Comparisons of watershed sulfur budgets in southeast Canada and northeast US: new approaches and implications

Abstract

Most of eastern North America receives elevated levels of atmospheric deposition of sulfur (S) that result from anthropogenic SO2 emissions from fossil fuel combustion. Atmospheric S deposi- tion has acidified sensitive terrestrial and aquatic ecosystems in this region; however, deposition has been declining since the 1970s, resulting in some recovery in previously acidified aquatic ecosystems. Accurate watershed S mass balances help to evaluate the extent to which atmospheric S deposition is retained within ecosystems, and whether internal cycling sources and biogeochemical processes may be affecting the rate of recovery from decreasing S atmospheric loads. This study evaluated S mass balances for 15 sites with watersheds in southeastern Canada and northeastern US for the period 1985 to 2002. These 15 sites included nine in Canada (Turkey