional level of regulation on the review and may lead to considerable extra work. Early investigation will determine whether the issue can be dismissed or whether it will require extensive further investigation. An initial assessment of potential links, pathways, sensitivity and risks is required.

Ecological receptors identified in the Scoping Report are given in column 1 of Table 6.1.

Groups of receptors where data availability is known to be poor, for example, for those receptors that are not the subject of routine Environment Agency monitoring programmes and/or those receptors where supporting literature identifying key habitat preferences and constraints is sparse, have been scoped out of the Stage 1 review. Where relevant certain receptors have been scoped into Stage 2, with those considered uninformative scoped out as discussed in Section 6 of the main report.

Thames Water (2008) Scoping study for a work programme for assessment of the impact of the Lower Thames Operating 1 Agreement on the Lower River Thames. Report prepared by Atkins, March 2008.

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D.1.2 Methodology for Stage 1 Review Receptors have been considered as groups of organisms e.g. benthic macroinvertebrate communities, freshwater fish communities or individual species where this is appropriate e.g. for species of conservation concern such as depressed river mussel. An extensive literature review of impacts of abstraction and effects of key hydrological and physicochemical parameters has been carried out for each of the key groups or species and is presented in the relevant sections of the report below. The hydrological and water quality context for the ecological review is described in Technical Appendices B and C respectively.

Stage 1 has compiled and reviewed the existing ecological data for the receptors (including

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data for non-native species and species of conservation interest). Data have been reviewed in terms of data availability and the utility of available data for undertaking ecological impact assessment of the current operating regime. The review methodology is given in Figure D.1.

Identification of key activities and impact pathways for assessment has been carried out and both direct impacts (e.g. fish entrainment) and indirect impacts (e.g. impacts to ecology mediated through changes to water quality) identified. This desk-study appendix describes the available ecological data in terms of its suitability for undertaking an assessment of the significance of Thames Water’s abstractions managed by the LTOA. As such it provides an overview of the availability of monitoring data for each receptor within the study area and an assessment of the need to collect any further data. Recommendations for monitoring and analysis as part of Stage 2 of the LTOA review are given in Section 7 of the main report.

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D.2.1 Literature Review of Impacts on Freshwater Fisheries D.2.1.1 Evidence from abstractions in other major temperate lowland rivers/estuaries Information on the impact of abstractions on fisheries in other lowland rivers is rather limited in the literature. Most of the information refers to the social consequences (e.g.

impacts of flooding) rather than the ecology. This is largely because the information is contained in grey literature associated with Review of Consents and Drought Orders. These studies include for example United Utilities abstraction and drought study assessments for the Rivers Eden, Ehen, Lune and Leven; Yorkshire Water’s time limited licence assessments on the River Ouse and Aire; and Wessex Water’s AMP4 investigations of the Hampshire Avon. A thorough meta-analysis of these documents would be required to extract the information, if such information was made available by the different water companies.

However, the findings are relatively dissimilar to those for the LTOA in both scale and receiving water ecosystem types. Notwithstanding, there are anecdotal concerns about the impacts of abstractions on fisheries for a number of rivers including the Tyne, Ancholme, Great Ouse, Yorkshire Ouse and Trent. These usually concern impingement on screens, depleted flows in affected reaches, fluctuations in water levels and loss of connectivity with the floodplain, and their affects of fish recruitment and community structure. Each of these issues will be considered during the Stage 1 and/or Stage 2 assessments.

D.2.1.2 Key hydrological and physico-chemical parameters

In large lowland rivers (LLRs) such as the Thames, the hydrological regime is a key driver of population and community dynamics. The flow regime affects fish both directly (forming a fish’s hydraulic habitat - its ability to cope with certain flow velocities) and indirectly (forming a fish’s physical habitat through geomorphological processes). Although these two factors do not act independently (hydrology influences channel structure and vice versa) the analysis of a fish’s requirements must consider both elements of its preferred habitat, “hydraulic” and “physical” to manage flows (regulation, abstraction and discharge) and maximise the success of rehabilitation/mitigation efforts. To some extent the flow regime also dictates the temperature regime and other aspects of water quality within the system, another master variable affecting the ecological status of rivers and fisheries in particular (Cowx 2001; Nunn et al, 2007a). Flow is a generic term that encompasses several elements that are widely recognised as being of ecological importance (including velocity, wetted width, depth etc) and essential in the maintenance of sustainable fisheries and the habitat on which they depend. The magnitude, frequency, duration, timing and predictability of flows are vital components of a fish’s habitat (Lytle and Poff, 2004) and therefore must be maintained to ensure that a water body exhibits good ecological status or good ecological potential in accordance with the Habitats and Water Framework Directives. The provision of

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adequate and appropriate flow parameters is a key requirement for the maintenance/restoration of good ecological status in the River Thames.

It is important to note that the conditions found in present day LLRs may not reflect the natural (optimum Poff et al, 1997) conditions that once existed before heavy human modification took place. It is known that the biota in modified rivers react very differently to that in natural systems due to factors such as floodplain isolation and channel modification (Nunn et al, 2007b), and this is typical of the lower Thames. This complicates the question of whether to maintain status quo or restore a “natural” flow regime because flows that would naturally result in floodplain inundation have a very different effect on biota when the river is constrained to its channel. For example, it may be that reducing flows as a result of abstraction, particularly around the spawning period, would have advantages in channelised rivers because fish displacement may be reduced.

Species habitat requirements Knowledge of the individual habitat preferences of each species within fish communities is required to reveal the underlying conditions that drive community characterisation. In terms

of flow-related issues these requirements include:

• the determination of basic habitat requirements for all life stages of fish species in rivers, and the seasonal habitat changes required to maintain population status;

• the determination of critical flow related factors affecting the various life stages of fish species in rivers;

• from the above, identification of key seasonal habitat requirements in relation to flow and water.

The first step to achieving this was to review the flow-related habitat requirements of the various life stages of the main freshwater species found in the UK. This information was used to identify which characteristics of flow regimes/hydrographs have biological significance in determining fish community structure in various river types.

Fish community structure and functioning is directly related to the variety and extent of natural habitats within a river basin (Cowx and Welcomme, 1998). Consequently, the functional complexity of stream ecosystems must be maintained to ensure unaltered, healthy and diverse fish populations and community structure. This functional complexity is mainly dependant on geomorphological and hydrological processes that dictate channel morphology and influence riparian vegetation and floodplain habitats. Riverine habitats are strongly influenced by interactions with the surrounding landscape, more so than other terrestrial ecosystems that typically have well defined boundaries. Riverine habitats are therefore shaped by processes within the riparian corridor and the basin as a whole (Cowx and Welcomme, 1998).

Habitat, in its broadest sense, is defined as the usable area of stream in which a fish species

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