MERCURY ACCUMULATION TRENDS IN FLORIDA EVERGLADES AND SAVANNAS MARSH FLOODED SOILS

Global and regional increases in atmospheric mercury (Hg) concentrations have previously been identified as the cause of increased mercury accumulation rates in north temperate lakes in Sweden, Wisconsin, and Minnesota. Atmospheric deposition can often account for elevated Hg concentrations in fish from these systems. Mercury levels in sportfish collected from some areas of the Florida Everglades and Savannas Marsh exceed limits that are acceptable for human consumption. Forty five soil cores and soil grab samples were retrieved from the Everglades and Savannas Marsh wetlands. Eighteen sediment cores were dated radiochemically with Pb-210 and Cs-137 using gamma-ray spectroscopy to determine modem and historic mercury accumulation rates for these subtropical wetland systems. Recent (''post-l985'') Hg accumulation rates averaged 53 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 turn of the century. This accumulation seems to result more from either global or regional atmospheric deposition rather than from lateral transport via overlying surface water. The trends for mercury accumulation match those reported for lakes in Sweden and the northern United States, even though these systems are distinctly different in their climate, vegetational composition,and location. We provide the first data on accumulation of mercury in subtropical wetland systems, and demonstrate the feasibility of radiochemical dating of wetland sediment.