At a Glance
Methane (CH4) is the second most important anthropogenic climate forcer after carbon dioxide. Determining the importance and mechanisms of different anthropogenic and natural methane sources and sinks across temporal and spatial scales remains a fundamental challenge for the scientific community. Wetlands are dominant but highly variable sources of methane and are predicted to play a critical role in carbon-climate feedbacks. Methane emissions from these areas are shaped by a complex and poorly understood interplay of microbial, hydrological, and plant-associated processes that vary in time and space.
The CMI Wetland Project aims to identify the biological and chemical mechanisms that promote methane emissions from wetlands. The goals are to improve predictions of carbon-climate feedbacks and strategies of methane mitigation. A better understanding of the factors responsible for the greatest methane emissions from wetlands is crucial to bp’s actions aimed at targeting this powerful greenhouse gas and thus a vital step towards a low-emissions future.
Atmospheric CH4 has risen to levels roughly 150% above preindustrial concentrations due to human activities. These levels continue to rise despite a short period of stabilization between 1999 and 2006. Wetlands are geographically and biogeochemically diverse environments that together constitute the largest and most variable sources of methane to the atmosphere. CMI Wetland Project researchers are investigating the microbial, chemical, and hydrological pathways that regulate methane emissions from diverse wetland soils that vary in biogeochemical composition and hydrologic environment.
Ongoing research builds on prior CMI discoveries that transient oxygenation associated with hydrological variability unlocks a microbial “latch” on wetland carbon flow that ultimately makes mineral-poor, peaty wetlands drastically more methanogenic (Figure 6.1a, Wilmoth et al., 2021). The researchers have pieced together fragments of genetic information from peat microbiomes to recreate microbial genomes. This has allowed the researchers to show that transient oxygenation selects for different keystone microorganisms at multiple steps of the microbial food chain underlying peat carbon conversion into methane (Figure 6.1b, Reji et al., submitted).
To better constrain the effects of hydrologically driven oxygen variability on methane emissions from a greater diversity of wetlands, current work examines wetlands along a fresh to saltwater continuum, including organic-rich peat, mineral-soil marsh, and saltmarsh sediments. Preliminary results indicate that oxygen-rich to poor transitions accelerate methane emissions from peat and marsh soils, but not from saltmarsh sediments. Geochemical variables such as pH, mineral composition, and organic carbon content are significantly different between the peat and marsh soils. This suggests that distinct microbial mechanisms underlie the observed methane emission patterns. Researchers are in the process of disentangling these biological and geochemical mechanisms. They have also started to examine the efficacy of chemical amendments like biochar in reducing wetland methane emissions.
The CMI Wetland Project has identified the influence of environmental conditions (e.g., O2 , soil saturation, water table, salinity) and soil molecular form on microbial biodiversity as keys to better constrain and mitigate wetland methane emissions. The researchers urge the adoption of strategies to limit greenhouse gas emissions from natural and constructed wetlands, as part of land-based climate solution initiatives in freshwater wetlands (e.g., Wilmoth et al., 2021; Calabrese et al., 2021). Ongoing collaborations with the Bourg, Stone, and Porporato groups (Yang et al., 2021) address how soil minerology and biophysics can be manipulated to support soils-based carbon mitigation efforts.
Calabrese, S., A. Garcia, J.L. Wilmoth, X. Zhang, and A. Porporato, 2021. Critical inundation level for methane emissions from wetlands. Environmental Research Letters 16:044038. (https://doi.org/10.1088/1748-9326/abedea).
Reji, L., and X. Zhang. Genome-resolved metagenomics informs functional ecology of uncultured Acidobacteria in redox oscillated Sphagnum peat. In review, mSystems.
Wilmoth, J., J.K. Schaefer, D. Schlesinger, S. Roth, P. Hatcher, J. Shoemaker, and X. Zhang, 2021. The role of oxygen in stimulating methane production by wetlands. Global Change Biology 00:1–17. (https://doi.org/10.1111/gcb.15831).
Yang, J.Q., X. Zhang, I. Bourg, and H. Stone, 2021. 4D imaging reveals mechanisms of clay-carbon protection and release. Nature Communications 12:622. (https://doi.org/10.1038/s41467-020-20798-6).