Phosphorus biogeochemistry in the secondary succession of former rice impoundments on the upper Cooper River, South Carolina.

摘要

Differences in the biogeochemistry of phosphorus among wetland habitats in different stages of succession along the Cooper River (CR), South Carolina were studied with an emphasis on increasing our understanding of the water quality functions of tidal wetlands. Primary production increases during the transition of the former rice fields from open water to intertidal emergent vegetation. Consequently, demand for inorganic P by primary producers increases while dominance of the sediment phosphorus pool by organic P increases from 69% to 95% and the amount of inorganic P decreases. Consequently, excretion of phosphatase enzymes by plants and microbes plays an important role in the succession process. In our study, acid phosphatase, alkaline phosphatase and phosphodiesterase activities in the marsh sediments were found to increase along the successional gradient. Acid phosphatase was the dominant enzyme in all stages of succession.; Factors that regulate primary production vary in importance from one successional stage to the next within the former rice fields, and the ecological values of a wetland, such as its water quality function, will depend on the factors that control primary production. For example, a wetland that is phosphorus limited is most likely act as a stronger sink for phosphorus than a wetland that is limited by nitrogen or other factors. Regulation by water depth and inundation frequency (duration) is probably important in all stages of succession. In the habitats at the early or intermediate successional stages, hydrological conditions controlled the introduction and/or establishment of highly productive emergent species while N or P were apparently not a limitation. In the early or intermediate successional stages, marsh sediments exchange phosphorus with the overlaying water column, adsorbing or releasing phosphorus depending on the diffusion gradient between the sediment and surface water. In the late successional stage, P cycling is more closed, and biotic P demands are satisfied through P mineralization, or internal loading, and nitrogen was the primary limiting nutrient.