Concern for elevated levels of mercury in biota as well as nutrient enrichment in south Florida aquatic ecosystems has provided an impetus for studies of the geochemical processes influencing the distribution and cycling of mercury and other environmentally important elements. Knowledge of element variation patterns with depth in sediment, pore water chemistry, and sawgrass chemistry is essential for a comprehensive understanding of these processes. Preliminary results from peat-dominated sediment samples and sawgrass (Cladium jamaicensis) samples show that metabolic elements (for example, K, P, Cu, Fe and Zn) are concentrated in living tissue relative to the sediment whereas non-essential metals (for example, Cr, Co, Pb and Hg) are concentrated mainly in the sediment relative to the sawgrass. Accumulation rates for metals in sediment show a general decrease with depth in the peat cores. For a suite of cores accumulation rates for different elements appear to vary along a 45 mi northeast-southwest transect beginning in Water Conservation Area (WCA)-2A and progressing into Everglades National Park (ENP). For example, accumulation rates for Ni, V, and Zn show only subtle differences between sampling sites, whereas Pb accumulation rates are highest in the near surface layers of cores from the southern part of the transect. Detailed field studies in 1996 and 1997 focused on the processes governing metal accumulation rates in sediments and metal transport in sediment, water and sawgrass from (a) the Taylor Slough region, ENP (including the Buttonwood Embankment), and (b) from a mercury "hotspot" (elevated fish tissue mercury levels) from WCA-2B. Analyses of these materials are ongoing and results will be presented. Baseline values for metal concentrations in sediments collected in the south Florida study area seem to be attained in core material that is about 100 years old. The geochemistry of upper core material from sediment collection sites further west in the Big Cypress National Preserve show lower levels of trace metals relative to eastern sites and may be reflective of more pristine conditions.

Back to Project Homepage