How much of the carbon breakdown in waterlogged peatlands can scientists explain?

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Peatland soils hold globally significant stores of carbon, so understanding how carbon cycles through these ecosystems has important implications for global climate change.

Over one growing season, researchers measured acetate-based (aceticlastic) and autotrophic methane production, sulfate reduction, denitrification, and iron reduction in a bog, an intermediate fen, and a rich fen in Michigan’s Upper Peninsula. The study used 3-day anaerobic incubations of slurried peat. In these incubations, denitrification and iron reduction were minor components of anaerobic carbon mineralization—the breakdown of organic carbon without oxygen.

Experiments using 14C-labeled methanogenic substrates showed that methane production in these peatlands mainly followed the aceticlastic pathway. The exception was early in the growing season in the more rain-fed, or ombrotrophic, peatlands, where the autotrophic pathway was dominant or codominant.

Overall, methane production accounted for 3–70% of anaerobic carbon mineralization. Sulfate reduction accounted for 0–26%, suggesting rapid turnover of a very small sulfate pool.

A large share of anaerobic carbon mineralization, 29–85%, was not explained by any measured process. This unexplained share could have resulted from fermentation or possibly from organic molecules, such as humic acids, being used as alternative electron acceptors.