The effectiveness of field wetlands in retaining pollutants from agricultural runoff: case studies from the UK.

Abstract

Field wetlands are one option available to farmers for mitigation of diffuse pollution from agriculture. Although used worldwide, there is little evidence for their effectiveness in the UK agricultural landscape. This paper describes the construction and monitoring of ten wetlands in the UK, with different combinations of soil type, wetland design, wetland size and runoff source. In the first two years after construction, all the wetlands trapped a substantial amount of sediment, with sandy sites having the highest trapping rates (>0.5 t ha^-1 yr^-1), followed by silty sites (0.02-0.4 t ha^-1 yr^-1) and clay sites (0.01-0.07 t ha^-1 yr^-1), although the lower rainfall at the clay sites was a confounding factor. Phosphorus trapping rates in the first year varied from 0.006-1 kg ha^-1 yr^-1. Overall, small field wetlands were shown to be an effective land management option for trapping sediment and nutrients.