δ13C signature of organic carbon in estuarine bottom sediment as an indicator of carbon export from adjacent marshes

Abstract

The δ13C signature of organic carbon in estuarine bottom sediment in Louisiana Barataria Basin was used for estimating carbon flux from adjacent marsh. The stable carbon isotope composition of plants, soils and sediments from the basin were determined. The δ13C content of marsh vegetation ranged from -26.3 to -27.8% for C3 freshwater vegetation in the upper basin to -13.0 to -13.3% for C4 vegetation in the lower basin. The δ13C content of the highly organic marsh soils were similar to δ13C content of vegetation present. The δ13C content of organic carbon from bottom sediment of open water bodies ranged from 27.3 in the upper basin (freshwater) to 16.4 in bottom sediment of salt marsh ponds. The13C signature of organic carbon in bottom sediment from saline regions corresponded to the size of the body of water. The smaller salt marsh ponds contain sediment with δ13C values close to that of the C4 plantSpartina alterniflora. Results suggest that phytoplankton rather thanSpartina alterniffora is the likely organic source in bottom sediment of the larger bay near the coast (e.g. Caminada Bay).