EUTROPHICATION AND SALINIZATION OF WOODS LAKE, KALAMAZOO, MI

The progressive eutrophication of lakes through anthropogenic corridors is of growing concern, particularly in areas of high population density. The perpetual application of road deicing salts can exacerbate eutrophication through the elevation of chloride concentrations; elevated chloride levels in monimolimnetic waters may lead to persistent density stratification (i.e. meromixis), stable anoxia in bottom waters, and biological dependence on episodic nutrient loading. The goal of this study is to examine the influence of nutrient and road salt influx on water quality in Woods Lake, a small, glacial lake in urban Kalamazoo, MI. Water samples were collected at 1 m intervals between May and July 2010, generally during midday, using a van Dorn sampler. Four replicate 20 mL aliquots were taken every meter and passed through 0.45 µm syringe filters. Two samples were acidified using two drops of concentrated HNO₃ while two were left unacidified. Temperature, pH, conductivity, and dissolved oxygen (DO) values were obtained in situ using a YSI 650MDS/600QS multiparameter sonde. Laboratory samples were analyzed colorimetrically for Fe²⁺, total alkalinity, ΣNH₄⁺, and Mn²⁺, by IC for anions (F^-, Cl^-, Br^-, NO₃^-, NO₂^-, PO₄^3-, and SO₄^2-), and by ICP-OES for major ions (Mg, Ca, K, Na). Redox sensitive species and nutrients demonstrate that the lake is eutrophic with significant redox stratification of the lake column waters. DO drops from >100% sat near the surface to <4% sat at ~5 m. Similarly, pH drops from ~8.2 at the surface to ~6.5 at 10 m, while Fe²⁺ and Mn²⁺ increase from below detection limits to >250 µM and > 65 µM at ~12 m, respectively. In the bottom waters (~12 m) DO, temperature, and pH readings typically reach values of ~1% sat, ~5˚C, and 6.5, respectively, while Mn²⁺, NH₄⁺, and Fe²⁺ concentrations were found to be > 60, >650, and >200 µM, respectively. Woods Lake has been significantly salinized by road salt input; conductivity levels increase from ~450 µS/cm at the surface to >1000 µS/cm at ~10 m, concomitant with a Cl^- increase from ~100 ppm in the upper 3 m, to levels between 250-400 ppm at depth. These data clearly indicate that Woods Lake water quality has been greatly influenced by inputs of both nutrients and salt, leading to persistent eutrophy, redox stratification, and potential density stratification as well.