Document Type

Article

Publication Date

10-31-2025

Abstract

Redox-active organic matter (RAOM) reduction is an important control on methane production in northern peatlands, but it is unclear how global climate change will affect RAOM reduction. We investigated the effects of water-table levels on RAOM reduction by leveraging a long-term water-table manipulation experiment in an Alaskan fen, which includes Lowered and Raised treatment plots relative to a Control. Common substrate peat was incubated in each plot during one summer of experimental manipulation and another summer of site-wide flooding. During experimental manipulation, common substrate RAOM was more reduced in the Raised plot than the Lowered plot at both 10–20 cm (19.1 ± 0.8 vs. 0.7 ± 0.3 μmol e− g−1 dw peat, p = 0.003) and 30–40 cm (18.0 ± 0.5 vs. 3.6 ± 1.2 μmol e− g−1 dw peat, p = 0.011). During site-wide flooding, differences in common substrate RAOM persisted with greater RAOM reduction in the Raised plot than both Control and Lowered plots (p < 0.05) and greater methane production from Raised plot common substrate. A comparison of the chemical composition of Raised and Control peat during an anaerobic laboratory incubation showed that the compounds removed during microbial processing differed between plots with a higher double bond equivalence to carbon ratio for the Raised plot (0.54 ± 0.13) compared to the Control plot (0.44 ± 0.17). Together, these field and laboratory results suggest that long-term increases in water-table levels can have complex effects on RAOM beyond oxygen availability with the potential to impact methane production from northern peatlands.

Plain Language Summary

Global climate change is expected to affect peatland processes that control the production of greenhouse gases including methane. One key, understudied process is the microbial use of organic molecules as electron acceptors during respiration (called organic matter reduction) in these oxygen-limited environments. To better understand peatland response to global climate change, we studied how long-term differences in water-table levels in an Alaskan fen would affect organic matter reduction. We incubated a well-mixed peat sample in three different water-table manipulation plots and found that organic matter reduction closely followed water-table level, but that legacy water-table levels still had an effect on these organic molecules even when all plots were completely flooded. Plots that had experienced higher water-table levels and higher organic matter reduction also had higher rates of methane production. Our results from in situ porewater chemistry and laboratory incubations of peat suggest that the differences in organic matter reduction observed at the peat surface may be due to a change in how microbes process carbon following long-term water-table changes. Taken together, these findings show that long-term changes to peatland water-table levels can have lasting effects on processes controlling peatland carbon cycling.

Comments

This article was originally published in Journal of Geophysical Research: Biogeosciences, volume 130, in 2025. https://doi.org/10.1029/2025JG009000

Copyright

American Geophysical Union

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