A COMPARATIVE ANALYSIS OF THE EFFECTS OF FORESTED BUFFERS AND FLOODPLAIN SOIL PROPERTIES ON PHOSPHOROUS DYNAMICS IN TWO CHESAPEAKE BAY SUB-WATERSHEDS, VIRGINIA

Aquatic ecosystems are known to undergo fluctuations in nutrient and other contaminant levels as a function of both natural processes and anthropogenic stresses. The historical changes in environmental conditions related to nutrient and sediment fluxes in the Chesapeake Bay, eastern USA, are well documented. However, changes in both extrinsic and intrinsic floodplain processes necessitate constant monitoring as modern climate and anthropogenic alterations exert new pressures to the basin. We report an ongoing analysis of stream water and riparian zone soil phosphorous (P) dynamics in two 3^rd order sub-watersheds in central and northern Virginia. The Ni River in central Virginia is a relatively pristine (70% forested) sub-watershed of the Rappahannock River basin, which is the largest contributor of sediment per square kilometer to the Chesapeake Bay; Sugarland Run located in the suburbs of Washington D.C., is a more human impacted (14% forested, > 45% impervious surfaces) sub-watershed of the Potomac River, the second largest contributor of sediment to the Chesapeake Bay.

Total stream P concentrations were measured during both high and low flows and Mehlich-3 methods were used to evaluate both surficial and sub-surface P fluxes from riparian soils into the two stream systems. Preliminary results show total P levels in Sugarland Run range from 30-200 ppb, with an average of 53.84 ppb. In contrast, the more pristine Ni River P concentrations are typically <10 ppb. Our ongoing Mehlich-3 based analysis of floodplain P will highlight the forms of P in alluvial soils of the region and the role of adsorption/desorption on the overall P dynamics in these watersheds. Analyses of stream bank erosion will also help in quantifying the proportion of total P additions derived from erosion of previously deposited legacy sediments.