DISTRIBUTION OF DEICING SALTS IN SOILS

Examining rates of deicing salt accumulation and leaching in soils is important for understanding the distribution and movement of salt in the environment. We examined variations in concentrations of cations associated with deicing salt in soils on the Vassar College campus, in eastern New York, in September-November. The mixed landscape of a college campus provides a useful contrast to previous studies that have focused on isolated, rural highways. We used atomic emission spectrophotometry to measure concentrations of Na, Mg, Ca, and K in soils at randomly located sample sites as well as in 3-m transects adjacent to sidewalks and parking lots. Among 5 measures of proximity to salted surfaces, distance to nearest salted surface provided the best and simplest explanation of cation distribution. Among all samples, average cation concentrations were as follows: Na 13 mg/100 g soil; Ca, 150 mg/100 g; Mg, 30 mg/100 g; K 8 mg/100 g. All cations declined with distance to pavement on transects and when all observations were analyzed together. Abundant Ca and Mg, and rapid declines in Ca and Mg within 3 m of salted surfaces, were consistent with abundant use of CaCl₂ and MgCl₂ near buildings. Overall moderate levels of Na, including near salted surfaces, suggested that Ca and Mg displaced Na in soils. Sodium concentrations taken from a subset of “clean” off-campus soils averaged 9 mg /100 g soil, which suggests that Na was broadly distributed, either through dust movement from road salt or through long-range aerosol transport and precipitation. Soils provide a significant reservoir for salts year-round, and Mg and Ca may help mobilize Na into groundwater and surface water systems.