Atmospheric deposition effects on the chemistry of a stream in Northeastern Georgia

Abstract

The quantity and quality of precipitation and streamwater were measured from August 1985 through September 1986 in the Brier Creek watershed, a 440-ha drainage in the Southern Blue Ridge Province of northeastern Georgia, to determine stream sensitivity to acidic deposition. Precipitation samples collected at 2 sites had a volume-weighted average pH of 4.40 whereas stream samples collected near the mouth of Brier Creek had a discharge-weighted average pH of 6.70. Computed solute fluxes through the watershed and observed changes in streamwater chemistry during storm flow suggest that cation exchange, mineral weathering, SO42− adsorption by the soil, and groundwater discharge to the stream are probable factors affecting neutralization of precipitation acidity. Net solute fluxes for the watershed indicate that, of the precipitation input, > 99% of the H+, 93% of the NH4+ and NO3−, and 77% of the SO42− were retained. Sources within the watershed yielded base cations, Cl−, and HCO3− and accounted for 84, 47, and 100% of the net transport, respectively. Although streamwater SO42− and NO3− concentrations increased during stormflow, peak concentrations of these anions were much less than average concentrations in the precipitation. This suggests retention of these solutes occurs even when water residence time is short.