Correlations between stream sulphate and regional SO2 emissions

The relationship between atmospheric SO₂ emissions and stream and lake acidification has been difficult to quantify, largely because of the limitations of sulphur deposition measurements. Precipitation sulphate (SO₄) records are mostly <5 yr in length¹ and do not account for dry sulphur deposition². Moreover, a variable fraction of wet- and dry-deposited sulphur is retained in soils and vegetation and does not contribute to the acidity of aquatic systems^3,4. We have compared annual SO₂ emissions for the eastern United States from 1967 to 1980 with stream SO₄ measurements from fifteen predominantly undeveloped watersheds (Figs 1,2). We find that the two forms of sulphur are strongly correlated on a regional basis and that streams in the southeastern United States (SE) receive a smaller fraction (on average, 16%, compared with 24% of regional sulphur emissions than do streams in the northeastern United States (NE). In addition to providing direct empirical evidence of a relationship between sulphur emissions and aquatic chemistry, these results suggest that there are significant regional differences in the fraction of deposited sulphur retained in basin soils and vegetation.