Sources of stream bed sediment in an urbanized watershed

Excessive delivery of fine-grained sediment and sediment-bound nutrients to surface waters results in water quality impairment. Information on the relative contribution of different sources contributing sediment to river systems is a prerequisite to target management practices. The overall goal of this study was to determine the sources of stream bed sediment at a subwatershed scale using sediment fingerprinting approach in an urbanized, 31 km(2) Moore's Mill Creek watershed in Southern Piedmont region in Alabama, USA. The relative source contribution from construction sites and stream banks was quantified for two different particle size fractions, 63-212 mu m (fine sand) and < 63 mu m (silt and clay). Results of this study showed that both construction sites and stream banks were important sources of stream bed sediment. The stream bed sediment in the upstream reaches originated largely from channel bank sources, and in the lower reach (watershed outlet), construction sites were the dominant sources of stream bed sediment. The results of this study showed that the relative source contribution from different sources is dependent on the particle size of the sediment, time and location of sampling within a watershed, riparian buffers, and areas of construction activities in proximity to the sampling sites. Conservation practices in this watershed should be targeted to stream banks or construction sites depending upon the dominant source of stream bed sediment within a subwatershed. Overall, this study underscores the importance of considering the spatial and temporal variability of sediment sources as a function of sediment particle size for targeted implementation of best management practices.