FRESHWATER MARSH COMMUNITY STRUCTURE IN A FLORIDA EVERGLADES MESOCOSM

Considerable research activity has been undertaken to characterize the effects of nutrient cycle changes on the distribution of plant communities in the Florida Everglades. Studies of constructed Everglades ecosystems at the mesocosm scale offer avenues for researching the complexities of these interactions. The objectives of this study were to describe the vegetation that developed in the Florida Everglades mesocosm in Washington, D.C., a greenhouse-sized constructed Everglades ecosystem in operation from 1987 to 2001. Literature on actual Everglades vegetation was used to make comparisons with the vegetation in the mesocosm. The entire standing herbaceous biomass was harvested from the mesocosm's cattail and sawgrass communities, and samples of belowground biomass were taken from various points throughout. Dry weights of the samples revealed the highest overall aboveground biomass (2223 g m(-2)) in the mixed cattail/sawgrass community of the emergent marsh/herbaceous hummock section, and the lowest (1302 g m(-2)) in the grass prairie. The highest belowground biomass (4058 g m(-2)) was also found in the marsh/hummock, and the lowest (64 g m(-2)) was found in the marsh/pond. These biomass values fall within the ranges found in the literature on productivity of cattail and sawgrass communities. The distribution of the plant species fluctuated between the community sections, with species richness highest in the grass prairie and lowest in the marsh/pond. The fluctuations of plant assemblages between the community sections give evidence that the sections may represent the transition zone between tree islands and sawgrass marsh communities found in the wild. Soil and leaf nutrient contents were within expected ranges of their natural analogs, although no significant differences were seen between the cattail and sawgrass populations. Artifacts of the mesocosm were strongly evident, such as edge effects in community density, yet the ecological structure of the mesocosm was strikingly close to that found in the wild Everglades. Overall, the experience with the management, harvest, and study of the Florida Everglades mesocosm demonstrates the value of large-scale mesocosm studies for representation of ecological structures and functions.