Belowground Productivity and Nutrient Cycling Across a Salinity Gradient In Tidal Freshwater Forested Wetlands of South Carolina.

Tidal forests are unique and productive ecosystems in the southeastern United States, and are highly susceptible to ecological changes. Many of these wetlands are vulnerable to rising sea level and developmental impacts; however they have not been researched to the extent of other wetlands. Consequently, considerable ambiguity exists in regards to the relationships between vegetation production and carbon, nitrogen, and phosphorus flux. We are studying belowground net primary productivity (BNPP) and nutrient limitations across three sites along a salinity gradient on the Waccamaw River in South Carolina. Primary objectives of this study include quantifying BNPP, determining nutrient limitations, and assessing other biogeochemical indices along the gradient. The sites were significantly different in terms of pH and ranked as follows: least saline (4.8), intermediate (5.2), and most saline (5.5). The intermediate site was significantly different than both the other sites in extractable soil phosphorus (17.6 mg/kg verses an average of 11.1 mg/kg on the other sites). However, the least saline site was significantly higher in soil carbon (230000 mg/kg) and nitrogen (14300 mg/kg) concentrations compared to other sites. Preliminary data from the last quarter of 2010 show biomass of live roots at the intermediate site being greater than the other sites in September (1000 g·m²) and October (1076 g·m²). The intermediate site also had the greatest amount of dead root biomass during this time, with 803 g·m² in September and 907 g·m² in October. However, the most saline site exhibited the greatest mass of dead and live roots (666 g·m² and 161 g·m², respectively) in December which suggests a strong seasonal influence. Results from this study will enhance our understanding of the role of these wetlands in global net primary productivity, nutrient cycling, and carbon dynamics.