Effects of agricultural land management changes on surface water quality: A review of meso-scale catchment research

Measuring the environmental impacts of agricultural practice is critical for policy formulation and review, including policies implemented to improve water quality. Here, studies that measured such impacts in surface waters of hydrologically diverse meso-scale catchments (1-100 km2) were reviewed. Positive water quality effects were measured in 17 out of 25 reviewed studies. Successful farm practices included improved landscape engineering, improved crop management and reductions in farming intensity. Positive effects occurred from 1 to 10 years after the measures were implemented, with the response time broadly increasing with catchment size. However, it took from 4 to 20 years to confidently detect the effects. Policy makers and scientists should account for these hydrological and biogeochemical time lags when setting policy and planning monitoring in meso-scale catchments. To successfully measure policy effects, rates of practice change should also be measured with targeted water quality parameters.