WATER-QUALITY VARIATIONS IN A FORESTED PIEDMONT CATCHMENT, GEORGIA, USA

Variations in runoff water quality were investigated at the Panola Mou ntain Research Watershed (PMRW), a 41 ha forested catchment in the Geo rgia Piedmont, from October 1985 to September 1988, to evaluate proces ses controlling solute transport. Routine weekly manual sampling was a ugmented by sampling during storms using a computer-controlled automat ic water-quality sampler. Runoff from a 3 ha bedrock outcrop in the he adwaters typically had high solute concentrations at the onset of a ra instorm. The SO42- and H+ concentrations were higher in runoff from th is outcrop than in the corresponding rain. These high concentrations w ere attributed to the wash-off of acidic-SO42- dry deposition that had accumulated on the outcrop during the preceding dry period. In contra st, both NH4+ and NO3- were depleted in the runoff, probably because t hey were removed by the lichens and mosses covering the outcrop. Storm sampling of streamwater at the basin outlet indicated that NO3- was m obilized during some summer storms, particularly in late July of each year. Also, SO42- and alkalinity varied markedly during storms. As det ermined from the routine weekly sampling, the streamwater was sufficie ntly neutral to indicate that streamwater acidification by acidic atmo spheric deposition was relatively unimportant: only 26% of the decreas e in alkalinity was associated with SO42- concentration increases. The storm data, however, indicated that streamwater acidification did not occur during the storms sampled, but that the median alkalinity was m uch lower and SO42- concentrations were much higher than values determ ined from the weekly (base flow) sampling. The storm-sampling results indicate that episodic acidification may occur at PMRW.