Hydrologic assessment of seasonal pond response to large-volume groundwater withdrawal

Seasonal ponds are small wetland basins that typically hold water in spring and early summer and dry out by late summer. The hydroperiod, the amount of time the ponds hold water, is an important factor in the habitat suitability of these ponds for species that use these ponds as breeding sites. In southern Rhode Island, wood frogs (Lithobates sylvaticus LeConte) and spotted salamanders (Ambystoma maculatum Shaw) require 17 and 24 weeks of inundation, respectively, for 50% juvenile emigration from the pond into the terrestrial habitat. Groundwater withdrawals from large-volume municipal wells can have a negative impact on the hydroperiod of these ponds and so on their habitat suitability. Narcisi (2010) tested the habitat suitability for pond-breeding amphibians of 24 seasonal ponds around two municipal well fields in southern Rhode Island. He determined that the hydroperiods of well field ponds were significantly shorter than those observed at ponds not adjacent to wells. The purpose of this study was to research and characterize the hydrologic controls on seasonal pond hydroperiods and to determine the effects of pumping on the habitat suitability of these ponds. Three methods were utilized to assess the hydrologic inputs and outputs including temperature tracers, piezometers, and water chemistry. Additionally, the non-equilibrium Theis equation was used to model drawdown in the area around each of the ponds. Ten out of thirteen well-field ponds were connected to the groundwater system. Comparison of rates of water loss in 2008 and 2009 between the controls and the well-field ponds revealed that nine ponds were susceptible to impacts from high-volume groundwater withdrawal. The three perched ponds (not connected to the water table) were not impacted by pumping. The one pond connected to the water table but not impacted was too far away from the nearest well. The hydroperiod data indicate that although nine ponds were impacted by pumping in 2009 only five of those ponds were unable to sustain breeding populations of wood frogs and spotted salamanders. This study proposes that a program utilizing techniques described in this study be implemented into Rhode Island's high-volume well permit process to provide protection for these ponds in the future.