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Preparing for climate change impacts on freshwater ecosystems (PRINCE): literature review and proposal methodology Science Report: SC030300/PR Authors: Science at the Environment Agency Executive Summary

Kieran Conlan, Stuart Lane, Steve Ormerod, Trevor Wade, Steve Killeen
Project record Preparing for climate change impacts on freshwater ecosystems (PRINCE): Literature review and proposal methodology The Environment Agency is the leading public body protecting and improving the environment in England and Wales. It's our job to make sure that air, land and water are looked after by everyone in today's society, so that tomorrow's generations inherit a cleaner, healthier world. Our work includes tackling flooding and pollution incidents, reducing industry's impacts
more » ... industry's impacts on the environment, cleaning up rivers, coastal waters and contaminated land, and improving wildlife habitats. A freshwater ecosystem typology was developed for the PRINCE project to group freshwater environments that may have similar climate sensitivities. The typology drew on international and national regulations and typologies where relevant. Three classes were identified: • rivers and streams: upland and lowland headwaters, middle and lower river reaches, and predominantly groundwater-fed rivers (chalk or sandstone); • standing open waters and canals: lakes (eutrophic to dystrophic), ditches, ponds, canals and reservoirs; • wetlands and washlands: grazing marsh and improved grasslands on floodplain, lowland raised bog, fens, reedbeds and wet woodlands. Key non-biological factors that influence ecosystem dynamics Project record Preparing for climate change impacts on freshwater ecosystems (PRINCE): Literature review and proposal methodology connectivity. In addition, the frequency, timing and magnitude of extreme events of both low and high discharge will change markedly in future climates. The consequences for habitat configuration, availability and quality will depend both on local conditions and on the habitat distribution or adaptability of affected organisms. Water-quality effects Most potentially significant water-quality effects will be associated with hotter summers and lower rainfall. During these the reduction in dissolved oxygen carrying capacity and higher biochemical oxygen demand (because the effluents will be diluted less and there will be more algal and/or microbial growth) are likely to combine to produce increased risk of deoxygenation. This may be particularly important in middle and lower river reaches and standing waters, in which re-aeration may be reduced. Increased macrophyte growth encouraged by higher water temperatures and non-limiting nutrient supply could further reduce oxygen levels and pose threats to fish and invertebrates. It is likely that changes in sediment mobility driven by climate change will affect the transport and deposition of a wide range of solutes and pollutants. Higher flows and lower water temperatures should combine to limit water-quality impacts in winter, although increased storminess may increase run-off of contaminants into watercourses. Solar radiation effects Solar radiation impacts directly on the timing of specific events (phenology). Changes in solar radiation dictate the time sequences in, for example, algal growth and rates of production. These responses can have implications for higher parts of the food web, such as zooplankton and fish. There is potential for food supplies to become out of sequence when, for example, young fish hatch before their food supply is available. Ecological sensitivity to climate change All of the freshwater ecosystems considered are sensitive to climatic change, either directly (e.g., through temperature and rainfall-mediated effects) or indirectly through hydrological, water quality or competing ecological impacts. Sensitivity of freshwater ecosystems to climate change will depend on two major components. Firstly, on the magnitude, frequency (return period), timing (seasonality), variability (averages and extremes) and direction of predicted climate changes. Secondly, on the sensitivity and resilience of the ecosystem, habitat and/or species to that change. In general, ecosystems at the extreme range of their supported environmental conditions will be most affected. For example, these include changes in distribution for organisms sensitive to: • increased temperature in low-temperature habitats of restricted distribution (e.g., cold-water stenotherms at high altitude); • major increase in drought frequency (e.g., salmonids that require spawning and juvenile habitat in upland tributaries, species within lowland raised bog in the southeast); • increased flood and erosion risk in flood-sensitive habitats (e.g., floodplain grazing marsh and reedbed). Project record Preparing for climate change impacts on freshwater ecosystems (PRINCE): Literature review and proposal methodology Locations at which to trial the approaches have been determined largely by data availability for model calibration and verification. Initial studies will test the influence of climate change on ecosystem drivers, including hydrology, hydrochemistry, sediments and thermal regime. The upper Wharfe catchment (Yorkshire) will be modelled using the deterministic CAS-Hydro framework. The Flood Estimation Handbook (FEH) approach to flow derivation will also be applied to compare results from CAS-Hydro with simpler statistical methods. Climate scenarios will be produced for the 2020s and 2050s using a range of GCMs to capture uncertainties that result from the choice of climate model and the downscaling approach. CAS-Hydro outputs will be used as inputs for empirical models of in-channel macroinvertebrate dynamics and to estimate useable habitat availability for Project record Preparing for climate change impacts on freshwater ecosystems (PRINCE): Literature review and proposal methodology macroinvertebrates and fish. The resultant climate-driven changes to the aquatic environment will be analysed to assess implications for the relevant assemblages. A second study will use FEH-derived data as inputs to an empirical model of macroinvertebrates for the upper Tywi (mid Wales), using the long-term Cardiff University dataset.