Grassed buffer strips for the control of nitrate leaching to surface waters in headwater catchments

The use of riparian buffer strips is a possible strategy for controlling di ffuse nitrate pollution of surface water in agricultural catchments. Data c ollected from paired buffered and unbuffered headwater catchments at three sites with conditions representative of much of the agricultural land in En gland and Wales, showed that grassed buffers did not substantially reduce n itrate-nitrogen concentrations entering the streams. Median nitrate-nitroge n levels observed in buffered catchments ranged from 7.6 to 18.8 mgN l(-1), but peaked at up to 46.1 mgN l(-1). The existence of preferential bypass h ow paths during the winter flow events limited the effectiveness of nitrate removing processes within the strips. The findings suggest that grassed ri parian buffer strips may not be effective in controlling diffuse nitrate po llution unless the hydrology of the strip allows a suitable environment for denitrification and/or plant uptake. Grassed buffer strips should be caref ully targeted or, alternatively, engineered to ensure adequate residence ti me of solutes within the strip. (C) 1999 Published by Elsevier Science B.V. All rights reserved.