THE INFLUENCE OF ROAD SALT DEICERS ON URBAN KETTLE LAKES (Invited Presentation)

The use of NaCl and CaCl₂ to deice winter roads has led to significant salinization of groundwater and surface water in the US, Canada and elsewhere. Increased concentrations of chloride in aqueous systems can result in chronic or acute toxicity to freshwater organisms; contamination of drinking water supplies; increased toxicity of heavy metals; damage to structures such as bridges and automobiles; increases in invasive species; and changes in the chemistry and density structure of lakes. The water column chemistry of four natural kettle lakes, two urban (Woods Lake and Asylum Lake) and two rural (North Lake and Brewster Lake) located in southwest Michigan was monitored to assess the influence of road salt contamination on the physical mixing and redox stratification of eutrophic urban lakes. Woods Lake (max depth ~14 m) is a natural kettle lake with no natural surface water inlets or outlets, but with runoff input via stormwater sewers. Road salt accumulation appears to have led to a state of cultural meromixis in Woods Lake, which has a persistently anoxic, redox-stratified hypolimnion with accumulation of high concentrations of dissolved sodium, chloride, Fe(II), phosphate, ammonium and methane. Asylum Lake (max depth ~ 16 m) is a groundwater fed kettle lake with maximum chloride levels exceeding those at Woods Lake. However, Asylum Lake appears to be monomictic, likely due to a shorter residence time of water compared to Woods Lake. The hypolimnion of Asylum Lake also has high concentrations of dissolved sodium, chloride, phosphate, ammonia and methane, but Fe(II) is always below detection limits. North and Brewster Lakes (max depth ~20 and 9 m, respectively), which are located in rural settings, have chloride levels ~200 times lower than those in Woods and Asylum Lakes. Ongoing studies are investigating seasonal mixing in North Lake as well as seasonal changes in water column methane levels and microbial community structure in Woods, Asylum and North Lakes.