HYDROLOGY AND NUTRIENT GRADIENTS IN NORTH-CAROLINA PEATLANDS

Soil chemistry and hydrology gradients are closely associated with and have often been cited as the causative agents for changes in wetland plant community composition. We analyzed the biogeochemistry and hydrology of three freshwater peatland communities on the North Carolina Coastal Plain-short pocosins, tall pocosins, and gum swamps. We compare this community gradient to the classical bog-fen gradient of northern peatlands. Short pocosins, in the ombrotrophic center of the raised bog complex, have the highest summer water table, with a large part of the peat profile remaining anaerobic throughout the year. They are highly nutrient-deficient with low levels of total and extractable P, N, and basic cations. They additionally have the greatest peat depth, with an organic matter content of ca. 95%. Tall pocosins have a highly seasonal water table, shallower peat depth, low soil nutrient levels, and an average soil organic matter content from 76 to 93% in the top 30 cm. Gum swamp forests have a highly seasonal water table and the shallowest peat depth. They are the most minerotrophic community, based on low organic matter and high N and P content of the soil, but have low levels of exchangeable Ca and Mg and low percent base saturation. All communities had low soil pH (< 4). Short pocosins and tall pocosins were effectively differentiated by seasonal hydrology and peat depth but not by soil characteristics, while the pocosins and swamp forest had large differences in seasonal hydrology, peat depth, percent organic matter, and soil nutrients. This community gradient contrasts sharply with the bog-fen gradient of northern peatlands, in which there is an increase in soil pH, basic cations, percent base saturation, and ash content, and a decrease in extractable N, P, and K. This biogeographical comparison suggests a need for further study of the nutrients likely to control plant growth in peatlands (i.e., P, N, and K), in addition to the historical emphasis on basic cations and pH.