Water quality, aboveground productivity, and nutrient dynamics during low flow periods in tidal floodplain forests of South Carolina

Water quality, aboveground productivity (ANPP), and nutrient dynamics were studied in a tidal, freshwater river system in the vicinity of Bull Island located in the coastal plain of South Carolina. The Pee Dee River flows along the northern and western sides while Big Bull and Little Bull Creeks flow along the eastern and southern sides of the island. Results indicated that all water quality parameters measured were lower than standards set by USEPA and USGS, except for phosphorus and sodium concentrations, suggesting no major water quality problems in the river systems. Analyses also revealed that concentrations of most parameters measured, specifically nitrate and total nitrogen, are reduced as the Pee Dee River waters pass through the island toward Bull Creek probably due to plant uptake and denitrification processes. Overall, litterfall, stemwood, and ANPP values found in this study are at the lower end of those reported in other studies of forested wetlands in the southeastern US. ANPP of the island's floodplain forests ranged between 477 g/m2 and 1117 g/m2 among all twelve plots while mean ANPP was 743 g/m2 when all data were combined. The floodplain forests along the Pee Dee River had higher values in all aspects of ANPP than forests along Bull Creek. Analyses revealed that water tupelo leaves placed at the BC site decomposed faster (k = 2.0389) than at the PD site (k = 1.5892). Microenvironmental factors such as temperature and moisture availability were believed to be the major factors influencing decomposition on Bull Island. Ratios of C:N, C:P, and N:P indicated that there is both N and P limitation in the decomposing litter with N being relatively more limited. During decomposition, the percent of C remaining decreased steadily, while P and N remaining showed relatively more fluctuation on both sites. Moisture was a relatively more important factor than either litter quality or temperature in respect to nutrient dynamics during the decomposition. Local hydrological (flow) characteristics occurring on and around the island are believed to be the major factors influencing all ecosystem processes from water quality to productivity and from nutrient dynamics to decomposition.