Assessing Impacts of Combined Sewage Overflows and Surface Water Outfalls on Invertebrate Populations in River Catchments in Southwest England (5059)

Freshwater systems are considered to be the most threatened globally and chemical pollution has contributed significantly to freshwater wildlife population declines. It is important to understand the different pollution sources and their impact on freshwater biodiversity so that mitigation strategies can be prioritised for the best wildlife protection.

Combined Sewer Overflows (CSO) have hit the media headlines in recent years and there is widespread concern about their environmental impacts on freshwater biota however these concerns are largely unquantified. We recently secured a major grant to better understand the impacts of Combined Sewer Overflows (CSO) and Surface Water Outfalls (SWO) on riverine biota across catchments in southwest England (rivers Exe, Tamar and Dart) that will support this PhD research project.

The PhD will therefore be part of an exciting large multidisciplinary research project with diverse supporting expertise and industry engagement for enabling real world impact. The PhD will involve a combination of in-field sampling, invertebrate monitoring using both traditional and eDNA methods, chemical bioavailability assessments (for selected chemicals identified in the CSO and SWO discharges through the wider research programme), and risk analyses/modelling using these data together with wider invertebrate/chemical monitoring and ecotox database information.

Importantly, the project has great flexibility and the student will get every opportunity to help shape the PhD project to suit their main interests and training preferences. Project Aims and Methods:

The overall aim of this project is to quantify the impacts of CSO/SWO on invertebrates populations to support freshwater biodiversity protection in rivers in southwest England. The research project will involve river sampling of benthic macroinvertebrates and water/sediment samples (for eDNA) at points of (chemically-profiled) CSO/SWO discharges into the study rivers, the edge of the mixing zone (established for each specific study site ) and at sites in receiving waters at distances above and below these discharges for multiple seasonal timepoints. eDNA profiling for invertebrate presence at these sites will be conducted on water and sediment samples via DNA sequencing which we run routinely in our laboratories at Exeter.

Invertebrate body burdens of selected chemicals identified in the CSO/SWO discharges of potential toxicological concern (e.g. selected metals, pesticides etc.) will be measured via ICP-MS/LC-MS. Modelling work using these data (and wider data sets) will assess the relative risks of CSO and SWO in receiving rivers to invertebrate populations across southwest England considering wider natural variations in the ecology and characteristics of these rivers (which are broadly representative of the range of upland to lowland rivers in the UK).

Collectively, this work will inform on the impacts of CSO and SWO discharges on riverine ecology in southwest England and support Southwest Water in their planning and decision making for investments as well as impacting decision-making more widely across the UK water industry via knowledge exchange from the Centre for Resilience in Environment, Water and Waste.

Project partners: Southwest Water (Paul McNie, [email protected])

Southwest Water are providing almost half the project costs for this PhD and will dedicate staff time commitments to support the student training , data provision, and equipment access.