Effects of phosphorus enrichment on structure and function of sawgrass and cattail communities in the Everglades

Anthropogenic phosphorus (P) loading has resulted in increased soil P concentrations over a significant portion of the northern Everglades. Changes in macrophyte community structure and function associated with soil P enrichment are examined by reviewing recent field and laboratory studies in the Everglades conducted by the South Florida Water Management District and University of Florida. Of primary interest is the widespread replacement of the native sawgrass marsh by cattails in Water Conservation Area 2A (WCA-2A). The spatial distribution of cattails (Typha domingensis) in WCA-2A correlates strongly with soil P concentration. Comparative studies in P-enriched and reference areas of WCA-2A demonstrated increased macrophyte production and photosynthesis in the P-enriched area. Field P gradient studies indicate that macrophyte communities in the reference area of WCA-2A are P limited. Plant tissue nutrient concentration, storage, and distribution in macrophyte communities changed significantly along the P gradient. In addition, the rate of detrital organic carbon turnover increased with P enrichment. Sawgrass (Cladium jamaicense Crantz) and cattail exhibit contrasting resource allocation patterns that are characteristic of plants adapted to low- and high-nutrient environments, respectively. Soil P enhanced cattail rhizome expansion and leaf growth after disturbances. The results suggest that a shift from a P-limited to a P- enriched system in WCA-2A has contributed significantly to the recent spread and dominance of cattail, a previously restricted native species, in P-enriched areas of the marsh.