Effects of road salt deicers on an urban groundwater-fed kettle lake

Abstract

Road salt deicers significantly influence the chemistry and physical mixing of urban lakes, even causing transition from dimixis to monomixis or meromixis. In this study, the water column geochemistry of Asylum Lake, a primarily groundwater-fed, eutrophic kettle lake in urban Kalamazoo, MI, was monitored for over a year to determine the extent of road salt deicer influence on the lake chemistry and the physical mixing of the lake. Water column samples from the surface to the deepest part of Asylum Lake were analyzed monthly for nineteen months for a suite of parameters including dissolved oxygen, pH, conductivity, temperature, alkalinity, Fe2+, Mn2+, orthophosphate, total NH4+, alkalinity, total sulfide, Cl−, SO42−, Ca2+, Mg2+, K+, and Na+. During the study period, spring mixing was never observed and a nearly complete fall turnover was observed only in November 2013. The hypolimnion of Asylum Lake was always hypoxic or anoxic and redox-stratified, with seasonal development of suboxic and sulfidic zones, which were disrupted in fall and winter following partial fall turnover and subsequent ice cover. This study suggests that road salt deicers have caused Asylum Lake to transition from dimixis to meromixis or periodic monomixis with significant consequences for biogeochemical cycles in the lake waters.