Water-quality variations in a forested Piedmont catchment, Georgia, USA
1994
Variations in runoff water quality were investigated at the Panola Mountain Research Watershed (PMRW), a 41 ha forested catchment in the Georgia Piedmont, from October 1985 to September 1988, to evaluate processes controlling solute transport. Routine weekly manual sampling was augmented by sampling during storms using a computer-controlled automatic water-quality sampler. Runoff from a 3 ha bedrock outcrop in the headwaters typically had high solute concentrations at the onset of a rainstorm. The SO4(-2) and H(+) concentrations were higher in runoff from this outcrop than in the corresponding rain. These high concentrations were attributed to the wash-off of acidic-SO4(2-) dry deposition that had accumulated on the outcrop during the preceding dry period. In contrast, both NH4(+) and NO3(-1) were depleted in the runoff, probably because they were removed by the lichens and mosses covering the outcrop. Storm sampling of streamwater at the basin outlet indicated that NO3(-1) was mobilized during some summer storms, particularly in late July of each year. Also, SO4(2-) and alkalinity varied markedly during storms. As determined from the routine weekly sampling, the streamwater was sufficiently neutral to indicate that streamwater acidification by acidic atmospheric deposition was relatively unimportant: only 26% of the decrease in alkalinity was associated with SO4(2-) concentration increases. The storm data, however, indicated that streamwater acidification did not occur during the storms sampled, but that the median alkalinity was much lower and SO4(2-) concentrations were much higher than values determined from the weekly (base flow) sampling. The storm-sampling results indicate that episodic acidification may occur at PMRW.
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