Northern peatlands are an important source for greenhouse gases, but their capacity to produce methane remains uncertain under changing climatic conditions. We therefore analyzed a 43 year time series of the pore-water chemistry to determine if long-term shifts in precipitation altered the vertical transport of solutes within a large peat basin in northern Minnesota. These data suggest that rates of methane production can be finely tuned to multidecadal shifts in precipitation that drive the vertical penetration of labile carbon substrates within the Glacial Lake Agassiz Peatlands. Tritium and cation profiles demonstrate that only the upper meter of these peat deposits was flushed by downwardly moving recharge from 1965 to 1983 during a Transitional Dry-to-Moist Period. However, a shift to a moister climate after 1984 drove surface waters much deeper, largely flushing the pore waters of all bogs and fens to depths of 2 m. Labile carbon compounds were transported downward from the rhizosphere to the basal peat at this time producing a substantial enrichment of methane in Δ14C with respect to the solid-phase peat from 1991 to 2008. These data indicate that labile carbon substrates can fuel deep production zones of methanogenesis that more than doubled in thickness across this large peat basin after 1984. Moreover, the entire peat profile apparently has the capacity to produce methane from labile carbon substrates depending on climate-driven modes of solute transport. Future changes in precipitation may therefore play a central role in determining the source strength of peatlands in the global methane cycle.
Bibliographical noteFunding Information:
This work was supported by awards from the National Science Foundation (9007161, 965292, 96515429, and 0628647), U.S. Department of Energy, National Aeronautics and Space Administration, and Minnesota Department of Natural Resources. We thank Michael Gracz for technical assistance, the Minnesota DNR allowing the usage of their Hatcheries facility in Waskish, MN, as a base for field operations, and Lee Andrew and Brainerd Helicopter Company for helicopter access to our field sites. We also thank Nigel Roulet, Tim Moore, Keith Lucey, and an anonymous reviewer for their critical review of the manuscript. Data used in this paper are available from cited sources or can be acquired by contacting the corresponding author. The corresponding author for this paper is Paul H. Glaser at email@example.com.
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- carbon cycling
- climatic change
- methane production