Sediment and soil organic matter source assessment as revealed by the molecular distribution and carbon isotopic composition of n-alkanes

Authors

Ralph Mead, Environmental Geochemistry Group, Southeast Environmental Research Center and Department of Chemistry and Biochemistry, Florida International UniversityFollow
Yunping Xu, Environmental Geochemistry Group, Southeast Environmental Research Center and Department of Chemistry and Biochemistry, Florida International UniversityFollow
Jodi Chong, Environmental Geochemistry Group, Southeast Environmental Research Center and Department of Chemistry and Biochemistry, Florida International University
Rudolf Jaffe´, Southeast Environmental Research Center, Department of Chemistry and Biochemistry, Florida International University,Follow

Abstract

The assessment of organic matter (OM) sources in sediments and soils is a key to better understand the biogeochemical cycling of carbon in aquatic environments. While traditional molecular marker-based methods have provided such information for typical two end member (allochthonous/terrestrial vs. autochthonous/microbial)-dominated systems, more detailed, biomass-specific assessments are needed for ecosystems with complex OM inputs such as tropical and sub-tropical wetlands and estuaries where aquatic macrophytes and macroalgae may play an important role as OM sources. The aim of this study was to assess the utility of a combined approach using compound specific stable carbon isotope analysis and an n-alkane based proxy (Paq) to differentiate submerged and emergent/terrestrial vegetation OM inputs to soils/sediments from a sub-tropical wetland and estuarine system, the Florida Coastal Everglades.

Results show that Paq values (0.13–0.51) for the emergent/terrestrial plants were generally lower than those for freshwater/marine submerged vegetation (0.45–1.00) and that compound specific δ¹³C values for the n-alkanes (C₂₃ to C₃₁) were distinctively different for terrestrial/emergent and freshwater/marine submerged plants. While crossplots of the Paq and n-alkane stable isotope values for the C₂₃n-alkane suggest that OM inputs are controlled by vegetation changes along the freshwater to marine transect, further resolution regarding OM input changes along this landscape was obtained through principal component analysis (PCA), successfully grouping the study sites according to the OM source strengths. The data show the potential for this n-alkane based multi-proxy approach as a means of assessing OM inputs to complex ecosystems.

Comments

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Recommended Citation

Mead, R.N., Y. Xu, J. Chong, R. Jaffe. 2005. Sedimentary organic matter source assessment in a sub-tropical wetland and estuarine environment using the molecular distribution and carbon isotopic composition of n-alkanes. Organic Geochemistry 36(3): 363-370.