Mitigating Agricultural Diffuse Pollution: Learning from The River Eden Demonstration Test Catchment Experiments

Freshwater systems continue to fail to achieve their ecological potential and provide associated ecological services due to poor water quality. A key driver of the failure to achieve good status under the EU Water Framework Directive derives from non-point (diffuse) pollution of sediment, phosphorus and nitrogen from agricultural landscapes. While many mitigation options exist, a framework is lacking which provides a holistic understanding of the impact of mitigation scheme design on catchment function and agronomics. The River Eden Demonstration Test Catchment project (2009-2017) in NW England uses an interdisciplinary approach including catchment hydrology, sediment-nutrient fluxes and farmer attitudes, to understand ecological function and diffuse pollution mitigation feature performance. Water flow (both surface and groundwater) and quality monitoring focused on three ca. 10km2 catchments with N and P measurements every 30 minutes. Ecological status was determined by monthly diatom community analysis and supplemented by macrophyte, macroinvertebrate and fish surveys. Changes in erosion potential and hydrological connectivity were monitored using extensive Landsat images and detailed UAV monitoring. Simulation modelling work utilised hydrological simulation models (CRAFT, CRUM3 and HBV-Light) and SCIMAP based risk mapping. Farmer behaviour and attitudes have been assessed with surveys, interviews and diaries. A suite of mitigation features have been installed including changes to land management - e.g. aeriation, storage features within a `treatment train', riparian fencing and woodland creation. A detailed dataset of the integrated catchment hydrological, water quality and ecological behaviour over multiple years, including a drought period and an extreme rainfall event, highlights the interaction between ecology, hydrological and nutrient dynamics that are driven by sediment and nutrients exported within a small number of high magnitude storm events. Hence these high-resolution processes must be studied in conjunction, rather than in isolation, to understand system dynamics and critically to evaluate effective mitigation schemes.