ANALYSIS OF GEOLOGIC SETTINGS AND HYDROLOGIC CONDITIONS THAT AFFECT RESTORED PITCHER PLANT BOG HABITAT, SUSSEX COUNTY, 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. Because re-creation and maintenance of these savannas, such as the ones at the Joseph Pine Preserve in Sussex County, Virginia, require considerable effort and expense, effective management plans must be based upon a comprehensive understanding of the interaction between the geologic, hydrologic, and biotic elements that formed them.

The tidal-flat facies of the Bacons Castle Formation underlie the rolling landscape of the Preserve. Analysis of split-spoon cores, and vibracore samples revealed bogs in that setting formed at toeslopes where groundwater seeps from extensive sand layers sandwiched between thick clay beds. Examination of bog stratigraphy across the toeslope using ground-penetrating radar reveals colluvial sand sheets overlie dense clay layers. Hydrographs from monitoring wells in those sand beds show relative stable water table elevations above the bog root zone existed even during summer drought conditions in 2010. Diurnal water table fluctuations reflected evapotranspiration cycles. Comparisons of ET rates between adjacent areas with different vegetation densities indicate a 103% increase in the volume of groundwater withdrawn by dense mixed pine/deciduous hardwood forest compared to sparsely-wooded longleaf pine savanna. Also, analysis of groundwater fluctuations before and after prescribed burning of the long-leaf savanna ecosystem in spring 2011 show a reduction in post-burn evapotranspiration rates. These results suggest long-leaf pine savanna ecosystems managed with annual prescribed burning withdraw less groundwater than loblolly pine woodlands, 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.