THE EFFECTS OF ROAD SALT ON ASYLUM LAKE GEOCHEMISTRY

Asylum Lake is a 19.8 ha kettle lake located in Kalamazoo, MI near three major roadways, thus it is expected to receive runoff with significant concentrations of road salts in winter and spring. Road salts contribute unreactive Cl^-to surface and groundwaters, which can accumulate and significantly increase water density. Typical lakes in Michigan experience turnover events in fall and spring, during which water from the epilimnion is mixed with water from the hypolimnion. With enough of an increase in water density, lake turnover events may be delayed or prevented (e.g. Wetzel, 2001, Limnology). The objective of this study is to determine if road salts in Asylum Lake are preventing turnover events and, if so, how this changes the lake geochemistry.

Lake water column samples have been collected monthly at the deepest point in the lake, beginning in September 2012; sampling will continue for one year. In situ measurements of dissolved oxygen (DO), conductivity, temperature, and pH are measured at .5 m intervals. Four water samples per 1 m depth are collected at 1m intervals, filtered (.2 µM), and two are preserved with HNO₃. Samples are immediately analyzed upon return to the lab for Fe²⁺, Mn²⁺, PO₄^3-, NH₄⁺, alkalinity, and H₂S via colorimetry. Within one week of collection, samples are analyzed on an ICP-OES for Ca²⁺, Mg²⁺, K⁺, and Na⁺. Within two weeks, samples are analyzed for Cl^- on an ion chromatograph and for SO₄^2-via a turbidity technique.

Data thus far shows Asylum Lake to be a eutrophic lake with anoxic benthic waters throughout summer and early fall. In the anoxic hypolimnion, there is a build-up of NH₄⁺, Mn²⁺, PO₄^3-, and H₂S to levels as high as 220, 40, 11, and 87 µM, respectively, but Fe²⁺ levels are always at or below detection limits of 3.5 µM. Concentrations of Cl^-reach up to 180ppm. Conductivity increases with depth in the summer and fall but becomes nearly constant during one sampling event in early winter. On this date, temperature and DO also vary much less with depth, which suggests that fall turnover occurred, but was significantly delayed.