This is an introduction to the Interagency Mercury Science Program for the Everglades and South Florida. It is intended to provide an overview of the regional mercury problem and of efforts to determine a remedy. This program is a broad, multidisciplinary effort by scientists from state and federal agencies, state universities and others, working together to understand and address a complex environmental issue. The Science Program is designed to determine: Potential risks to humans and wildlife of mercury in South Florida; How mercury enters the aquatic food chain and concentrates in predators; Chemical and biological pathways for transformation of inorganic mercury into methylmercury; The origin of the mercury in South Florida's atmosphere and waters; How mercury moves through air, water, and soil; Actions that could be taken to reduce levels of mercury in fish and wildlife; Background The Problem in Brief Mercury is a problem in marshes, lakes, rivers and estuaries in many areas of the world, including some of the fresh waters in at least 40 states. Because methylmercury, the most toxic form of mercury, is not readily eliminated by plants and animals, it builds to concentrations much higher than the water or sediment in which the animal lives; the technical term for this is bioaccumulation. For a predator, bioaccumulation is compounded because there is an increasing concentration of methylmercury in each successive link of its aquatic food chain. Bioaccumulation creates a risk of toxicity to fish-eating humans and other predators at the top of a food chain. The amount of risk depends upon how much methylmercury is in the food, how much is eaten and how often. Mercury bioaccumulation is extensive in Florida. Recreational uses are limited in over half of the state's waters because high mercury in fish limits safe consumption. This effect is particularly severe in the Florida Everglades, where health advisories not only recommend reduced or no fish consumption, but the integrity of the ecosystem may be threatened by effects on top predators. Because mercury bioaccumulation may be affected by Everglades water quality and water management, the massive, long-term South Florida Ecosystem Restoration Initiative now underway must address the mercury issue.

Figure 1. Atmospheric Mercury Monitoring Tower. The Florida Atmospheric Mercury Study (FAMOUS) measures atmospheric mercury in air, in rainwater, and attached to particulates suspended in air. (Photo: USEPA)

The Solution in Brief The goal of the South Florida Mercury Science Program is to provide public resource managers with an understanding of mercury risks, and the management tools to reduce these risks to acceptable levels. This goal will be met by carrying out the following tasks: Quantify the physical, chemical, and biological processes that govern mercury transport, its conversion to toxic methylmercury, and its bioaccumulation in South Florida plants and animals; Determine safe mercury exposure levels for aquatic and terrestrial wildlife (safe fish consumption levels for humans are established); Translate these safe levels of exposure to mercury into corresponding values for water and sediment; Convert safe water and sediment values into equivalent rates of supply from all air and water sources; Define management actions or source controls that can limit the rate of conversion of mercury to methylmercury.

Mercury Effects

Mercury in the South Florida aquatic ecosystem comes from atmospheric sources that are both natural and human. The global background of mercury that is thoroughly mixed in the atmosphere has increased by at least two-fold since the Industrial Revolution. Mercury is also emitted from local sources in South Florida. The proportion of Everglades mercury derived from nearby sources is unknown. Work is underway to distinguish local and global contributions to mercury deposition in South Florida (Figure 1). If local emissions near the Everglades are partly responsible for mercury bioaccumulation in the food web, source controls may be applied. Mercury currently being deposited in rain, dust or gaseous forms is augmented by mercury previously deposited and later released from the marsh soil through wet and dry cycles caused by climate and human activities.

Microorganisms transform a portion of the mercury to methylmercury, which bioaccumulates in top predators (Figure 2). Bioaccumulation of mercury in several species of game fish, including the economically important largemouth bass, has made fish consumption advisories necessary to protect human health (Figure 3). These advisories limit beneficial uses of Everglades waters established under the Clean Water Act.

Mercury accumulates to high levels in panthers, raccoons, otters, alligators, turtles, and wading birds. Chronic toxicity can be severe. At least one Florida panther, a severely endangered species, is believed to have died from mercury poisoning. (Figure 4). Mercury was identified as a potential contributing cause of death for two others. Chronic effects of mercury toxicity may harm predator populations by decreasing hunting success, reproduction or life span.

Regional Ecosystem Restoration

Figure 7. South Florida. The Lighter areas on the right are the urban areas along the southeast coast. Inland from the urban areas are remnant Everglades which lie in the Water Conservation Areas. The red area at the top is the Everglades Agricultural Area. Everglades National Park is at the bottom. (Photo: USGS)

Six million people live on the urban fringe of the vast, publicly owned wilderness in South Florida (Figure 7). This area is highly prized and is of economic importance for the recreation that its fish, wildlife and other natural amenities provide. Ecotourism is significant to the regional economy. The Everglades and Big Cypress Swamp are important recreation areas, primarily for catching fish and watching wildlife. Whether they visit it or not, many urban dwellers derive aesthetic pleasure from living next to such an area. Loss of the top predators through mercury toxicity would reduce the ecological integrity of this wilderness and diminish its value to the public.

The ecological health of the South Florida ecosystem depends upon restoration of annual and seasonal variations in water flows and depths in the remnant Everglades. The creation of new water reservoirs; alteration of marsh water depths, periods of inundation and flow velocities; nutrient removal; and other changes may influence factors that affect methylmercury bioaccumulation. Neither the direction nor magnitude of changes in methylmercury bioaccumulation due to these restorative efforts is known.

The value the public sets on the Everglades is reflected by current efforts to correct damage done by water management efforts conducted in a less environmentally sensitive era. At the state level, private interests (agriculture, development, environment, & others) and agencies of federal, state, and local governments have formed a coalition, the Governor's Commission for a Sustainable South Florida, to develop and implement a regional ecosystem restoration plan. There is a complementary effort at the federal level where federal and state agencies, tribal interests and local governments are working together on the Task Force on South Florida Ecosystem Restoration established by the federal 1996 Water Resources Development Act.

State and federal commitments for capital investment in restoration projects already underway total $1.82 billion. Including infrastructure and land acquisition, the proposed 1997 budget for federal agencies, is $271 million. To alleviate eutrophication caused by nutrients in agricultural storm-water (Figure 5), 43,000 acres of man-made wetlands called Stormwater Treatment Areas (STAs) will be constructed. The U.S. Army Corps of Engineers has completed a Programmatic Environmental Impact Statement for these restorative measures. Intensive studies of mercury in STAs are underway in the pilot-scale Everglades Nutrient Removal Project (ENR) to ensure that the potential effects on mercury methylation in STAs and on downstream waters are thoroughly examined and understood.

The State of Florida adopted the Everglades Forever Act in 1994. This act requires an examination of the water quality standard for mercury and the development of a new standard if the existing one is inadequate. This Science Program will satisfy that requirement.

Much broader efforts to restore seasonal water depths and flows over much of the Everglades are in the early planning stage. Toward this effort, the Corps has finished the Reconnaissance Report for the Comprehensive Review Study of the Central and South Florida Project authorized by Congress.

Next: Mercury Science Program

Related information:

SOFIA Project: Aquatic Cycling of Mercury in the Everglades (ACME)