MERCURY ACCUMULATION TRENDS IN FLORIDA EVERGLADES AND SAVANNAS MARSH FLOODED SOILS

Global and regional increases in atmospheric mercury (Hg) concentratio ns have previously been identified as the cause of increased mercury a ccumulation rates in north temperate lakes in Sweden, Wisconsin, and M innesota. Atmospheric deposition can often account for elevated Hg con centrations in fish from these systems. Mercury levels in sportfish co llected from some areas of the Florida Everglades and Savannas Marsh e xceed limits that are acceptable for human consumption. Forty five soi l cores and soil grab samples were retrieved from the Everglades and S avannas Marsh wetlands. Eighteen sediment cores were dated radiochemic ally with Pb-210 and Cs-137 using gamma-ray spectroscopy to determine modem and historic mercury accumulation rates for these subtropical we tland systems. Recent (''post-l985'') Hg accumulation rates averaged 5 3 mu g m(-2) y(-1) (23 to 141,n = 18) corresponding to an average-rate increase of 4.9 times (1.6 to 19.1) over those observed around the tu rn of the century. This accumulation seems to result more from either global or regional atmospheric deposition rather than from lateral tra nsport via overlying surface water. The trends for mercury accumulatio n match those reported for lakes in Sweden and the northern United Sta tes, even though these systems are distinctly different in their clima te, vegetational composition,and location. We provide the first data o n accumulation of mercury in subtropical wetland systems, and demonstr ate the feasibility of radiochemical dating of wetland sediment.