Recent and abrupt environmental change in the Florida everglades indicatedfrom siliceous microfossils

We used paleoecological methods to infer environmental conditions in Water Conservation Area 2A (WCA-2A) of the Everglades before impoundment in 1961, and we compared pre-impoundment environmental conditions to present condit ions. Abundances of siliceous microfossils (diatoms, chrysophyte cysts, spo nge gemmoscleres, and plant phytoliths) were analyzed in two sediment cores from nutrient-enriched northern WCA-2A and in two sediment cores from unen riched southern WCA-2A. Nutrient enrichment in northern WCA-2A after 1961 w as associated with an increase in relative abundance of eutrophic diatoms. A pH increase in much of WCA-2A after 1961 was indicated by a decrease in r elative abundance of acidic indicators (Eunotia diatoms and the sponge Anhe teromeyenia ryderi) and a decrease in richness of chrysophyte cysts. An inc rease in anoxia in nutrient-enriched northern WCA-2A, during about 1961-198 0 when high water depth was maintained, was suggested by an increase in vis ible dissolution of siliceous microfossils. A decrease in palm phytolith ab undance after 1961 and lack of recovery after water depth was lowered sugge st either that water depth is still maintained high enough to adversely aff ect vegetation or that there has been insufficient time for recovery. Numbe rs of sponge gemmoscleres decreased to less than 1% of preimpoundment numbe rs, suggesting that there has been a dramatic decrease in sponge abundance. The environmental changes discovered in this study suggest directions for future management of the Everglades.