COMPARISON OF SALINITY IN RURAL AND SUBURBAN LAKES OF SOUTHWEST MICHIGAN, USA

Increasing development and construction of roads in suburban and urban areas of the upper Midwest has led to increased use of road salt as a deicer. This road salt infiltrates into ground water with precipitation and snowmelt and enters lakes and rivers via groundwater and surface runoff. In glacial kettle lakes with little outflow, road salt may slowly accumulate with time. This is problematic, because high levels may be toxic to freshwater organisms and may prevent overturn of lakes, exacerbating eutrophication and creating persistent anoxia in bottom waters. In this study, it was hypothesized that greater concentrations of sodium and chloride would be present in a lake in an urban watershed compared to lake in a more isolated, rural area. Three lakes were chosen for study: Brewster Lake, a natural kettle lake and Aurohn Lake, a constructed lake, both located in rural Hastings, MI, as well as Asylum Lake, located in suburban Kalamazoo, MI. A van Dorn sampler was used to obtain water samples at ~1 m intervals from the surface to the deepest location of each lake (~16 m in Asylum Lake; ~8 m in Brewster Lake; ~3.5 m in Aurohn Lake). Replicate samples from each depth were immediately acidified with nitric acid and stored in HDPE vials. Samples were kept in a refrigerator prior to analyses via ion chromatography for a suite of anions (Cl^-, F^-, Br^-, NO₃^-, NO₂^-, SO₄^-2, PO₄^-3) and for major cations (Mg, Ca, Na, K) via ICP-OES. Asylum Lake contained significantly larger concentrations of chloride than either of the rural lakes, with an average chloride concentration of ~130 ppm. Chloride levels increased from ~100 ppm near the surface to >150 ppm at depth. In contrast, chloride levels were much lower in the rural lakes, averaging ~5 ppm in Brewster Lake and ~10 ppm in Aurohn Lake, and increased only slightly with depth, with maximum concentrations of 5.6 and 10.3 ppm, respectively. The dramatically different concentrations of chloride in these lakes supports the hypothesis that road salt use in developed areas has greatly impacted surface water quality.