LEGACY SEDIMENT CHEMISTRY AND LAND USE: USING SMALL CATCHMENT BASINS TO DETERMINE POTENTIALLY HARMFUL INPUTS TO DOWNSTREAM ENVIRONMENTS

Tens of thousands of mill dams documented by Walter and Merritts (2008) impound millions of cubic meters of sediment containing the runoff from hundreds of years of land use in the Piedmont and Ridge and Valley provinces of the eastern US. Because land use in most catchments is not spatially uniform comparing natural background chemistry of a legacy deposit from chemical and physical weathering processes of parent rock and upland soils sources from anthropogenically-induced land use sources such as agriculture or urban development over time is problematic. The upper reach of the Yellow Breeches Creek (Cumberland County, PA) watershed provides an opportunity to determine background and anthropogenically added major and trace elements due to distinctive spatial land use distribution with common parent and upland soil characteristics from two sub-basins. Cores from two legacy sediment deposits within connected sub-watersheds of the Yellow Breeches Creek watershed: Mountain Creek (MC), predominately forested land use and the upper reach of the Yellow Breeches Creek (YBC) proper, predominately agricultural land use are used to show chemical changes in deposited sediment post settlement. Major elements show little change in concentration over time in both sites except for phosphorus, which shows a 4-5 fold increase toward the present in the YBC deposit. Trace metals of Cu, Ni, Zn, and Pb increase 2-3 fold over background in the YBC deposit most likely from excessive use of fertilizers, herbicides, and other soil amendments in the past. These pollutants are and will continue to be available for remobilization as mill dams are removed or are breached. Preliminary analysis of suspended sediment fluxes directly above and below these deposits also shows a significant increase in phosphorus and trace metals. These underestimated additional fluxes of phosphorus, trace metals (and presumably nitrate nitrogen) to downstream environments including the Chesapeake Bay may explain increases in hypoxia in the recent years despite efforts to control agricultural non-point source inputs of nutrients.