Chemical characterization of dissolved organic nitrogen in an oligotrophic subtropical coastal ecosystem

Authors

Nagamitsu Maie, Southeast Environmental Research Center, and Department of Chemistry and Biochemistry, Florida International UniversityFollow
Kathleen J. Parish, Southeast Environmental Research Center, and Department of Chemistry and Biochemistry, Florida International UniversityFollow
Akira Watanabe, Department of Cycling Resources, School of Bioagricultural Sciences, Nagoya UniversityFollow
Heike Knicker, Lehrstuhl für Bodenkunde, Technische Universität München
Ronald Benner, Department of Biological Sciences and Marine Science Program, University of South Carolina
Tomonori Abe, Department of Cycling Resources, School of Bioagricultural Sciences, Nagoya University
Karl Kaiser, Department of Biological Sciences and Marine Science Program, University of South Carolina
Rudolf Jaffe´, Southeast Environmental Research Center, and Department of Chemistry and Biochemistry, Florida International UniversityFollow

Abstract

Water samples were collected from rivers and estuarine environments within the Florida Coastal Everglades (FCE) ecosystem, USA, and ultrafiltered dissolved organic matter (UDOM; 1 kDa) was isolated for characterization of its source, bioavailability and diagenetic state. A combination of techniques, including ¹⁵N cross-polarization magic angle spinning nuclear magnetic resonance (¹⁵N CPMAS NMR) and X-ray photoelectron spectroscopy (XPS), were used to analyze the N components of UDOM. The concentrations and compositions of total hydrolysable amino acids (HAAs) were analyzed to estimate UDOM bioavailability and diagenetic state. Optical properties (UV–visible and fluorescence) and the stable isotope ratios of C and N were measured to assess the source and dynamics of UDOM. Spectroscopic analyses consistently showed that the major N species of UDOM are in amide form, but significant contributions of aromatic-N were also observed. XPS showed a very high pyridinic-N concentration in the FCE–UDOM (21.7 ± 2.7%) compared with those in other environments. The sources of this aromatic-N are unclear, but could include soot and charred materials from wild fires. Relatively high total HAA concentrations (4 ± 2% UDOC or 27 ± 4% UDON) are indicative of bioavailable components, and HAA compositions suggest FCE–UDOM has not undergone extensive diagenetic processing. These observations can be attributed to the low microbial activity and a continuous supply of fresh UDOM in this oligotrophic ecosystem. Marsh plants appear to be the dominant source of UDOM in freshwater regions of the FCE, whereas seagrasses and algae are the dominant sources of UDOM in Florida Bay. This study demonstrates the utility of a multi-technique and multi-proxy approach to advance our understanding of DON biogeochemistry.

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

Maie, N., K. Parish, A. Watanabe, H. Knicker, R. Benner, T. Abe, K. Kaiser, R. Jaffe. 2006. Characterization of dissolved organic nitrogen in an oligotrophic subtropical coastal ecosystem. Geochimica et Cosmochimica Acta 70(17): 4491-4506.