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St. Petersburg Coastal and Marine Science Center
Natural Subsidence and Sea-Level Rise
Geologic proxies may shed light on long-term environmental trends and stability of the Louisiana coastal marsh. The combined processes of accretion, sea-level rise and subsidence influence wetland elevation and determine marsh stability. Microfossils, such as foraminifera (fig. 1) and diatoms (fig. 2), are sensitive to environmental conditions, and present meaningful long-term proxies for investigating wetland stability and persistence. Once protocols are established, these geologic proxies are valuable for rapid assessment of environmental trends.
The USGS is investigating landscape change in coastal wetlands using microfossil assemblages and physical characteristics in marsh cores as proxies for storm impact, subsidence, and sea-level rise. Surface and down-core microfossil distributions will be correlated with sedimentologic and stratigraphic parameters to identify changes in environmental conditions. The initial study area will focus on southwest Louisiana, where rapid subsidence and erosion of wetlands is resulting in unprecedented rates of sea level rise.
The project goals are to:
Paleoecological and sedimentological analyses are conducted on several coastal marsh sediment cores. Sediment core sites are selected to represent a gradient of saline to brackish marsh. Cores are X-rayed and sampled for microfossil assemblages, grain-size, bulk density, organic carbon, and radioisotopes (210Pb and 137Cs). Statistical analyses of downcore abundance curves for microfossils and sedimentological data are examined with chronology data to isolate proxies most clearly indicative of marsh accretion, storm-impact, subsidence, and sea-level rise.
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