EVALUATING THE INFLUENCE OF DE-ICING SALT ON WATER QUALITY OF OHIO RIVERS OVER TIME

Much of the impact on fresh water in the U.S. comes from non-point sources, with population density and/or land use playing an important role. Major anthropogenic inputs to surface waters are chloride and sodium, derived primarily from urban contributions such as road salt, and nitrate, primarily from agricultural sources such as fertilizers. Historic data were tabulated from a variety of sources to identify long-term trends in chloride, sodium, and nitrate concentrations in rivers at multiple locations throughout central Ohio, USA. In 2012-2013, a number of sites also were sampled and waters analyzed to compare to these historic data. Identifiable trends showing general increases in ion concentration over time were found in the river locations with long-term historical data sets. The time series at some localities were not complete due to many gaps in data collection over the past 40-50 years. Historical averages for chloride showed increased concentration downstream at sites along the Olentangy River, possibly reflecting increased road salt application near more urban areas of the watershed. Sodium concentrations in 2012-2013 central Ohio samples were all lower than respective Cl^- concentrations, possibly reflecting the participation of Na⁺ in ion exchange reactions or the presence of CaCl₂ as an impurity in road salt relative to NaCl. High chloride to bromide mass ratios in the Ohio surface waters revealed that the source of chloride was likely halite, or road salt. Analysis of ³⁶Cl/Cl in 2012 Olentangy River and Darby Creek samples reveal very low values compared to the expected background ratio, suggesting the addition of “old” chloride into the water system, possibly from halite used as road salt. Observations of some of the Ohio rivers are similar to what have been observed elsewhere in the U.S., but others show no real trends. A lack of consistent long-term data leads to a lack of certainty in interpretation at some locations.