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ABSTRACT
During the past century, the historical hydrology and nutrient regimes of the Everglades, a 700,000 hectare freshwater wetland in southern Florida, have been altered by agricultural and urban development. Changes in plant community composition (e.g. encroachment of cattail (Typha domingensis Pers.) into sawgrass (Cladium jamaicense Crsntz) and slough communities) have been observed in areas receiving nutrient and water loadings from agricultural activities. The distribution of 210Pb and pollen in depth increments of peat was measured at a nutrient-enriched site and an unenriched site in Water Conservation Area 2A (WCA 2A) to describe how nutrient enrichment and water management might have altered the historical plant species composition of the Everglades. Species composition of the plant communities has changed during the past 20 to 50 years at both enriched and unenriched sites. At the unenriched location, there has been a general shift in community composition since 1950 as slough species (arrowhead (Sagittaria spp.), water lily (Nymphaea spp.)) have decreased and terrestrial plants (pigweed (Amaranthaceae), ragweed (Ambrosia spp.), and Eupatorium spp.) have increased. The nutrient-enriched site also has seen an increase in terrestrial plant species since about 1950. In addition, since 1970, the sawgrass and slough communities at the enriched site have been replaced by a cattail-dominated community. The increase in terrestrial vegetation at both sites since 1950 could be due to drainage activities (construction of canals and levees) along the eastern perimeter of the Everglades and in the Everglades Agricultural Area (EAA) during the 1950s. The increase in cattail and concurrent decline in slough species at the nutrient-enriched site since 1970 probably is the result of the massive inputs of water (459,000,000 m3yr−1) and nutrients (1814 MT Nyr−1, 60 MT Pyr−1) from the EAA since WCA 2A was impounded in 1961.