Methane trapping and release in restored and unrestored peatlands.

Unique biochemical and environmental conditions prevailing in natural peat deposits makepeatlands one of the largest natural emitters of methane (CH4) to the atmosphere. Methanecan be released through ebullition, diffusion and plant tissues. Under anaerobic conditions inthe subsurface, a portion of CH4 undergoes oxidation by methanotrophs. Considerableamounts of CH4 become trapped under the peat surface in dissolved or gaseous phase.Biogenic free-phase gas (FPG) in peatlands accounts for up to 1/5 of the total peat volumeand contains up to 50% of CH4. Horticulture peat extraction targets peat of certain type (e.g., low-decomposed Sphagnumpeat) leaving behind a part of the peat deposit that is less profitable for the industry. Theseseverely disturbed ecosystems are stripped of vegetation and dried through installed ditched,while the extracted peat is compacted by heavy machinery. During extraction, FPG escapes tothe atmosphere, but how much FPG is released and how much remains within the peat matrixduring and post-extraction is unknown. Does the subsurface CH4 pool recover by itself,which would indicate returning of the ecosystem to the natural carbon balance, or isrestoration necessary to promote this process by returning peatland vegetation andhydrological conditions? Ideally, to answer these questions, the amount of FPG should be assessed before peatextraction to establish an individual baseline for each site. In practice, these dataare very difficult to obtain. However, our site is located at a horticulture peatlandcomplex where currently extracted, unrestored, natural, and restored sites of differentage of restoration are located right next to each other. We can therefore assumethat differences in CH4 dynamics across these sites represent changes over theextraction and restoration process. We used a relatively non-invasive method ofground-penetrating radar with a 100 and 200 MHz antenna to assess the FPG content, CS616probes to measure changes in volumetric water content that indicate gas volume overtime and potentially its movement and release, and Los Gatos Research portablegas analyzer with a chamber to measure diffusive fluxes and monitor ebullitionevents. Environmental conditions and meteorological data were also recorded toinvestigate factors that may influence FPG dynamics. All the data were collected inthe growing seasons of 2013, 2016, and 2017 capturing very dry to extremely wetperiods. Monthly GPR surveys at each site show changes in FPG on a short time scale. Weobserved ebullition and large diffusive fluxes at flooded parts of the restored sites, and lowerCH4 fluxes at unrestored and natural site. Zones of potentially continued CH4 productionand/or trapping during peat extraction have been detected at the unrestored sites. Thepresence of FPG at a newly restored site may be a result of gas trapping under peat layers ofincreased post-extraction density. Obtained results can be applicable in improving greenhouse gas emission inventories andfuture decision-making in peatland management. Simplified methods could be utilized by theindustry for monitoring extracted and restored sites. [ABSTRACT FROM AUTHOR]