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LACUSTRINE RECORDS OF ENVIRONMENTAL CHANGE IN SOUTH GEORGIA my page
In conjunction with colleague Jeff Tepper (Valdosta State University) I am currently investigating lacustrine sedimentary records of environmental change near Valdosta, GA. This work has been conducted at Lake Louise, GA a 5 ha blackwater lake owned by VSU. Lake Louise has figured prominently in botanical reconstructions for the southeastern United States (Watts, 1971; Ecology, 52:676-690), and Jeff and I have had several undergraduate students examine sediments from this lake. Our work has focussed on two aspects of the sedimentary record. Jeff is currently examining geochemical records preserved within a 9.2 m core. He is currently investigating the partitioning of trace elements within the clastic, diatom, and organic fraction of sediment in the core. My interests focuss on recent records of change associated with the construction of Interstate 75 across the lake's only inflow channel. This includes studies of sediment focussing within the lake, and recent 210-Pb chronologies of sedimentation.
Preparing to Core Lake Louise Rubble Layer at 7.5 m depth.	*Trace Element Stratigraphy of Sediment and Freshwater Diatom Frustules from Lake Louise, GA: An 8,500 Year Paleoenvironmental Record from South Central Georgia.* Lake Louise is a 5.4 ha, 6.5 m deep humic lake located in south-central Georgia. This study focuses on the origins and paleoenvironmental implications of geochemical and floristic changes observed in the upper 700 cm (~8500 years) of a core recovered from the center of the lake. This sediment consists of algal gyttja (40-60% organic matter, 20-40% biogenic silica, ~20% terrigenous sediment) and displays millennial-scale geochemical trends that correlate with variations in diatom assemblage and with previously recognized shifts in pollen spectra (Watts, 1971). Bulk sediment trace element concentrations (Sr, Ba, Ti, V, Co, Cr, Ni, Cu Zn, Pb) decrease upward in the core from 700 - 400 cm (~2000 BP), and then remain low until ~1800 AD (onset of European settlement). Comparisons of bulk sediment data with paired analyses of separated diatom frustules and terrigenous sediment reveal that: (1) Trace elements are hosted primarily in the organic fraction (>85% of transition metals, >50% Sr, Ba), (2) Variations in bulk sediment composition are principally controlled by changes in the composition of the organic fraction, and (3) The diatom frustules and clay-sized sediment fractions, although containing <10% each of the total inventory of most trace elements, display chemical trends that parallel those of the bulk sediment. Because planktonic diatoms and lacustrine organic matter incorporate trace elements directly from the water column, we conclude that the observed trends reflect long-term variations in water chemistry. Floristic data support this conclusion: declining trace element levels are accompanied by a shift from an alkaliphilous diatom assemblage in the oldest sample to an assemblage in younger samples dominated by taxa that favor dilute waters. These chemical and floristic trends may record a drying of the region during the mid-Holocene, with resultant decreases in lake level, organic sediment preservation and groundwater input, and enhanced biological element scavenging. *Reference:* TEPPER, Jeffrey H., Dept. of Physics, Astronomy, & Geosciences, Valdosta State University, Valdosta, GA 31698, jtepper@valdosta.edu; WOLFE, Alexander P., INSTAAR, University of Colorado, Boulder, CO 80309