HR: 17:00h
AN: H54A-04    [Abstracts]
TI: Sediment Yields and Sediment Sources in the Chesapeake Bay Watershed
AU: * Gellis, A C
EM: agellis@usgs.gov
AF: U.S. Geological Survey, 8987 Yellow Brick Road, Baltimore, MD 21237
AU: Landwehr, J M
EM: jmlandwe@usgs.gov
AF: USDA-Agricultural Research Service, BARC-West Bldg-007, Beltsville, MD 20705
AU: Pavich, M J
EM: mpavich@usgs.gov
AF: U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, VA 20192
AU: Hupp, C R
EM: crhupp@usgs.gov
AF: USDA-Agricultural Research Service, BARC-West Bldg-007, Beltsville, MD 20705
AU: Ritchie, J C
EM: jritchie@hydrolab.arsusda.gov
AF: USDA-Agricultural Research Service, BARC-West Bldg-007, Beltsville, MD 20705
AU: Reuter, J M
EM: Joanna.Reuter@uvm.edu
AF: University of Vermont, Delehanty Hall,˙Colchester Avenue, Burlington, VT 05405
AB: Fine-grained sediment is having an adverse effect on the living resources and habitat of the Chesapeake Bay and its watershed. In order to reduce sediment inputs to the Bay, it is necessary to quantify erosion rates and sediment yields and identify the significant sources of fine-grained sediment. Sediment sources in the Chesapeake Bay watershed were identified using different methods at several scales. At the Chesapeake Bay scale (165,800 km²), U.S. Geological Survey suspended-sediment data collected from 1985 through 2001 for 35 stations showed that 4 of the 6 highest sediment yields were in the Conestoga River Basin, Pennsylvania, which drains to the Susquehanna River. In the Susquehanna River Basin (70,190 km²), erosion rates were determined using atmospheric ¹⁰Be at 92 river outlets and confirmed that the highest rates of erosion were in the Conestoga River Basin. In three small watersheds draining to the Chesapeake Bay -- the Pocomoke River (157 km²), Little Conestoga Creek (109 km²), and Mattawoman Creek (142 km²) -- sediment sources were identified using a sediment-fingerprinting approach. In this approach, the sources of fine-grained suspended sediment in transport can be established by comparing physical and chemical properties of the suspended sediment to potential sources. In this study, suspended sediment (< 0.062 mm) collected during storm runoff was compared to upland sediment sources (cropland, construction sites, and forest) and channel corridor sources (channel banks and bed) using radionuclides (²¹⁰Pb, ¹³⁷Cs), stable isotopes (¹³C, ¹⁵N), and total C, N, and P. Preliminary results are available for two of the three watersheds. In the Pocomoke River watershed, ditch beds which were dug to drain cropland are a significant source of sediment. In the Little Conestoga Creek watershed, river banks and cropland are significant sources Erosion rates for nine cropland sites in the Little Conestoga Creek watershed were also determined with ¹³⁷Cs inventories and indicated an average rate of erosion of 16.4 tons/hectare/year, which is about 25 times the sediment yield of the Little Conestoga Creek (0.65 tons/hectare/year). This finding indicates substantial sediment storage in the watershed.
DE: 1815 Erosion
DE: 1825 Geomorphology: fluvial (1625)
DE: 4558 Sediment transport (1862)
SC: Hydrology [H]
MN: Fall Meeting 2005