HYDROGEOLOGICAL ANALYSIS OF FACTORS THAT INFLUENCE PITCHER PLANT BOG VIABILITY AT THE JOSEPH PINE PRESERVE, SUSSEX, VIRGINIA

The purpose of this research is to analyze a hydrogeologic setting that supports native pitcher plant bogs in the coastal plain of Virginia, and evaluate the effects that watershed-wide alterations to the vegetation have on groundwater dynamics. Longleaf pine savanna and pitcher plant bog ecosystem complexes were once common in Virginia’s coastal plain, but fire suppression and other factors contributed to a significant decline in these wetlands. Re-creation and maintenance of these savannas requires considerable effort and expense. A comprehensive understanding of these ecosystems, such as the ones at the Joseph Pine Preserve, needs an evaluation of the interaction between the abiotic and biotic elements that formed it.

The tidal-flat facies of the Bacons Castle Formation underlie the rolling landscape of the Preserve. Analysis of auger and vibracore samples revealed bogs in that setting formed at toeslopes where groundwater seeps from extensive sand layers that are laminated between thick clay beds. Hydrographs from monitoring wells in those sand beds reveal relative stable water table elevations above the bog root zone even throughout the intense summer drought conditions in 2010. Diurnal fluctuations in the groundwater table reflected evapotranspiration cycles. Comparisons of evapotranspiration rates between adjacent areas with different vegetation densities indicate a notable difference in the volume of groundwater withdrawn by dense mixed pine/deciduous hardwood forest and sparsely-wooded longleaf pine savanna. This result suggests longleaf pine savanna ecosystems withdraw less groundwater, effectively increasing the volume of water available to supply the pitcher plant bog. This study will provide resource managers with information critical for restoring these rare wetland habitats.