Sediment budgets, estuarine sediment loads, and wetland sediment storage at watershed scales, York River watershed, Virginia.

摘要

Three separate but related aspects of sediment allocation in a river/estuarine system were examined. The main purpose was to compare sediment budgets for a series of eleven nested sub-watersheds as a function of watershed size, ranging from 65 to 6900 km2. The approach quantified six budget components: upland erosion; stream bank erosion; colluvial storage; wetland storage; stream channel erosion and storage; and sediment flux at the outlets. Three budgets were developed for each sub-watershed to examine the relative proportions of budget components, budget sensitivity (the influence of individual components on the overall budget), and the uncertainty of budget components. The study area was the rural, forested, low relief York River watershed in southeastern Virginia.; The relative proportions of budget components do not change with sub-watershed size. Budgets are more influenced by the tributary system than by the sub-watershed size. The budget is sensitive to most components because they are large in size and are highly variable. The uncertainties of budget components are proportional to the magnitude of the best estimates. Management efforts should focus on locally-derived sediment to improve water quality because little sediment from the upper parts of the watershed reaches the estuary.; Sediment loads were needed in the sediment budgets for three estuarine sampling stations. The loads were estimated by separating the gravitational circulation, tidal pumping, and river input components of long-term total suspended solids data. The load for the station closest to the river mouth was somewhat larger than literature values. The contribution to the estuary of the two tributary stations was previously unknown. Tidal pumping, rather than gravitational circulation, is the dominant process moving suspended sediment up the estuary.; The potential supply and storage of sediment in wetlands at the watershed level was examined by quantifying the areal extent of wetland type and location in the watershed, and surrounding land use, slope, and soil type. Results showed that these landscape characteristics are unevenly distributed within the York River watershed and its subdivisions. The differences in landscape characteristics between subdivisions suggest that wetland performance and its impact on water quality may vary within a watershed. Separate management approaches may be needed to accommodate these differences.