Salinization: the ultimate threat to temperate lakes, with particular reference to Southeastern Wisconsin (USA)

Many lakes in Southeastern Wisconsin (the metropolitan-Milwaukee area) are gradually becoming increasingly “salty”. While these waterbodies would not be considered presently to be saline lakes, there has been a rapid increase in the chloride concentrations in most of these lakes over the last 30 years, with the lakes increasing from a mean chloride concentration of about 19 mg/L to over 100 mg/L in some cases. While ecological impacts can be expected when chloride values exceed 250 mg/L, the rate of increase presents a basis for concern, especially since the underlying geology of the region is based on limestone/dolomite which is deficient in chlorides. Thus, the origin of the chlorides is anthropogenic: human and industrial wastewaters (treatment of which has effected improvements in trophic status but has not affected other water-borne contaminants) and winter de-icing practices based upon large quantities of sodium chloride are major contributors to the increasing concentrations of chloride in the region’s waterways. Without taking remedial measures, the rate of salinization is expected to continue to increase, resulting, ultimately, in the alteration of the freshwater systems in the region.