FATE AND TRANSPORT OF ROAD SALT CONTAMINATION THROUGH A CALCAREOUS FEN: KAMPOOSA BOG, STOCKBRIDGE, MA

Kampoosa Bog is the largest and most ecologically diverse lake-basin fen remaining in Massachusetts, and it is one of Massachusetts' elite Areas of Critical Environmental Concern (ACEC). The groundwater chemistry of the fen has been greatly altered by road salt runoff (NaCl) from the Massachusetts Turnpike. Ground water samples collected at different depths within the fen, measurements of exchangeable Na on peat, and hydraulic conductivity measurements in peat suggest that flow of contaminated ground water is largely a near-surface phenomenon.

Detailed sampling of surface and ground waters during three spring snow melt events and one precipitation event shows rapid export of dissolved salt from the wetland during hydrologic events. The flux of dissolved salts leaving the wetland is most strongly controlled by discharge of the outlet stream, with greatest flux occurring at peak discharge. The total flux of dissolved salts (39 tons Na and 78 tons Cl) during a 30-day snowmelt period in 2005 account for 14% (Na) and 18% (Cl) of the annual application of rock salt to the Massachusetts Turnpike within the Bog's drainage area. The months of March, April and May are the primary months for salt export, accounting for more than half of the annual salt flux. Na:Cl ratios for surface and ground water samples are less than one, and sodium and chloride imbalances suggest that 20-30% of Na from rock salt is stored on cation exchange sites on organic material. Na appears to preferentially exchange with Mg, and high concentrations of calcium in ground water and on cation exchange sites may inhibit significant exchange between Na and Ca. Na:Cl ratios greater than one are observed in fen groundwater under more dilute conditions, suggesting that sodium can be released from cation exchange sites back to ground water. Concentrations of Na and Cl in shallow ground water of the fen have decreased from 2002 through 2007. The mass of Na and Cl exported from Kampoosa Bog is consistent with the length of road-lane miles crossing the watershed, and the steady decline in Na and Cl concentrations may reflect lower amounts of salt applied to the Turnpike because of fewer storms in recent winters. These results suggest that the geochemistry of Kampoosa Bog will respond to management strategies that target the deicing agents applied to the highway.