Fingerprinting suspended sediment sources in an urbanized watershed

Abstract

The elevated supply of fine-grained sediment to a river system negatively impacts the water quality and ecosystem health. Therefore, quantification of the relative contribution from different sources to in-stream sediment is of major interest to target sediment mitigation best management practices (BMPs). The objective of this study was to determine the relative contribution from different sources of suspended sediment in an urbanized watershed (31 km2) located in the eastern part of Alabama, USA. Estimates of relative contributions from individual source types were assessed for two different particle size fractions, 63-212μm (fine sand) and < 63μm (silt and clay). Results of this study indicate that the construction sites were the dominant source of suspended sediment in this watershed. The average annual subwatershed-level surface runoff determined using the Soil and Water Assessment Tool (SWAT) model varied from 2.3 to 11,980 mm ha-1 year-1. Areas that generate high surface runoff have the potential to contribute disproportionately high amounts of sediment to streams and therefore should be targeted for BMPs. The results of this study show that it is important to consider spatial and temporal variability in suspended sediment sources in order to develop and target sediment control management strategies. The sources of suspended sediment and sediment deposited on the stream bed might not necessarily be the same. Therefore, sampling both suspended sediment and stream bed sediment will improve our knowledge of watershed-level sediment transport processes.