Fingerprinting suspended sediment sources in the catchment of the River Ouse, Yorkshire, UK

Statistically veri®ed composite ®ngerprints and a multivariate mixing model have been employed to establish the main sources of the suspended sediment transported through the lower, non-tidal reaches of the River Ouse and one of its main tributaries, the River Wharfe, during the period 1994±1997. In the case of the suspended sediment samples collected from the River Ouse, the load-weighted mean contributions from uncultivated topsoil, cultivated topsoil and channel bank sources were estimated to be c. 25, 38 and 37%, respectively, while for the River Wharfe these sources contributed c. 70, 4 and 23%, respectively (c. 4% was derived from woodland topsoil). Suspended sediment samples collected during higher ̄ows evidenced a greater contribution from channel banks than samples collected during lower ̄ows. Source materials were also di€erentiated according to the three main geological source areas (Carboniferous, Permian and Triassic, and Jurassic) and their load-weighted mean contributions were estimated to be c. 24, 41 and 35% for the River Ouse and c. 91, 9 and 0% (there are no Jurassic rocks in this catchment) for the River Wharfe, respectively. When suspended sediment samples from tributary streams were used to characterize each geological source area, the equivalent results for the River Ouse were c. 30, 46 and 24%. Considering the three main tributaries that contribute to the River Ouse, the load-weighted mean contributions from the rivers Swale, Ure and Nidd were estimated to be 82, 15 and 3%, respectively. These values have been compared with estimates of the relative magnitude of the annual suspended sediment loads of these three rivers for the years 1995 and 1996 derived from continuous monitoring of discharge and turbidity. Di€erences between the two sets of results are ascribed to the di€erent periods of record involved and to the timing of suspended sediment sampling relative to the overall storm hydrograph, and thus the degree to which the available samples are representative of the overall suspended sediment ̄ux. Although a number of limitations must be recognized, the ®ngerprinting approach to source ascription is seen as providing valuable information regarding suspended sediment sources in the study catchments. Copyright # 1999 John Wiley & Sons, Ltd.