Cultural meromixis: Effects of road salt on the chemical stratification of an urban kettle lake

Saline runoff from application of road salt deicers has the potential to create persistent density gradients in urban freshwater lakes, resulting in significant changes to physical mixing and biogeochemical cycling. In this study, the seasonal influence of road salt influx on the geochemical cycling of a small, urban kettle lake is examined. Water column samples were collected approximately twice per month for fifteen months and analyzed for temperature, pH, conductivity, major ions, nutrients and redox-sensitive solutes. The lake water column was redox-stratified with high concentrations of dissolved Mn(II), Fe(II), ammonium, phosphate and, during some periods, sulfide and methane in the hypolimnion. Bottom water anoxia was persistent throughout the entire sampling period. Concentrations of sodium and chloride, which correlated strongly with conductivity, were over a hundred times greater compared with levels in nearby rural lakes. Conductivity, chloride and calculated density profiles indicated the presence of a pycnocline at ~ 9 m depth that persisted throughout the sampling period. The chemical data demonstrate that road salt input has caused the lake to become meromictic, with a complete lack of fall and spring turnover.