Do agri-environment schemes result in improved water quality?

Improved water quality, through a reduction in diffuse pollution from agricultural sources, is an expected benefit of agri-environment schemes, but this has yet to be demonstrated in practice. Here, we evaluate the impact of Welsh agri-environment schemes on water quality and freshwater ecosystem condition through a combined monitoring and modelling framework.
To determine the influence of the agri-environment schemes on ecosystem condition, spatially independent catchments dominated by a single scheme (>40% of catchment) were compared to control catchments dominated (>70%) by agricultural land that was not part of any scheme. Biological indicators of water quality were monitored at the outfall of each catchment and a spatially explicit modelling framework of diffuse pollutant emissions applied to each of the 80 catchments.
Direct comparison (scheme/non-scheme) was unable to identify any significant effect of agri-environment scheme participation. However, derived biological ind...