Changing suspended sediment and particulate phosphorus loads and pathways in underdrained lowland agricultural catchments; Herefordshire and Worcestershire, UK

Data obtained from a small ( 150 ha) experimental catchment, Hereford U. K., have shown that land drains contributed > 50% of the total catchment suspended sediment ( SS) yield over a two year period. In one of the monitored drains, annual sediment yields were 964 and 978 kg ha(-1). Particulate phosphorus (PP) contributed > 60% of total phosphorus lost through the drains and at least 73% of the total drain load came from topsoil. A major question that was not answered by the monitoring programme was whether SS and PP loads had increased since the drains had been installed between the 1960s and 1980s. To address this problem, a sediment yield record was reconstructed from the Kyre Pool catchment in Worcestershire that has a similar drainage history and soil types. Reservoir sediments were dated using the Pb-210 crs method and results suggest a fourfold increase in SS yield ( 300 - 1170 kg ha(-1) yr(-1)) and PP loads (0.19 - 0.79 kg ha(-1) yr(-1)) since the 1960s. The most recent SS and PP loads are comparable to those obtained from catchment monitoring. The high lake sediment Cs-137 inventory suggests a significant influx of eroded topsoil and Cs-137 activities in the most recent lake sediments are comparable to those of monitored land drains, supporting the hypothesis that land drainage has had a major impact on SS and PP yields and pathways.