EFFECTS OF ROAD SALT DEICERS ON EUTROPHICATION AND SALINIZATION OF THREE KETTLE LAKES IN SOUTHWEST MI, USA

In recent years, increasing evidence suggests that the application of road salt deicers significantly impacts the biogeochemistry of inland lakes. For example, input of chloride ions may change the density structure of lakes, inhibiting seasonal turnover and causing a transition from dimixis to meromixis. In this study, the geochemistry and mixing of Woods Lake (urban Kalamazoo, MI,), Wintergreen Lake (rural Augusta, MI), and Lawrence Lake (rural Barry Township, MI) was assessed. In May, June, July, September, November and December water column samples were collected at 1 m intervals, in the deepest part of each lake (14m in Woods Lake; 7.4m in Wintergreen Lake; 12.5m in Lawrence Lake). The samples were filtered (0.45 µm) and analyzed colorimetrically for Fe²⁺, Mn²⁺, total alkalinity, ΣH₂S, ΣNH₄⁺, and ΣPO₄^3-; by IC for Cl^-, SO₄^2-, and PO₄^3-; and by ICP-OES for Ca, Mg, Na, and K. A YSI multi-parameter probe was used to measure pH, temperature, conductivity, and dissolved oxygen in situ at 0.5 m intervals. Nutrient and redox-sensitive species profiles demonstrate that Woods and Wintergreen Lake are eutrophic, which is consistent with prior studies. DO typically decreases from >100% at the surface to ~2% in the hypolimnion of Woods Lake, whereas conductivity increases from ~400 µS/cm at the surface to ~1000 µS/cm in the hypolimnion. As lake waters become anoxic, Fe²⁺, Mn²⁺, ΣNH₄+, and ΣPO₄^3- levels increase. In Wintergreen Lake, DO decreases from >100% at the surface to <4% during the spring but remains near ~86% throughout the water column in the fall. The conductivity increases to 472 µS/cm in spring 2012 and is close to 208 µS/cm throughout the lake column in fall 2012. In spring 2013, it returned to similar conditions as the previous year suggesting that Wintergreen Lake is dimictic. Woods Lake contains a significantly larger amount of Cl^- than either of the rural lakes, averaging 301 ppm at 11m, suggesting that it has been impacted by inputs from road salt deicers. Chloride levels correlate with conductivity, such that Woods Lake is denser in the hypolimnion, which may inhibit seasonal lake turnover. In contrast, Wintergreen and Lawrence Lake have an average Cl^- conc. of 15 and 8ppm, respectively, changing little with depth. This study suggests that road salt deicers can greatly impact the geochemistry and mixing of urban lakes.