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Streambank legacy sediment contributions to suspended sediment‐bound nutrient yields from a Mid‐Atlantic, Piedmont watershed

350 210 Stroud Water Research Center

Jiang, G., A. Lutgen, K. Mattern, N. Sienkiewicz, J. Kan, and S. Inamdar. 2020. Journal of the American Water Resources Association, early online access.

https://doi.org/10.1111/1752-1688.12855

Abstract

While streambank legacy sediment has been increasingly recognized as an important contributor of fine sediment to watersheds, little is known about its contributions to suspended sediment‐bound nutrients. This uncertainty is exacerbated by the ubiquitous presence of legacy sediments in valley‐bottoms of the Mid‐Atlantic region of the United States. Using a sediment fingerprinting model, we quantified suspended sediment and sediment‐bound nutrient sources for a 114 km2 agricultural, Piedmont watershed. Sediment sources included agricultural, developed, and forested soils as well as streambanks legacy sediments. Suspended sediment and sediment‐bound nitrogen (N) and phosphorus (P) concentrations were determined for 10 storms over the study period of August 1, 2017 to July 31, 2018. Streambanks contributed 50% of the annual suspended sediment yield of 1,348 kg/ha followed by agricultural (49%) and forested (1%) soils. Streambanks amounted to 26% and 32% of the suspended sediment‐bound N and P exports, respectively, whereas the corresponding loads from agricultural sources were 73 and 67%, respectively. Bank contributions varied with storm magnitude and seasonality, with the highest exports associated with the largest peak flows. These results highlight that streambank sediments constitute a significant fraction of suspended sediment‐bound nutrient exports and must be considered in watershed models, regulatory assessments, and management practices.