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Multi-proxy Records of Environmental Changes in a Freshwater Wetland in Louisiana during the Late Holocene

This study reports on a palynology-based multi-proxy analysis of a 360 cm sediment core retrieved from a freshwater marsh near Lake Pontchartrain in southern Louisiana, U.S.A. The site has experienced significant geological and eco-logical alterations during the late Holocene. Palynological and geochemical data suggest that four stages of ecological succession occurred during the last 5,000 years. The site changed from an oyster reef in the back-barrier system (5.0-4.0 cal yr BP) with elevated marine elemental concentration of Ca to a transitional stage (4.0-3.5 cal yr BP) with high Zr/Br ratio, and then to a lake stage (3.5-2.0 cal yr BP) during the St. Bernard delta complex with increasing terrestrial elemental concentration of Zr. It finally changed to a Sagittaria-Typha freshwater marsh (2.0 cal yr BP to present) with elevated Br concentration. The high charcoal concentration suggests an intense fire event that occurred prior to the establishment of the Sagittaria-