Calibration of modern pollen along a nutrient gradient in Everglades WaterConservation Area-2A

In the past 100 years, the hydrology and nutrient levels of the Florida Eve rglades, USA, have been drastically altered by a system of canals and dikes and urban and agricultural development. Levels of soil total phosphorus (T P) have become elevated in the northern part of Water Conservation Area 2A (WCA-2A). Vegetation community changes in the past 20 years in this impacte d area are characterized by the invasion of Typha domingensis into historic ally Cladium jamaicense marshes and aquatic slough communities. The objecti ve of this study was to calibrate modern pollen assemblage data from surfac e soil samples with soil nutrient data and observed macrophyte changes acro ss a TP gradient at 31 sites in WCA-2A. Soil TP, nitrogen, carbon, biogenic silica, and calcium analyses of soils were included in the study. Modern p ollen distribution corresponds to living macrophyte community variation alo ng a TP gradient in WCA-2A. Pollen assemblages associated with three major marsh types in WCA-2A (Typha-dominated, Cladium-dominated, mixed Typha-Clad ium) can be defined. Multivariate statistics show that the parameters measu red explain about half of the variance in pollen data. TP was the only para meter measured that explains a significant amount of the variation. The rem aining chemical variables tested were not significant. Clearly, other envir onmental factors not measured for this study also affect distributions. Alt hough not analyzed statistically, hydrology patterns in WCA-2A. probably pl ay an important role based on pollen cluster analysis. A weighted averaging (WA) regression model for TP from the pollen assemblages has a high correl ation coefficient (r(2) = 0.76) between observed and inferred values. This model can be used to estimate present plant community structure based on so il TP content in WCA-2A (e.g., optimal TP levels for specific taxa) and pas t TP levels based on pollen assemblages found in dated soil core subsamples . Moreover, historical plant community assemblages can be reconstructed fro m pollen profiles. Such reconstructions are essential to the restoration of the Everglades.