Source type ascription for fluvial suspended sediment based on a quantitative composite fingerprinting technique

We report the successful application of a quantitative composite fingerprinting technique, incorporating both a rigorous statistical verification procedure for composite signatures and a multivariate mixing model, to evaluate sediment source type in the Dart catchment, Devon, UK and the Plynlimon experimental catchment, Powys, UK. Quantitative ascription of source types is discussed in terms of the mean contributions and potential seasonal, inter- and intea-storm variations in the relative contributions of surface erosion from a number of distinct land use categories and of channel erosion to the suspended sediment load sampled at various sites within the study areas. Surface erosion of pasture soils is generally important in both study catchments but the impacts of spring and autumn cultivation in the Dart, and of autumn and winter forestry activity at Plynlimon, are also evident. Inter-storm variations in sediment source type reflect antecedent conditions, variable contributing areas and timing of sediment sample collection, and highlight the individuality of catchment response for the sampled flood events. Intra-storm variations in source type contributions emphasize the necessity for detailed sampling programmes for suspended sediment in storm periods, when using the fingerprinting approach to investigate sediment origin.