A multi-proxy approach to investigating the latest Holocene (~4,500 yrs. BP) vegetational history of Catahoula Lake, Louisiana

Abstract

A multi-proxy investigation of sediments examined from Catahoula Lake, Louisiana has provided a record of late-Holocene vegetational changes, related to both hydrology and climate. This study integrates data from phytoliths, pollen, stable isotopes, magnetic susceptibility, and core sediment analysis. A modern phytolith analog assessed the phytoliths production in local plants and their modern soil sample distribution within the established lake vegetation zones. Fifty of the 76 species produced both distinctive and redundant phytoliths. The modern soil sample database indicates that phytoliths produced from both monocotyledon and dicotlyledon plant groups prove useful in distinguishing between forest and grassland communities and identifying preservational bias in phytolith types. This analog was then used in conjunction with additional proxies, to interpret downcore data. Three sediment cores (from 3.2 - 4.3 meters in length) were retrieved from Catahoula Lake. Sediment analysis, magnetic susceptibility, and stable isotopic data were determined. These data sets indicate alternating wet and dry periods, suggesting that both changes in local and regional hydrology and climate impact detrital and organic input into the lake. Sediment cores, CLR1 and CLR3, were radiocarbon dated and provide pollen and phytolith evidence for dynamic changes in lacustrine hydrology and vegetation during the last ~4,500 years B.P. The transition out of the Hypsithermal period (~4,500 to 3,700 yrs B.P.) is characterized by pollen assemblages representative of mixed bottomland hardwood forest and swamp forest. By 3,500 to 2,000 years B.P., pollen and phytolith assemblages indicate relatively stable lake conditions as evidenced by increases in flood-tolerant taxa and stable shoreline communities. Periods of lower, fluctuating lake levels existed from 2,000 yrs B.P. to present, with pollen and phytolith assemblages displaying an overall increase in wetland taxa; most notably Cyperaceae and Sagittaria sp. and moderately flood-tolerant species (i.e. Salix sp. and Carya aquatica). In addition, archaeological settlement patterns documented around the lakebed are strongly associated with changes in lake hydrology and vegetation, with increases in grasses and herbs documented during periods of increased site habitation. The first documentation of Zea mays in the Catahoula Lake area was documented at 1,600 years B.P., indicating small-scale agriculture during this period.