ACCUMULATION OF ANTHROPOGENIC TRACE METALS IN SEDIMENTS OF THREE NORTH-CENTRAL FLORIDA LAKES

Anthropogenic activities impact trace metal cycling on regional and global scales. Lake sediments are excellent archives for recording atmospheric deposition of such trace metals. Characteristics of individual lakes, however, are thought to influence the distribution of trace metals in lake deposits. Sediment cores from three nearby lakes in Goldhead Branch State Park, north-central Florida, were used to evaluate the accumulation of trace metals, including total anthropogenic metal flux and depositional patterns of metal concentrations, and any possible inter-lake disparity. The lakes differ with respect to several variables, including size, depth, trophic state, stage variability and sediment composition. Lake Sheelar is oligotrophic, with an area of 0.073 km², a maximum depth of 19.8 m, and an historic lake stage range of 2.5 m. Little Lake Johnson is oligotrophic, with a lake level range of 7 m, an average maximum depth and area of 4.5 m and 0.11 km², respectively. The mesotrophic Pebble Lake is the most astatic water body in this karstic lake region of Florida, with a 12 m range of lake level and an area of only 0.016 km² at high stage. Both Lakes Pebble and Little Johnson have been dry for the past year as a consequence of local drought conditions. Short sediment cores were collected near the center of each lake and sampled at 2-cm intervals. Sediment age/depth relations were determined using ²¹⁰Pb dating methods. Organic matter was removed by combustion and remaining ash was digested and analyzed using an ICP-MS for total trace metal concentrations. All three lakes in this relatively isolated state park display evidence of anthropogenically sourced trace metal deposition. Since 1900, concentrations of Pb, Cu, Ni, Sn, Zn, V, Sb, Bi, and Cr have increased. Lead concentrations peak between 1970 and 1980, tracking the use of leaded gasoline. The stratigraphic profile of Pb concentration varies among lakes, but this may simply reflect intra-lake differences in bulk sedimentation rate.