PHYTOLITH ANALYSIS AND SEDIMENT CHARACTERISTICS OF CATAHOULA LAKE, LOUISIANA: PRELIMINARY RESULTS

Catahoula Lake, the largest, natural freshwater lake in Louisiana, is a unique lake characterized by widely fluctuating seasonal water levels, which in turn influence the vegetation in and around the lakebed. This water regime may have persisted in the lake for thousands of years during which sediment and abundant microfossils (e.g. diatoms, pollen, sponge spicules, and phytoliths) have been deposited. These microfossil data paired with the record of sedimentary characteristics such as gamma-ray density (GRD), loss-on-ignition (LOI), and magnetic susceptibility (MS) are being studied with the goal of determining the environmental and climatic history of the lake. Three sediment cores have been collected from the lakebed, CLR1 (3.8 meters), CLR2 (4.6 m) and CLR3 (3.4 m). The longest and southernmost core, CLR2, is particularly interesting in that its' location in the lake is heavily impacted by fluvial input from Little River and out flowing Saline Bayou. Microfossil assemblages and sediment data permit the core to be divided into 2 distinct units. MS and GRD data suggest that the upper 1.8 m is predominately lacustrine sediments of alternating clay and fine silt. A distinct increase in GRD and decreasing organic carbon content in the lower portion of the core suggests increased fluvial influence. There is however, a brief return to lacustrine sediment deposition from 3.4 to 3.8 m. Microfossil abundance, diversity, and preservation also fluctuate throughout the core. Most notably a decrease in pollen, diatoms, freshwater sponge spicules, and chrysophycean cysts strongly correlates with increasing GRD and decreasing organic carbon content. Phytoliths, on the other hand, were recovered throughout the core exhibiting a decrease in grass silica short cells (GSSC) and increase in more robust grass long cells (e.g. bulliforms and elongates) and dicotlyledon-types (e.g. blocky and polyhedral) in conjunction with above-mentioned sedimentological changes. These variations in sedimentary fabrics and microfossil assemblages may in part be due to the influence of suspended sediment washed into the lake from Little River and Saline Bayou, which reverses flow during flood events. Chronologies are being established using radiocarbon dating on macrofossil material and 210Pb analyses on the uppermost sediments.