Dezhao Gan^1,2,3 & Lei Ma^1,2,3,*

¹ College of Atmospheric Sciences, Lanzhou University, No. 222 Tian-shui South Road, Cheng-guan District, Lanzhou 730000, P.R. China

² Sichuan Zoige Alpine Wetland Ecosystem National Observation and Research Station, Southwest Minzu University, Chengdu 610041, P.R. China

³ Sichuan Zoige Alpine Wetland Ecosystem National Observation and Research Station, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, P.R. China

This paper on methane (CH₄) emissions from peatlands and ditches began in my master's candidate career. In September 2022, I started my master's degree at the College of Atmospheric Sciences, Lanzhou University. Thanks to the careful guidance of my tutor, Dr. Ma, I began to perform the greenhouse gas (GHG) flux measurement in the Zoige alpine peatland, the world’s largest alpine peatlands, including near-pristine peatlands, drained peatlands and rewetted peatlands (i.e., blocking ditches). This is my first time to get close in touch with peatlands, which are globally important ecosystems. Later, I learned through literatures that peatlands are key providers of ecosystem services that enable biodiversity preservation, supply safe drinking water, minimize flood risks, sequester a large amount of carbon (C) and mitigate climate change at regional to global scales^1,2. However, peatlands were widely drained over the globe. We have observed a decrease in the water table depth (WTD) and CH₄ emissions in the terrestrial portion of alpine peatlands due to drainage activities (i.e., for livestock grazing^3,4 and herbage production^5,6). As reported by many previous studies, drainage activities reduce overall CH₄ emissions^7–9; however they are often accompanied by the construction of ditches, which are potential CH₄ emission hotspots^10–12. Unfortunately, existing studies often overlooked the contribution of CH₄ emissions from peatland ditches, especially the offsets of CH₄ emissions from creating ditches in peatlands under different climate zones and land-use types remain unclear.

Our experiment was based on annually paired observations of CH₄ fluxes from near-pristine and drained peatlands, as well as ditch in drained peatland. In addition, environmental variable factors were simultaneously measured to analyze the regulatory mechanisms affecting CH₄ emissions. After conducting one year-round experiment (including non-growing season), we found that near-pristine peatland had the highest CH₄ emissions, at 104 ± 17 kg ha^–1 yr^–1. The annual CH₄ emissions from peatland ditch (31 ± 8 kg C ha^–1 yr^–1) were significantly (p < 0.001) higher than those from drained peatland (5 ± 3 kg C ha^–1 yr^–1), but due to the very small fraction of peatland ditch area (1.8 ± 0.5%), the peatland ditch CH₄ offset was only 0.48 ± 0.24%.

Based on the preliminary results of our experiment mentioned above, we would like to know how much CH₄ emissions from peatland ditches on a global scale? Does it also have a weak offset impact on the decrease in CH₄ emissions caused by drainage in the terrestrial portion of peatlands, as we did in our field experiment? Driven by these motivations, for the first time, we conducted a global meta-analysis and upscaling approaches by compiling annual CH₄ emissions from paired near-pristine peatlands and terrestrial portion of drained peatlands and peatland ditches to address this issue¹³. Results showed that ditches occupy approximately 3.8 (3.1~4.4)% of all drained peatlands. Ditches emit 695 (511~898) kg ha^–1 yr^–1 CH₄ overall, with the highest emissions observed in (sub)tropics. Globally, ditch emissions offset approximately 12 (10~14)% for reductions in CH₄ emissions from peatland drainage. As for the reason why the offset of CH₄ emissions from the ditch at our observation site is lower than the global average, it may be collectively caused by the following reasons: 1) our experimental peatland ditch is frequently dried (influenced mainly by precipitation seasonality), which is not conducive for CH₄ emissions^2,14; 2) the ditch is located in alpine region with high-altitude (~3500 m), and low temperatures can also suppress CH₄ emissions¹² as well as decomposition of the organic-C substrates are suppressed especially in a frozen state¹⁵; 3) the fraction of our experimental ditch is lower than the global average, resulting in a smaller area-weighted contribution. Overall, our findings demonstrate that CH₄ emissions from ditches exhibiting significant spatiotemporal variabilities and highlight that the importance of including ditch CH₄ emissions to robustly quantify emission factors for regional to global peatlands affected by drainage.

We sincerely appreciate the researchers at all stations across the peatlands worldwide for their work under the harsh climate and efforts to make their datasets publicly accessible. Their contributions regarding the establishment of experimental platforms and measurements of the annual CH₄ fluxes from peatlands and peatland ditches, as well as environmental variables made this study possible. Our group has focused mainly on the Tibetan alpine peatlands and performed comprehensive quantifications of drainage and restoration (through blocking drainage ditch) impacts on net ecosystem exchanges of CO₂, CH₄ and N₂O, as well as water storage and discharge in Tibetan alpine peatlands. We hope that our work can provide science-based guidelines for policy-makers and local communities to take actions to conserve pristine peatlands and restore drained peatlands to help preserve biodiversity, regulate hydrology, sequester C and mitigate climate change.

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3.         Ma, L. & Zuo, H. C. Quantifying net carbon fixation by Tibetan alpine ecosystems should consider multiple anthropogenic activities. P. Natl. Acad. Sci. USA. 119, e2115676119 (2022).

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13.       Gan, D. et al. Ditch emissions partially offset global reductions in methane emissions from peatland drainage. Commun. Earth Environ. 5, 640 (2024).

14.       Ma, L. et al. A globally robust relationship between water table decline, subsidence rate, and carbon release from peatlands. Commun. Earth Environ. 3, 254 (2022).

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