The Effects of Road Salt on Stream Water Chemistry in Two Small Forested Watersheds, Catoctin Mountain, Maryland, USA

摘要

The Hauver Branch and Hunting Creek watersheds in Catoctin Mountain, Maryland, USA, are small rural watersheds that receive road salt during the winter. Base cation evidence of road salt application in stream water disappears by approximately September for Hauver Branch, but never disappears for Hunting Creek. The fraction of the precipitation-corrected watershed fluxes of both Mg~(2+) and Ca~(2+) attributable to cation exchange associated with road salt Na~+ inputs are 14 and 19 % for Hauver Branch and Hunting Creek, respectively. The percentage of divalent cations in stream waters resulting from road salt application is calculated using the watershed chemical weathering Na~+/SiO_2 molar ratio. Calculation of a representative chemical weathering Na~+/SiO_2 molar ratio may be problematic with spatially variable bedrock, and/or inputs from water softeners, septic systems, and wastewater treatment plants. Therefore, investigations of small forested rural watersheds offer insights into road salt dynamics that may be lost at larger scales and/or with increased urbanization. The quantities of road salt application to the Hauver Branch and Hunting Creek watersheds are 3.3 and 11 t km~(-2) year~(-1), respectively. The per-lanelength- normalized road salt application rates for the Hauver Branch and Hunting Creek watersheds are 10 and 22 t lane~(-1) km~(-1) year~(-1), respectively. These per-lane-length-normalized road salt application rates are relatively large compared to more urbanized watersheds located north of the study site where the application rates are reported by municipalities. These findings may indicate that road and highway administrations may underestimate their rates of road salt application.