Carbon Isotopic Compositions of Plants and Sediments of Tide Marshes in the San Francisco Estuary

Wetland sediments surrounding the San Francisco Bay Estuary contain a rich history of environmental change which can aid predictions of potential responses to future environmental change. Here we present results of a study of the stable carbon isotopic composition of modern surface sediments as they relate to the existing plant cover. The results indicate a strong correlation between the modern plant cover and the δ13C value of underlying surface sediments (RMS = 1.331). Reasons for residual differences between predicted and observed isotopic values of the surface soils include intraspecific changes in δ13C values of C3 plants, contributions to the carbon pool by algae, and effects of diagenesis on δ13C value of plant matter. The goal of this research is to provide a basis for interpreting isotopic data obtained from sediment cores in terms of changes in vegetation resulting from changes in environmental conditions.