HYDROGEOCHEMICAL CONTROLS ON MINERAL WEATHERING AND MASS TRANSPORT IN A FORESTED WATERSHED, UPPER JAMES RIVER, VIRGINIA
The initial focus of this research is to identify the geochemical regularities and differences in the carbonic acid system, elemental concentrations, and mineral equilibria between surface waters and shallow groundwaters along with soil weathering contributions to the drainage. Streams were sampled for field parameters and aliquots were preserved for laboratory analysis of cations (ICP), anions (IC), and for titration alkalinity. Discharge was measured and pulled from USGS gage locations on selected streams to characterize the elemental fluxes from subcatchments of the Upper James River watershed. Seasonal changes and long term trends in the hydrogeochemistry of the Upper James River are investigated by comparing historical data for the watershed obtained from USGS gages. Soil samples were collected from forested regions over representative lithologic units in the watershed and leached to determine the readily soluble hydroxides and carbonates. This allows for endmember characterization of the siliclastic and carbonate lithologies and in the determination of their contribution to the hydrogeochemistry and elemental fluxes from the watershed.
Preliminary data show that smaller streams within the drainage have HCO3 concentrations and elemental chemistries that are consistent with the catchment lithologies. The larger streams show evidence of anthropogenic pollution such as high Na, Cl and SO4 concentrations. Long term data from USGS gauging stations show an inverse relationship between elemental concentrations and discharge.