Marsh vegetation patterns and soil phosphorus gradients in the Everglades ecosystem

In order to test the hypothesis that phosphorous enrichment is modifying Everglades marsh community composition, we sampled vegetation and soil phosphorus concentrations along four transects in areas representative of varying environmental conditions within the Everglades region. Each transect originated at or near a canal flow control structure and extended towards the center of the marsh because the canal flow structures were seen as potential nutrient input sources from 'upstream' agricultural areas. Cladium jamaicense, wet prairie communities and Typha spp. dominated sites were sampled along each transect. Correlations for between-species occurrences and between-species frequencies and phosphorus concentrations with distance from nutrient source were determined. Within-transect effects and between-transect effects from north to south across the Everglades region were compared. In all cases phosphorus concentrations and presence of Typha domingensis showed a negative relationship to distance from nutrient source, while the presence of Cladium and other natural communities showed a positive one. The pattern in marsh community composition and soil phosphorus content seen in the four marsh transects indicates that a strong relationship exists between Typha expansion, decline of Cladium marsh and wet prairie communities and rising phosphorus concentrations, and that these trends are correlated with nutrient input sources associated with agricultural runoff.