WHY HAVE LAKE ERIE CHLORIDE CONCENTRATIONS DECREASED?

Abstract

Since the turn of the century, chloride concentrations in Lake Erie have risen from approximately 7 mg/L to approximately 35–45 mg/L in the late 1960’s. However, since the late 1960s, chloride concentrations have decreased to approximately 15–20 mg/L. In order to gain a quantitative understanding of this recent decreasing trend, this paper evaluates the available historical chloride loading data from the major industrial point sources along the Detroit River (which accounts for 94% of the inflow to Lake Erie). Since the 1960s five of the six major industrial point sources have either ceased the production of soda ash by the Solvay method or ceased the manufacture of various inorganic chemicals by chlor-alkali methods. This has resulted in a decrease in chloride loadings to the Detroit River of 4,680 tonnes/day. In 1967, this accounted for 53.5% of the total chloride loadings from Detroit River point and nonpoint sources and 36% of the total chloride input from the Detroit River to Lake Erie. The substantial reductions in chloride loadings resulting from these changes in industrial operations demonstrate the importance of process change when dealing with polluting substances which cannot be treated at a realistic cost.