Fate of Airborne Contaminants in Okefenokee National Wildlife Refuge

Abstract

Designation of Okefenokee National Wildlife Refuge as a Class I Air Quality Area (given the highest level of protection possible from air pollutants under the Clean Air Act Amendments of 1977) affords mandatory protection of the Refuge's airshed through the permit-review process for planned developments. Rainfall is the major source of water to the swamp, and potential impacts from developments to the airshed are high. To meet management needs for baseline information, chemical contributions from atmospheric deposition and partitioning of anions and cations, with emphasis on mercury and lead, in the various matrices of the Swamp were determined between July 1993 and April 1995. Chemistry of rainfall was determined on an event basis from one site located at Refuge Headquarters. Field samples of surface water, pore water, floc and sediment were collected from four locations on the Refuge: Chesser Prairie, Chase Prairie, Durden Prairie, and the Narrows. A sediment core sample was collected from the Refuge interior at Bluff Lake for aging of mercury deposition. Rainfall was acidic (pH 4.8) with sulfate concentrations averaging 1.2 mg/L and nitrate averaging 0.8 mg/L. Lead in rainfall averaged 1 ?g/L and total and methylmercury concentrations were 11.7 ng/L and 0.025 ng/L, respectively. The drought of 1993 followed by heavy rains during the fall and winter caused a temporary alteration in the cycling and availability of trace-elements within the different matrices of the Swamp. Surface water was acidic (pH 3.8 to 4.1), dilute (specific conductance 35-60 ?S/cm), and highly organic (DOC 35-50 mg/L). Sediment and floc were also highly organic (>90%). Total mercury averaged 3.6 ng/L in surface water, 9.0 ng/L in pore water and about 170 ng/g in floc and sediments. Mercury bioaccumulated in the biota of the Refuge: fish fillets (Centrarchus macropterus, Esox niger, Lepomus gulosus and Amia calva) had >2 ?g/g dry weight, alligators (Alligator mississippiensis) >4 ?g/g dry weight in liver and kidney, and raccoons (Procyon lotor) >16 ?g/g dry weight in the liver and kidney. Lead averaged 1 ?g/L in rainfall, 6.6 ?g/L in surface water, 9.8 ?g/L in pore water, 12.3 ?g/g in floc and 12.5 ?g/g in sediments. Lead in fish muscle was ~0.1 ?g/g and >1.2 ?g/g in bone, alligator kidney had 1.5 ?g/g lead and liver had 3.8 ?g/g; raccoon kidney and liver averaged about 1 ?g/g. Historical patterns of mercury deposition based on 210Pb aging of the core sample showed mercury increased from pre-1800 concentrations of <250 ng/g to >500 ng/g in the 1950s, with a subsequent decline to current levels. Lead concentrations in the core sample followed a similar pattern as that of mercury. Okefenokee Swamp serves as a sump for the cations and anions deposited through rainfall. Although mercury and lead levels in the biota are not currently acutely hazardous, concentrations are high enough to cause adverse chronic effects on behavioral, physiological or reproductive functions of resident biota, especially piscivorous species. To protect trust resources associated with the Refuge, activities and developments in the airshed that have the potential to increase atmospheric contamination, especially for lead and mercury, should be curtailed.