MONITORING AND MASS BUDGET FOR MERCURY IN THE EVERGLADES NUTRIENT REMOVAL PROJECT

The Everglades Nutrient Removal Project (ENRP) is a 1,545-ha prototype wetland constructed to test a larger system of stormwater-treatment a reas that is being used to remove agricultural nutrients and help rest ore the remnant Everglades. Concerns that the ENRP may lead to mercury bioaccumulation as observed in other newly created reservoirs resulte d in an effort to construct a mercury mass budget and measure bioaccum ulation in aquatic organisms. For the first 2 years of operation, tota l mercury (THg) and methylmercury (MeHg) concentrations in water decre ased significantly a short distance into the ENRP, probably through pa rticle settling. During both years, THg concentrations in largemouth b ass were about 0.1 mu g/g throughout the ENRP while the adjacent Water Conservation Area bass were at or above the state health advisory lev el of 0.5 mu g/g. THg levels in mosquitofish were lower than levels fo und in bass, and mosquitofish mercury concentrations in the interior o f the ENRP were significantly lower than the inflow and outflow sites. The major THg pool was the sediment while less than 1% the total mass was stored in vegetation, water, and fish. The major MeHg pool also w as the sediment but vegetation, water, and fish were significant fract ions. Mass budget estimates showed the inflow pump and rainfall to be the major sources of THg, while the outflow pump was the major output. The inflow pump was the major source of MeHg while the outflow pump w as the major output. Evasion of elemental mercury estimated by the sta gnant-him model indicated a minor loss, but field measurements over ca ttails suggested that evasion may be the major pathway. When all input s and outputs were considered, the ENRP removed about 70% of the THg a nd MeHg masses in the first 2 years of operation.