Suspended sediment sources in two small lowland agricultural catchments in the UK

In recent years there has been increasing recognition of the need to include sediment control strategies within catchment management plans. Information on the source of the sediment transported by a river is an important requirement for designing effective sediment control strategies. This paper uses the source fingerprinting approach to establish suspended sediment sources within two small (<4 km2) lowland agricultural catchments in the UK, which are both extensively under drained. Representative samples of suspended sediment were collected from both catchments to encompass the expected inter- and intra-storm variability in sediment source. Statistically verified composite fingerprints and multivariate mixing models, incorporating particle size correction factors, were used to estimate the relative contribution of the potential sediment sources. These included surface sources (classified by land use, geology and soil type), eroding channel banks and field drains (subsurface sources). Field drains were shown to be important suspended sediment sources in both catchments, accounting for 27–55% of the sediment yields. Bank erosion contributes ca. 10% or less of the sediment yields. Surface sources were found to be important in both catchments contributing between 34–65% of the sediment yield. The above estimates of the relative contribution of the individual sediment sources within the study catchments to the overall sediment yield were shown to conceal significant inter- and intra-storm variability in the source contributions.