THE EFFECTS OF ROAD SALT DEICERS ON REDOX STRATIFICATION AND SALINIZATION OF EUTROPHIC LAKES IN SOUTHWEST MI, USA

Eutrophication in lakes can be caused by agricultural and residential runoff, due to an excess of nutrients, particularly phosphorus and nitrogen. Previous studies suggest that seasonal applications of the road salt deicers result in the increase of chloride concentrations which may impact lake aquatic ecosystems and geochemistry. The goal of this study is to examine the effects that road salt deicers have on the geochemistry of Woods and Wintergreen Lake, two kettle lakes located in Southwest MI, USA. Woods Lake is located in urban Kalamazoo, MI it has a surface area of ~ 9.7 ha and a max depth ~ 14m. Wintergreen Lake is located in rural Augusta, MI, has a surface area of ~16.4 ha and a max depth of ~ 7.9 m. Water column samples were collected during May, June, September, November, and December at 1 m intervals, using a van Dorn sampler. The water samples were filtered with two samples from each depth acidified and two un-acidified, and analyzed colorimetrically for Fe²⁺, Mn²⁺, total alkalinity, ΣNH₄⁺, and ΣPO₄^3-, by IC for anions (Cl^-_, Br^-, NO₃^-, SO₄^2-, F^-, PO₄^3-), and by ICP-OES for major ions and trace metals (Ca, Mg, K, Na, Co, Cd, Zn, Ni, Al). Using an YSI 650MDS/600QS probe, pH, temperature, dissolved oxygen, and conductivity were measured in situ at 0.5 m intervals. Nutrient and redox-sensitive species profiles demonstrate that both Woods and Wintergreen Lake are eutrophic, in agreement with results reported in prior studies. In Woods Lake, DO drops from >100% sat in the epilimnion to < 2% in the hypolimnion. In fall, as DO decreases, dissolved Fe²⁺, Mn²⁺, ΣNH₄⁺, and ΣPO₄^3- increase below 8 to 12 m depth, reaching ~230, ~50, ~950, and ~65 µM, respectively. Conductivity increases from 475 µS/cm at the surface to >1000 µS/cm which suggests salinity is contributed from road salt inputs. DO similarly decreases from >100% sat at the surface to ~4% in the bottom waters of Wintergreen Lake during the summer. In contrast, in fall, it is ~86% at 6 m. In summer, dissolved Mn²⁺ and ΣNH₄⁺ are present at Wintergreen Lake, but smaller concentrations (16 and ~25µM, respectively, at 5 m) compared to Woods Lake. Conductivity is much lower than at Woods Lake, increasing slightly from ~237 µS/cm in the epilimnion to ~392 µS/cm at 6 m. Continued sampling will be used to assess seasonal changes in lake stratification and to determine whether these two lakes are dimictic.