Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) was used to identify the qualitative differences between dissolved organic matter (DOM) in fen and bog porewaters from the Red Lake II system in the Glacial Lake Agassiz Peatlands (GLAP) of northern Minnesota. Approximately 80% of the molecular composition in surface porewater was maintained throughout the upper portion of the bog profile (0.17-2.50. m). The qualitative stability of the composition of the DOM was accompanied by a quantitative increase in dissolved organic carbon (DOC) with depth. The composition of DOM in the fen was significantly different at depth, with slightly varying DOC levels. Aromaticity index (AI) values were used to identify condensed aromatic and phenol-type compounds in the porewater of both peatlands. Surface bog and deep fen DOM had surprisingly similar molecular composition. Differences in enzymatic degradation rates via phenol oxidase in the bog and surface fen horizons, slower transport down the bog vertical profile and the presence of a stratum of Sphagnum-woody peat at depth in the fen are suggested as being responsible for the observed variations in DOM composition.
Bibliographical noteFunding Information:
The work was supported by the National Science Foundation , Grant No. EAR0628349 . Mass spectra were obtained at the National High-Field Ion Cyclotron Resonance Mass Spectrometry Facility (NSF CHE-99-09502) at the National High Magnetic Field Laboratory in Tallahassee, FL. The manuscript was developed after lengthy discussions with the GLAP working group that included D. Siegel, D. Burdige, E. Corbett and M. Sarkar. We also thank B. Vanmiddlesworth for contributions to the development of data analysis programs written for both PYTHON and MATLAB. The manuscript was significantly improved in response to the thoughtful comments of two anonymous reviewers.
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