MARSH VEGETATION PATTERNS AND SOIL-PHOSPHORUS GRADIENTS IN THE EVERGLADES ECOSYSTEM

In order to test the hypothesis that phosphorous enrichment is modifyi ng Everglades marsh community composition, we sampled vegetation and s oil phosphorus concentrations along four transects in areas representa tive of varying environmental conditions within the Everglades region. Each transect originated at or near a canal flow control structure an d extended towards the center of the marsh because the canal flow stru ctures were seen as potential nutrient input sources from 'upstream' a gricultural areas. Cladium jamaicense, wet prairie communities and Typ ha spp. dominated sites were sampled along each transect. Correlations for between-species occurrences and between-species frequencies and p hosphorus concentrations with distance from nutrient source were deter mined. Within-transect effects and between-transect effects from north to south across the Everglades region were compared. In all cases pho sphorus concentrations and presence of Typha domingensis showed a nega tive relationship to distance from nutrient source, while the presence of Cladium and other natural communities showed a positive one. The p attern in marsh community composition and soil phosphorus content seen in the four marsh transects indicates that a strong relationship exis ts between Typha expansion, decline of Cladium marsh and wet prairie c ommunities and rising phosphorus concentrations, and that these trends are correlated with nutrient input sources associated with agricultur al runoff.