Alteration of water levels in a Massachusetts coastal plain pond subject to municipal ground-water withdrawals

The coastal plain ponds that occur within glacial deposits in the northeastern U.S. experience annual and inter-annual water level fluctuations. Periodic inundation and drying of coastal plain pond shorelines has led to the development of pondshore vegetation communities that are unusually diverse and restricted in distribution. Because water level fluctuations are the primary abiotic control on plant community composition and dynamics, ground-water extraction for municipal supply has the potential to alter pond hydroperiod and plant community structure. We assessed the influence of ground-water pumping on pond levels at Mary Dunn Pond in the Hyannis Ponds Complex in Barnstable, Massachusetts. Short-term well pumping tests, seepage rate measurements, and measurements of surface-water and ground-water temperatures during pumping tests provided unequivocal evidence of an intimate surface-water/ground-water connection. A regression model that related pond levels to pumping and natural background variations in water levels from 1976-2003 indicated that pumping affected water levels in all seasons and that the drawdown from high intensity pumping during 1983-91 persisted for more than one year. The model also indicated that pumping truncated ecologically significant multi-year periods of high water. Pumping shifted the zone of pond-level fluctuations to lower elevations of the Mary Dunn Pond shore and into more organic-rich soils potentially diminishing plant community diversity over the long term. The current rates of pumping, instituted in 1992 after a severe drawdown, more closely approximated the natural hydrologic regime. Planning agencies and water suppliers should consider the ecological effects of ground-water withdrawals in water supply planning and during management of existing wellfields in similar hydrogeologic settings.