Implications of a gradient in acid and ion deposition across the northern Great Lakes states

Abstract

Average precipitation pH, 1979-1982, declines from west to east from 5.3 to 4.3 along a cross section of sites in Minnesota, Wisconsin, and Michigan. This answers questions about the seasonal and geographic pattern of anthropogenic acid precursor emissions and reaction products (SO/sub 4//sup 2 -/, NO/sub 3//sup -/, H/sup +/, NH/sub 2//sup +/) that increase from west to east. Except for higher concentrations of Ca/sup 2 +/ and Mg/sup 2 +/ observed at one site in the cultivated areas of southwestern Minnesota, the contribution of soil-related metal cations to the total ions in solution is small (17%) and relatively uniform across the region. Significant seasonal and geographic patterns in precipitation chemistry and deposition values are observed. Close correspondence of the sums of strong acid anions with the sums of hydrogen and ammonium ions in precipitation is observed, indicating anthropogenic sources of sulfur and nitrogen oxides. Present atmospheric inputs show close chemical correspondence when precipitation chemistry values are compared to the resulting ionic composition of weakly buffered lakes in north central Wisconsin and northern Michigan. The wet deposition of total acidity in the middle and eastern part of the region is comparable to that of impacted sites in the Adirondacks andmore » in regions of Scandinavia. 39 references, 3 figures, 6 tables.« less