Publication Date
4-8-2008
Abstract
Kampoosa Bog is the largest and most ecologically diverse calcareous lake-basin fen in Massachusetts. Situated within a 4.7 km2 drainage basin, the open fen consists of a floating sedge mat that overlies peat and lake clay deposits. Mineral weathering of marble bedrock supplies highly alkaline ground and surface waters to the fen basin. The natural chemistry has been greatly altered by road salt runoff from the Massachusetts Turnpike. The purpose of this study is to characterize the hydrologic and chemical response of the wetland during snowmelt events to understand the fate and movement of road salt (NaCl). Concentrations of Na and Cl in the fen groundwater are greatest close to the Turnpike. Concentrations decrease with distance downstream but are still greatly elevated. During snowmelt events, the fen's outlet shows a sharp rise in Na and Cl concentrations at the onset of melting that is soon diluted by the added meltwater. The Na and Cl flux, however, is greatest at peak discharge, suggesting that high-flow events are significant periods of export of dissolved salts from the fen. Pure dissolution of rock salt produces an equal molar ratio between Na and Cl, and sodium and chloride imbalances in stream and ground waters suggest that ~20% of the Na is stored on cation exchange sites within the peat. The largest imbalances between Na and Cl occur deeper within the peat, where the peat is more compact and groundwater has a longer residence time. CEC measurements show that Ca>Mg>Na>K on exchange sites and suggest that Na in groundwater preferentially displaces Mg. Management questions to be addressed include what percentage of applied salt is flushed through the fen during snowmelt each year? How much salt is retained in the fen? For how long would salt concentrations remain elevated if salt application were to cease?