Weather-related effects on woodland vernal pool hydrology and hydroperiod

Abstract

Woodland vernal pools occur commonly throughout northeastern North America. These pools provide preferred breeding habitat for mole salamanders (Ambystoma spp.) and wood frogs (Rana sylvatica) and support an abundant and diverse macroinvertebrate fauna. Vernal pool hydrology, and especially hydroperiod or duration of the wet phase, affects the composition and productivity of pool fauna. The hydrology of ephemeral wetlands is dominated by local weather conditions. In this paper, I report a ten-year record of the relationships between precipitation and evapotranspiration and water-level change and hydroperiod in four typical southern New England vernal pools. Long-term average precipitation is evenly distributed throughout the year in the Northeast; potential evapotranspiration peaks in the summer months and exceeds precipitation from mid-June through mid-September. This period of water deficit causes the period of maximum vernal pool drying. Vernal pool hydroperiods were shorter and pools dried earlier in those years with larger cumulative water deficits, especially when early spring ground-water resources were below long-term means and late winter snowpack was reduced or absent. Weekly water-level change in vernal pools was significantly related to precipitation and potential evapotranspiration, with precipitation having 2–5 times greater effect than evapotranspiration. Under elimate-change predictions of more episodic precipitation and increased evapotranspiration, vernal pools would dry earlier in the year and remain dry longer. These changes would adversely affect the successful reproduction of pool-breeding amphibians and isolate the remaining productive pools.