Stream bank legacy sediment and nutrient contributions to mid-Atlantic watershed nutrient exports
Abstract
Sediments and sediment-associated contaminants have been identified as the leading cause of water quality impairment in the Chesapeake Bay watershed. Suspended sediment yields are highest in the Piedmont, attributed to erosion of stream bank legacy sediments. Stream bank erosion may be responsible for 50-100% of Piedmont suspended sediment yields, but little is known about the contribution of stream bank legacy sediments to mid-Atlantic watershed nutrient (C, N, P) exports.
This study examines the role of stream bank legacy sediments in mid-Atlantic sediment and nutrient budgets by: (1) determining sources of fine-grained suspended sediment in a mid-Atlantic watershed through sediment fingerprinting; (2) integrating sediment fingerprinting results with high-resolution turbidity and discharge data to generate annual and event-scale sediment and nutrient budgets; and (3) evaluating differences in stream bank legacy sediment and nutrient contributions based on seasonal, antecedent, and precipitation conditions. Data from eight storms and seven months of stream bed sampling are presented from the Big Elk Creek, a 133.6 km2 agriculture-dominated Piedmont tributary of the Chesapeake Bay. Sediment source samples were collected from upland sources (agricultural, forested, and developed soils) and channel (stream banks and beds). Samples were sieved into fine (<63μm) and coarse (>63μm) fractions and analyzed for Mehlich-3 extractable elements, heavy metals, nutrient concentrations, as well as DNA sequencing for sediment microbes. Two publicly available fingerprinting toolkits (Sed_SAT, SourceTracker) were used to generate sediment mixing models. Nutrient concentrations in stream bank legacy sediments were significantly lower (1.6 ± 1.3% C, 0.1 ± 0.07% N, 0.05 ± 0.01% P) compared to upland forested, agricultural, and urban sediments (6.2 ± 4.7% C, 0.36 ± 0.23% N, 0.1 ± 0.04% P). However, fingerprinting models suggest that stream banks contribute 25-50% of suspended sediment and nutrient yields in the watershed, which vary from storm to storm. This study emphasizes the importance of legacy sediments on watershed sediment and nutrient exports, and the need to include them in water quality and TMDL assessments.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H51D..03J
- Keywords:
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- 1803 Anthropogenic effects;
- HYDROLOGYDE: 1813 Eco-hydrology;
- HYDROLOGYDE: 1871 Surface water quality;
- HYDROLOGYDE: 1879 Watershed;
- HYDROLOGY