Seasonal patterns of mineral and organic acidification in two streams in Southwestern Nova Scotia

DOC concentrations in two streams of different hydrologic order are highly variable with the higher order stream exhibiting approximately a 3 mo response lag. Seasonal variation of SO⁴ concentration and flux are similar in both streams and do not reflect the seasonal patterns in precipitation. The basins store SO₄ from May to November and lose SO₄ from December to April. Consequently, SO⁴ concentrations and flux are maximum during January to March and reach a minimum during July to September. The highly organic lower order stream exhibits relatively stable pH controlled by two competing mechanisms. The pH is dominated by organic acids during the summer and autumn and by mineral acids during the late winter and early spring. In the higher order system, the pH tends to be inversely related to changes in SO₄ concentration. These observations suggest that organic systems do respond to acidic deposition but that in some systems mineral acid influence may be restricted to the winter and spring.