Climate change eutrophication risk mapping for England - Phase 1. Project outputs report

Purpose of this report: This report has been produced for the purpose of describing the methods and results of modelling work undertaken for the Environment Agency, to indicate the possible effects of climate change and future potential improvements in wastewater treatment on concentrations of phosphorus at selected river monitoring sites in England. This work represents the first phase of a wider project to predict how climate change might increase the risk of eutrophication of surface waters. Methods: The methodology for predicting phosphorus concentrations in rivers is based around the use of the CEH Load Apportionment Model (LAM). This model apportions observed phosphorus loads between diffuse and point source inputs, as a function of flow. Models were developed for 115 WFD waterbodies based on recent measurements of phosphorus concentration and flow. These models were then used with Future Flows Hydrology datasets, which provide projections of future river flows including the effects of climate change, to indicate how phosphorus concentrations in watercourses might be impacted by climate change. Additional model scenario predictions predict the impact on in-stream phosphorus concentrations of potential improvements in sewage effluent quality. Results: The key outputs of the project are a series of spreadsheets and maps (provided as GIS layers). The spreadsheets provide a means of visualising and analysing the outputs of the Load Apportionment Model and predict future WFD status at each of 115 river monitoring sites across England. The maps provide a means of visualising the same results spatially. Climate change is predicted to cause generally small increases in annual average phosphorus concentrations in rivers but associated WFD status is unlikely to change significantly as a result of the flow changes alone. Improvements in wastewater treatment have the potential to cause reductions in phosphorus concentrations which are greater in magnitude than the increases due to climate change. Changes in summer month and low flow period phosphorus concentrations are of more direct relevance to eutrophication risks than annual averages and show greater rates of increase as low flows are projected to decline.