Interactions of Hydrology, Soils, and Plants in Natural and Restored Carolina Bay Wetlands.

Carolina Bays are oval-shaped depressional wetlands in the Atlantic Coastal Plain that are all oriented in a NW to SE direction.  Most of the 500,000 bays probably formed as shallow lakes that evolved into wetlands. Many of the bays have been drained for agriculture and are prime candidates for wetland restoration.  Successful restoration requires that both the hydrology and vegetation be restored to maximize mitigation credits.  Research on natural, drained and restored Carolina Bays was conducted over a 14-yr period. Records of water table levels were extended to 40 years using hydrologic modeling.  Water table depths in natural bays were <0.1 m most of the year and groundwater inflow was a significant component of the water balance near the perimeters of the bays. Wetland plant communities in natural Carolina Bays were influenced by long-term soil saturation and flooding regimes as well as organic layer thickness and P levels.  Draining and farming a bay wetland lowered the water table and allowed oxidation of organic soil layers to occur.    Surfaces of organic soils subsided 2 cm yr^-1 following drainage.  Water levels relative to present surface elevations in restored wetlands must be managed to minimize ponding in subsided areas to avoid killing restored vegetation.  Growers also added N, P, and lime annually which altered soil properties to depths exceeding 1 m.  The P that accumulated in farmed soils can be solubilized under reducing conditions following wetland restoration.  In isolated wetlands with minimal hydraulic gradients, little P will leave the site because groundwater is virtually stagnant.  Vegetation can take up some of the soluble P, but amounts will be small and on the order of 26 kg P ha^-1.  In summary, Carolina Bays are ideal candidates for wetland restoration but their unique attributes must be taken into account to successfully restore hydrology and vegetation.