STORAGE AND RELEASE OF ROAD-SALT CONTAMINATION FROM A CALCAREOUS LAKE-BASIN FEN, STOCKBRIDGE, MASSACHUSETTS, USA
Detailed sampling of surface and ground waters during three snowmelt events illustrate early releases of Na and Cl from shallow groundwater at the onset of melting, with maximum fluxes of ions coinciding with peak discharge. The flux of dissolved salts exiting the wetland during one snowmelt event accounts for 13% (Na) and 17% (Cl) of rock salt applied to the highway during that year. The mass of exported Na and Cl is proportional to the number of lane miles crossing the watershed. During 2005, the annual flux estimates of Na and Cl are on par with the amount of road salt applied, with more than half of the annual flux occurring during the months of March, April and May. Subsequent large rain events disrupted prior apparent equilibrium conditions, causing Na to desorb from cation exchange surfaces and increase net export of Na and Cl from the fen. Large rain events outside of winter months are more effective than snowmelt with reduction of dissolved salts because snowmelt also introduces contamination. For this and other wetlands having alkaline geochemistry and high flushing rates, management strategies that reduce rock salt amounts to roadways will assist with reducing contamination to levels that may be less toxic to vegetation and aquatic organisms.