Ecohydrology of a Floodplain Forest: Relationships Between Vegetation and Groundwater Response at Congaree National Park, South Carolina, USA
Senn, Lauren Hernandez-Rubio
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Congaree National Park (CONG) supports high biodiversity and provides ecosystem services for the surrounding area in the floodplain wetland system, especially in bottomland hardwood forests which contain some of the last remaining old-growth stands in the eastern U.S. Maintaining ecosystem functions is essential not only for the conservation of biodiversity, but also for the ecosystem services provided, such as nitrification, denitrification, decomposition, and carbon sequestration. Because management practices of the park depend on understanding the area's hydrology, past research has been performed to analyze the flooding of Congaree River. However, not much has been done to better understand groundwater movement through the floodplain sediments in the Congaree River Valley. The goal of this project was to quantify interactions between the shallow unconfined aquifer and local vegetation around eight sites of the Congaree Observation Well Network at CONG. This was done by estimating evapotranspiration rates, specific yield of sediments, vegetation diversity, and basal area. Data were collected on groundwater response to storm events, and diurnal signals caused by evaporation and transpiration in the forest. Vegetation community structure and local topography were also studied. These variables were analyzed to better understand their effect on vegetation water demand in this wetland system. Methods included calculating estimated evapotranspiration for summer months from 2009-2012, as well as a vegetation survey of 400 m<sup>2</sup> plots at the eight sites. Basal area index was calculated from diameter at breast height measurements of all woody stems within each plot. It was found that evapotranspiration and basal area were not correlated across the sites, suggesting that local topography changes in the form of hummocks and hollows may influence groundwater flow at these sites. Vegetation composition was found to be typical of floodplain forest associations previously described for CONG. The results of this study provide baseline data for future research, along with information that could help develop management guides for flood control and predictions for forested wetland sites.