Author(s): C. M. Davis; J. F. Fox
Linked Author(s): James Fox
Keywords: Watershed; Isotopes; Sediment transport; Streambank erosion; Streambed storage
Abstract: Temporary sediment storage within the stream corridor can greatly influence sediment transport processes at the watershed scale. This study models natural stable isotopic and elemental nitrogen signatures of sediments in order to differentiate between fluvial erosion of cohesive streambank sediments and resuspension of temporarily stored streambed sediment within the transported sediment loading from a lowland watershed. In the present research contribution, a new model is formulated and applied to the Upper South Elkhorn Watershed, a lowland watershed in the Bluegrass Region of central Kentucky, which was selected for this study due to the pronounced streambank erosion and fine sediment storage processes within the system. The model formulation makes use of nitrogen isotopic and elemental differences between streambank sediments as compared to streambed sediments in a river system, of which the latter are unique due to biogeochemical changes including accumulation of organic matter and growth of microorganisms and benthic algae that can occur within the streambed stored sediment matrix. The model formulation incorporates the physical mixing of sediments from different sources in the stream reach of a watershed as well as the temporal change of sediments within in-stream storage zones due to nitrogen mineralization and isotopic fractionation during environmental processes. The model application in the Upper South Elkhorn Watershed relies on collection of samples of the streambank and streambed sediment sources as well as transported sediment samples collected at the watershed outlet that were thereafter analyzed using stable nitrogen isotopic ratio mass spectrometry and elemental analyses. The transported sediments illustrate the temporal variability of sediment transport processes throughout the watershed and together with water temperature allow calibration of the formulated model. The final model calibration estimates the fraction of transported sediment from the streambank and the streambed stored sediment sources and provides additional information regarding nitrogen isotopic fractionation, mineralization, and baseline nitrogen elemental and isotopic levels in the watershed system.
Year: 2009