The Chemical Composition of Lakes in the North-Central United States

Authors

Eville Gorham, Department of Ecology and Behavioral Biology, University of Minnesota, Minneapolis 55455
Walter E. Dean, U.S. Geological Survey, Denver, COFollow
Jon E. Sanger, Department of Botany and Bacteriology, Ohio Wesleyan University, Delaware 43015

Document Type

Article

Date of this Version

3-1983

Comments

Published in Limnology and Oceanography, Vol. 28, No. 2 (Mar., 1983), pp. 287-301.

Abstract

Lake waters of the north-central U.S.A. are classified into five groups, based on increasing specific conductivity and changes in ionic composition from east to west, from Wisconsin through Minnesota to North and South Dakota. The most dilute group of waters has specific conductivities <29 μnhos x cm^-1 at 25°C; the most concentrated group has specific conductances that range from 7,000 to 73,000 μmhos. As conductivity increases all major ions increase, but there is a shift in cation dominance from Ca²⁺ to Mg²⁺ to Na⁺, and in anion dominance from HCO₃^- to SO₄^2-. This shift partly reflects a westward increase in climatic aridity, and partly a westward sequence of glacial drifts from noncalcareous to calcareous and thence to calcareous with abundant sulfur-bearing minerals. Levels of pH, K, Cl, F, B, and SiO₂also show a distinct westward increase. Concentrations of NO₃^- and Mn increase from east to west, but the trend is less distinct. Concentrations of Fe vary widely without any trend over the range of conductivity. Color, mostly from dissolved organic matter, is controlled chiefly by lake depth, except for lakes with extensive peatlands in their drainage basins.