title: Use of ESI-FTICR-MS to Characterize Dissolved Organic Matter in Headwater Streams Draining Forest-Dominated and Pasture-Dominated Watersheds.
abstract: Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) has proven to be a powerful technique revealing complexity and diversity of natural DOM molecules, but its application to DOM analysis in grazing-impacted agricultural systems remains scarce. In the present study, we presented a case study of using ESI-FTICR-MS in analyzing DOM from four headwater streams draining forest- or pasture-dominated watersheds in Virginia, USA. In all samples, most formulas were CHO compounds (71.8-87.9%), with other molecular series (CHOS, CHON, CHONS, and CHOP (N, S)) accounting for only minor fractions. All samples were dominated by molecules falling in the lignin-like region (H/C = 0.7-1.5, O/C = 0.1-0.67), suggesting the predominance of allochthonous, terrestrial plant-derived DOM. Relative to the two pasture streams, DOM formulas in the two forest streams were more similar, based on Jaccard similarity coefficients and nonmetric multidimensional scaling calculated from Bray-Curtis distance. Formulas from the pasture streams were characterized by lower proportions of aromatic formulas and lower unsaturation, suggesting that the allochthonous versus autochthonous contributions of organic matter to streams were modified by pasture land use. The number of condensed aromatic structures (CAS) was higher for the forest streams, which is possibly due to the controlled burning in the forest-dominated watersheds and suggests that black carbon was mobilized from soils to streams. During 15-day biodegradation experiments, DOM from the two pasture streams was altered to a greater extent than DOM from the forest streams, with formulas with H/C and O/C ranges similar to protein (H/C = 1.5-2.2, O/C = 0.3-0.67), lipid (H/C = 1.5-2.0, O/C = 0-0.3), and unsaturated hydrocarbon (H/C = 0.7-1.5, O/C = 0-0.1) being the most bioreactive groups. Aromatic compound formulas including CAS were preferentially removed during combined light+bacterial incubations, supporting the contention that black carbon is labile to light alterations. Collectively, our data demonstrate that headwater DOM composition contains integrative information on watershed sources and processes, and the application of ESI-FTICR-MS technique offers additional insights into compound composition and reactivity unrevealed by fluorescence and stable carbon isotopic measurements.
authors.affiliation: Department of Geological Sciences, University of Alabama, Tuscaloosa, Alabama, United States of America.
authors.forename: YueHan
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Department of Geological Sciences, University of Alabama, Tuscaloosa, Alabama, United States of America.
authors.forename: Xiaping
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia, United States of America.
authors.forename: Rajaa
authors.initials: R
authors.lastname: Mesfioui
authors.affiliation: Aquatic Biogeochemistry Laboratory, Department of Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, Ohio, United States of America.
authors.forename: James E
authors.initials: JE
authors.lastname: Bauer
authors.affiliation: Department of Biology, College of William and Mary, Williamsburg, Virginia, United States of America.
authors.forename: R M
authors.initials: RM
authors.lastname: Chambers
authors.affiliation: Department of Physical Sciences, Virginia Institute of Marine Sciences, Gloucester Point, Virginia, United States of America.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Canuel
authors.affiliation: Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia, United States of America.
authors.forename: Patrick G
authors.initials: PG
authors.lastname: Hatcher
mesh_terms: D004784:Environmental Monitoring; D065928:Forests; D005583:Fourier Analysis; D008027:Light; D009930:Organic Chemicals / Q000737:chemistry*; D045483:Rivers / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D009930:Organic Chemicals