Influence of Soil Physicochemical Properties on Hydrology in Carolina Bay Wetlands

Carolina bays are shallow depression wetlands found in the southeast US that have been severely altered by human activity. In addition, for relatively unaltered bays a predictive model to assess hydrologic impacts ITom land use changes and industrial activities in required. Our understanding of basic wetland hydrological processes is limited, and subsequently, our ability to predict andlor assess the. effectiveness of bay restorations or land use effects is hindered. Hiegersell et al. (2003) conducted an analysis of the bay hydroperiod length in relation to the predicted depth to groundwater at the Savannah River Site using an 8-year period of record on over fifty bays monitored by the Savannah River Ecology Lab. The results demonstrated that the average hydroperiod was significantly longer as the depth to groundwater decreased (see attachment). However, within group variation was large. In other words, some bays within a few feet of groundwater had shorter hydroperiods than bays in which the depth to groundwater was> 8 meters. Differing physicochemical properties of soils within bay interiors may also control bay hydrology. However, previous efforts to establish relationships between soil characteristics and bay hydrology have been inconclusive and the question remains as to why some bays are ponded throughout the year while others, within a similar landscape unit, are predominantly dry. An assessment of soil and hydrologic characteristics was initiated in 6 undisturbed bays to determine if a relationship exists. Soil morphology was described and permanent monitoring wells were installed at each site. Soil samples were collected by horizon to a depth of 2 meters at the topographic center of each site, then analyzed. After three years, multiple regression analysis (stepwise backward and forward) was used to establish relationships between the soil physicochemical characteristics and bay hydroperiod in the undisturbed sites. A significant relationship (r2 =0.96) between hydroperiod and clay content in the argillic horizon (8t) was observed in the undisturbed sites (Figure I). Although encouraging, the small sample size (n=6) does not provide the statistical power desired to make a firm affirmation that clays are controlling hydrology in these sites. As such, addition effort to evaluate this relationship at other bays with long-term hydrologic data is proposed to further refine the model.