Calibration of modern pollen along a nutrient gradient in everglades water conservation area-2A

In the past 100 years, the hydrology and nutrient levels of the Florida Everglades, USA, have been drastically altered by a system of canals and dikes and urban and agricultural development. Levels of soil total phosphorus (TP) have become elevated in the northern part of Water Conservation Area 2A (WCA-2A). Vegetation community changes in the past 20 years in this impacted area are characterized by the invasion of Typha domingensis into historically Cladium jamaicense marshes and aquatic slough communities. The objective of this study was to calibrate modern pollen assemblage data from surface soil samples with soil nutrient data and observed macrophyte changes across 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 pollen distribution corresponds to living macrophyte community variation along a TP gradient in WCA-2A. Pollen assemblages associated with three major marsh types in WCA-2A (Typha-dominated, Cladium-dominated, mixed Typha-Cladium) can be defined. Multivariate statistics show that the parameters measured explain about half of the variance in pollen data. TP was the only parameter measured that explains a significant amount of the variation. The remaining chemical variables tested were not significant. Clearly, other environmental factors not measured for this study also affect distributions. Although not analyzed statistically, hydrology patterns in WCA-2A probably play an important role based on pollen cluster analysis. A weighted averaging (WA) regression model for TP from the pollen assemblages has a high correlation coefficient (r2 = 0.76) between observed and inferred values. This model can be used to estimate present plant community structure based on soil TP content in WCA-2A (e.g., optimal TP levels for specific taxa) and past TP levels based on pollen assemblages found in dated soil core subsamples. Moreover, historical plant community assemblages can be reconstructed from pollen profiles. Such reconstructions are essential to the restoration of the Everglades.

Duke Scholars

Author Curtis J. Richardson Environmental Sciences and Policy