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This study presents an application of a three‐dimensional kriging technique to estimate spatial distribution of total mercury (Hg) in the Cedar‐Ortega Rivers watershed located in the lower St. Johns River basin, Florida. The kriging procedures, including preliminary data analysis, structural data analysis and the log kriging estimation, are presented. Results show watershed wide Hg contamination of river sediment to a depth of 1.0 m. A three‐dimensional plot of Hg against the Florida Sediment Assessment Guidelines (i.e., the probable effect level or PEL) demonstrates that the Cedar River is more contaminated with Hg than the rest of the watershed. The maximum sediment depth with Hg concentrations above PEL value (0.696 mg/kg) is 1.5 m. Hg concentrations at or above this level could pose a significant hazard to aquatic organisms. Analysis of the spatial distribution of Hg in the watershed finds multiple input sources. This study suggests that there is a need to identify the major sources of Hg in the watershed, and to determine the pathways that allow Hg to enter the river.

Twenty-four fresh marsh-wet prairie wetland sites in southwestern Florida were studied with respect to vegetation zonation, substrate characteristics, and morphometry.Six major wetland zones were identified.The Hypericum zone occupied the shallowest position (closest to the upland edge) and was confined to ~andy substrates.The Panicum-Rhynchospora zone typically followed downslope and was also associated with sandy substrates.The Mixed Emergent, CLadium, Cephalanthus and Fraxinus-Salix zones all occurred on organic soils in wetland interiors.In addition to depth and substrate type, other important determinants of zone composition included fire and disturbance due to feral hog rooting and cattle grazing.