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

Abstract

AbstractThe 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.