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The Contribution of Red Clay Erosion to Orthophosphate Loadings into Southwestern Lake Superior¹

ABSTRACT

The effects of the erosion of red clay deposits along the northwestern Wisconsin shoreline area on orthophosphate inputs into Lake Superior was investigated. Using clay soil and river particulate samples, the release of orthophosphate in Lake Superior water was studied. The results indicate a maximum release of 240 metric tons of soluble PO₄ from soil entering Lake Superior annually from shoreline erosion and 63 metric tons of PO₄ from river particulates. These estimates assume equilibrium with soluble orthophosphate at a concentration of < 0.005 mg/liter of PO₄, which is typical of Lake Superior water. Actual PO₄ release may be less because soluble orthophosphate concentrations are higher in near shore waters. Suspended particulates buffer soluble orthophosphate concentrations and may even cause a net removal of orthophosphate from Lake Superior water when high concentrations exist.

Key Words: soil dissolution • phosphate sorption • particle-size distribution • river particulates

¹ Contribution from the Dep. of Chemistry and Center for Lake Superior Environ. Studies (CLSES), Univ. of Wisconsin-Superior, WI 54880 (CLSES Periodical Contribution no. 18). Research support from the Univ. of Wisconsin Sea Grant Program and EPA Grant no. R005169-01 is gratefully acknowledged. This work was presented, in part, at the 18th Conf. on Great Lakes Res., Int. Conf. for Great Lakes Res., Albany, N. Y., 20 May 1975.

² Associate Professor of Chemistry, Dep. of Chemistry, Univ. of Wisconsin-Superior.

Received for publication August 17, 1976.