Location: Southwest Watershed ResearchTitle: Fingerprinting the sources of suspended sediment delivery to a large municipal drinking water reservoir: Falls Lake, Neuse River, North Carolina, USA Author
Submitted to: Journal of Soils and Sediments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2013
Publication Date: 9/24/2013
Citation: Voli, M., Wehmann, K., Bohnenstiehl, D., Leithold, E., Osburn, C., Polyakov, V.O. 2013. Fingerprinting the sources of suspended sediment delivery to a large municipal drinking water reservoir: Falls Lake, Neuse River, North Carolina, USA. Journal of Soils and Sediments. 3:1692–1707. DOI: 10.1007/s11368-013-0758-3. Interpretive Summary: Geochemical fingerprinting analysis was used to identify the sources of sediment contamination in a North Carolina reservoir. Stream bank erosion was found to be the largest contributor.
Technical Abstract: We employ a novel geochemical-fingerprinting approach to estimate the source of suspended sediments collected from tributaries entering Falls Lake, a 50 km2 drinking water reservoir on the Neuse River, North Carolina. Many of the major tributaries to the lake are on North Carolina’s 303(d) list for impaired streams, and in 2008 the lake was added to that list because of high values of turbidity, likely the result of high suspended sediment loads delivered to the reservoir by tributary streams. Suspended sediments were collected from four streams with a time-integrated sampler during high-flow events. In addition, composite sediment samples representing potential sources were collected from stream banks, forests, pastures, construction sites, dirt and paved roads, and road cuts within each tributary catchment. Radiocarbon dating and magnetic susceptibility measurements were used to determine the origin of often thick and highly erosive alluvial deposits exposed in stream banks. Sediment samples were analyzed for the concentrations of 55 elements and two radionuclides in order to identify tracers capable of distinguishing between potential sediment sources. The relative sediment source contributions were determined by applying a Monte Carlo simulation that parameterized the geochemical tracer data in a mixing model. Radiocarbon and magnetic susceptibility measurements confirmed the presence of “legacy” sediment in the Ellerbe and New Light Creek valley bottoms. Mixing model results demonstrate that stream bank erosion is the largest contributor to the suspended sediment load in New Light Creek (62%), Ellerbe Creek (58%), and Lick Creek (33%), and is the second largest contributor in Lick Creek (27%) behind construction sites (43%). This study reveals that stream bank erosion is the largest contributor to the nonpoint-source suspended sediment load in three of the four catchments, and is therefore a significant source of turbidity in Falls Lake. The presence of legacy sediment appears to coincide with increased contributions from stream bank erosion in Ellerbe and New Light creeks. Active construction sites and timber harvesting were also significant sources of sediment. Water quality mitigation efforts need to consider nonpoint-source contributions from stream bank erosion of valley-bottom sediments aggraded after European settlement.