Decadal carbon decomposition dynamics in three peatlands in Northern Minnesota
The uppermost portion of the peat profile, an area of active diagenetic processes, is exceedingly important for understanding peatland dynamics and the diagenesis and geochemistry of atmospherically-deposited materials. We investigated high resolution carbon (C) accrual and peat decomposition rates at two Sphagnum-rich ombrotrophic bogs and one fen in northern Minnesota, USA by analyzing 1 cm increments from 30 cm thick intact frozen blocks of peat soil. We conducted radiocarbon analysis of Sphagnum cellulose to determine peat age and net C accumulation at each depth interval. Calibrated peat ages were determined using CALIBomb and a compilation of calibration datasets for the pre-bomb period. We fit data with a negative exponential accumulation model and used model-derived parameters to estimate net primary productivity (NPP) and a peat decomposition rate constant k. FTIR spectroscopy and C:N were used to derive humification indices and to chemically characterize the peat. NPP ranged from 180 to 266 g C m−2 year−1, k ranged from 0.015 to 0.019 year−1. Net C accumulation rates ranged from 112 to 174 g C m−2 year−1 at 25 years and 70 to 113 g C m−2 year−1 at 50 years. Mass loss was up to 55% during the first 50 years of peat accumulation. Decomposition is greater at depth in the bogs—where 25 cm of peat correspond to 55 years of peat accumulation—than in the fen, where peat age is approximately 25 years at 25 cm depth. Information on fine-scale variations in peat mass decomposition and loss across ombrotrophic bogs and a fen help interpret other diagenetic processes in peatlands.
KeywordsPeatland Carbon accrual Radiocarbon FTIR Sphagnum moss Humification indices
This work was funded through a Whittier College Faculty Research Grant to C.F. and the work of students was supported in part through Exception Funds Granted to C.F. by Whittier College. A portion of this work was supported by Lawrence Livermore National Laboratory, Laboratory Research and Development project 14-ERD-038 (under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, LLNL-JRNL-749770). We thank S. Sebestyen and R. Kolka for early feedback on the manuscript, D. Kyllander for helping with site identification and core extraction and T. Sellie for help subsampling the cores, L. Aguayo, M. Voegtle, and J. Lindvai for laboratory work, C. Hicks Pries for her advice on cellulose extraction procedures and carbon accumulation model fitting, N. Jelinski for statistical advice, and M. Tfaily and C. Bauer for support concerning IR techniques. We thank our collaborators at the Marcell Experimental Forest and the US Forest Service Northern Research Station for site access and support.
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