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Geochemistry of sediments from coastal marshes of Louisiana

August 1, 1996

As a part of the U.S. Geological Survey Global Change and Climate History Program we have been studying the biogeochemistry of coastal marshes in Terrebonne Basin, Louisiana. Louisiana has about 40 percent of the coastal wetlands in the conterminous U.S. and it is losing wetlands at one of the highest rates in the U.S. with the conversion of about 65 km2/yr of marsh to open water (Britsch and Dunbar, 1993). The losses have been attributed to human and natural causes including saltwater intrusion through man-made canals, reduced sediment input, and regional subsidence. The net effect of these influences is to change the salinity of interior marshes in a fashion similar to a eustatic sea level rise. We are studying the cycling of carbon, sulfur, and other elements in sediments, waters, and marsh macrophytes in fresh, intermediate/brackish, and saltwater marshes in order to better understand how sea level rise, one aspect of global change, will influence and in turn be influenced by cycling of these elements. By characterizing the critical biogeochemical processes and the recent past environments in these rapidly changing marshes, we can improve predictions of future changes and interpretations of the historic geologic record in similar environments.

In this report we describe our coastal marsh study sites in Louisiana, the types of samples collected, the collection methods, the chemical analysis methods, and selected chemical analysis results. Also included are summaries of the project quality control results. The raw chemical analysis results are provided in this report without interpretation. Interpretations will be provided in subsequent reports.