Over 317,000 tonnes of road salt (NaCl) are applied annually for road deicing in the Twin Cities Metropolitan Area (TCMA) of Minnesota. Although road salt is applied to increase driving safety, this practice influences environmental water quality. Thirteen lakes in the TCMA were studied over 46 months to determine if and how they respond to the seasonal applications of road salt. Sodium and chloride concentrations in these lakes were 10 and 25 times higher, respectively, than in other non-urban lakes in the region. Seasonal salinity/chloride cycles in the lakes were correlated with road salt applications: High concentrations in the winter and spring, especially near the bottom of the lakes, were followed by lower concentrations in the summer and fall due to flushing of the lakes by rainfall runoff. The seasonal salt storage/flushing rates for individual lakes were derived from volume-weighted average chloride concentration time series. The rate ranged from 9 to 55% of a lake's minimum salt content. In some of the lakes studied salt concentrations were high enough to stop spring turnover preventing oxygen from reaching the benthic sediments. Concentrations above the sediments were also high enough to induce convective mixing of the saline water into the sediment pore water. A regional analysis of historical water quality records of 38 lakes in the TCMA showed increases in lake salinity from 1984 to 2005 that were highly correlated with the amount of rock salt purchased by the State of Minnesota. Chloride concentrations in individual lakes were positively correlated with the percent of impervious surfaces in the watershed and inversely with lake volume. Taken together, the results show a continuing degradation of the water quality of urban lakes due to application of NaCl in their watersheds.
Bibliographical noteFunding Information:
We acknowledge and thank the Minnesota Local Road Research Board (LRRB) and the Minnesota Department of Transportation (Mn/DOT) for providing the funding for this research. We also thank the Technical Advisory Panel, lead by Wayne Sandberg of Washington County, for input and suggestions to our research. We thank Amy Myrbo and Kristina Brady of the Limnological Research Center (LacCore Facility) at the University of Minnesota, Department of Geology and Geophysics, for providing equipment and expertise for the extraction and sectioning of the lake sediment cores. Karen Jensen of the Metropolitan Council (MCES) provided valuable information on lake watershed delineations and water quality information.
Copyright 2009 Elsevier B.V., All rights reserved.
- Lake chemistry
- Northern climate
- Road salt
- Urban area
- Water Quality
Continental Scientific Drilling Facility tags