Microbial consumption of nitric and sulfuric acids in acidified north temperate lakes1

Rates of sulfate reduction and denitrification were measured in the sediments of unacidified, experimentally acidified, and atmospherically acidified lakes in North America and Norway. These data, plus profiles of porewater and sediment chemistry, demonstrated that in all of the lakes H was being actively consumed by both sulfate reducers and denitrifiers. Both of these microbial activities were assayed in sediments overlaid by oxygenated water, demonstrating that anoxic hypolimnia are not required for in situ alkalinity production. Neither short term experimental acidification nor long term atmospheric acidification had detectably inhibited the activity of these two types of bacteria. Both processes were active at pH 4.5. In lakes that were receiving significant quantities of both nitric and sulfuric acids, short term H + consumption from denitrification was 1.5–2 times faster than H consumption by sulfate reduction. However on an annual basis, because of loss of reduced sulfur during fall and winter, long term H + consumption by denitrification was estimated to be 4–5 times as large as H + consumption by sulfate reduction.