Methane emissions from high latitude peatlands - bridging the abyss between environmental factors and ecosystem scale methane formation and emission

Created 2022-06-07 05:12:44 and last modified 2022-06-07 06:23:46 CET
Began in 2020

This research aims to take advantage of the good existing understanding of the basic biogeochemistry of methane, in order to link direct ecosystem scale Eddy covariance measurements of methane fluxes to the main drivers of methane formation and oxidation.

Background / theoretical reference context

Methane is the second most important biogenic greenhouse gas after carbon dioxide (Boucher et al., 2009; Tiwari et al., 2020), but it is more than 20 times as potent as carbon dioxide on a molecule-to-molecule basis in terms of warming potential (Shindell et al., 2013). A recent study reported a growth rate of 18.2 (17.3-19) Tg CH₄ / yr in atmospheric methane concentrations for the period 2008-2017 (Saunois et al., 2020), which makes methane an attractive target for climate change mitigation policies. Wetlands in general and peatlands in particular are the most important natural source of atmospheric methane. High latitude peatlands are particularly of interest since they are undergoing the most substantial changing climate, which could affect significantly methane emissions from these ecosystems (Tiwari et al., 2020). Thus, it is of paramount importance to understand properly how high latitude peatlands will behave, by linking actual measured emissions, to the fundamental drivers of methane formation and oxidation.

Scientific problems and relevance

Several studies have proven water table depth and temperature to be good proxies for methane production and oxidation (Abdalla et al., 2016; Moore and Knowles, 1989). In fact, the microorganisms responsible for methane production (methanogens) require anoxic conditions made possible by the saturated and wet part of peatlands. At higher temperatures, methanotrophs are not able to compensate for the increased production of methane, leading to higher emissions (van Winden et al., 2012). Although temperature and water table depth alone can explain a good part of methane fluxes, they are not the fundamental drivers, but instead, they act as regulators. Recent studies also showed the importance of substrate availability over environmental drivers on methane production (Mitra et al., 2020). It would be therefore important to consider the main drivers involved in methane production and oxidation, i.e. the ratio of methanogens and methanotrophs, as well as substrate supply (GPP and plant phenology) in the attempt of a more comprehensive description of methane fluxes.

Study sites

The mires, subject of this PhD project are located in the Kulbäcksliden area (near the municipality of Vindeln, county of Västerbotten in northern Sweden), all four within a distance of less than 3 km. They are all more or less nutrient poor, as they do not receive water and nutrients from any major water sources. Mean annual precipitation and temperature over 30 years (1961-1990) are 523 mm and +1.2 °C, respectively (Alexandersson et al., 1991).