ENVIRONMENTAL BIOGEOCHEMISTRY OF MERCURY IN FLORIDA EVERGLADES: 1989 – 2003

For most aquatic ecosystems, there is compelling evidence is that atmospheric sources constitute the primary inputs of mercury (Hg) to most water bodies. Given this feature of the multi-media Hg cycle, the question of whether changes in atmospheric loadings have induced corresponding changes in aquatic ecosystems ? Or, restated, do current trends in fish Hg concentrations reflect changes in atmospheric deposition rates, including changes in the strength of the sources and not simply meteorological variability, or do the trends reflect other factors? In 1989 monitoring by state agencies found Hg in largemouth bass from the Florida Everglades to average in excess of 2 ppm – well above all health-based standards of that day. Subsequent to an apparent peak in the mid-1990’s, consistent declines in largemouth bass Hg concentrations throughout Florida have been observed, including declines in portions of the Everglades of ca. 60% (Fig. 1, Lange, 2001). Likewise, Frederick (2001) has observed a similar decline in Hg in wading birds in the Everglades. Since atmospheric deposition is the major source of Hg to the Everglades, the question of whether the observed declines in biota Hg concentrations are related to declines in local emissions arises. For this to be true, concomitant changes in atmospheric deposition rates of Hg should be evident for the same time period. This analysis explores whether trends in atmospheric deposition in south Florida correspond to trends in atmospheric emissions of Hg, and whether the trends in biota Hg concentrations can be related to changing emission and deposition levels.