Greenhouse carbon balance of wetlands: methane emission versus carbon sequestration

Abstract

Carbon fixation under wetland anaerobic soil conditions provides unique conditions for long‐term storage of carbon into histosols. However, this carbon sequestration process is intimately linked to methane emission from wetlands. The potential contribution of this emitted methane to the greenhouse effect can be mitigated by the removal of atmospheric CO2 and storage into peat. The balance of CH4 and CO2 exchange can provide an index of a wetland's greenhouse gas (carbon) contribution to the atmosphere. Here, we relate the atmospheric global warming potential of methane (GWPM) with annual methane emission/carbon dioxide exchange ratio of wetlands ranging from the boreal zone to the near‐subtropics. This relationship permits one to determine the greenhouse carbon balance of wetlands by their contribution to or attenuation of the greenhouse effect via CH4 emission or CO2 sink, respectively. We report annual measurements of the relationship between methane emission and net carbon fixation in three wetland ecosystems. The ratio of methane released to annual net carbon fixed varies from 0.05 to 0.20 on a molar basis. Although these wetlands function as a sink for CO2, the 21.8‐fold greater infrared absorptivity of CH4 relative to CO2(GWPM) over a relatively short time horizon (20 years) would indicate that the release of methane still contributes to the overall greenhouse effect. As GWPM decreases over longer time horizons (100 years), our analyses suggest that the subtropical and temperate wetlands attenuate global warming, and northern wetlands may be perched on the “greenhouse compensation” point. Considering a 500‐year time horizon, these wetlands can be regarded as sinks for greenhouse gas warming potential, and thus attenuate the greenhouse warming of the atmosphere.

Relationships Between Salinity and Short-Term Soil Carbon Accumulation Rates from Marsh Types Across a Landscape in the Mississippi River Delta

“…Balancing the greenhouse gas emissions from each of these four marsh types with the short-term carbon accumulation rates may provide a comprehensive understanding of the role of these marshes in overall carbon sequestration (Poffenbarger et al 2011;Holm et al 2016;Krauss et al 2016). For example, fresh marshes may accumulate a large amount of carbon, but they produce methane gas during anaeraboic metabolism, which has a global warming potential that is 25 times greater than carbon dioxide (Whiting and Chanton 2001).…”

Plant-mediated methane and nitrous oxide fluxes from a carex meadow in Poyang Lake during drawdown periods

“…The same results were observed in a subarctic peatland in Northern Sweden (Bäckstrand et al 2010). Moreover, if the global warming potential (GWP) of CH 4 and N 2 O is taken into account, many other wetlands could turn into sources of atmospheric radiative forcing (Whiting and Chanton 2001;Friborg et al 2003). Hence, it is necessary to integrate both CH 4 and N 2 O into assessments for the net greenhouse gas (GHGs) effect from wetlands.…”

“…CH 4 and N 2 O have 28 and 265 times larger global warming potentials (GWP) than CO 2 over a 100-year timescale, respectively (IPCC 2013). When the GWP of CH 4 and N 2 O are taken into account, many studies have suggested the wetland C sink could be largely offset, and potentially turn into sources of atmospheric radiative forcing (Whiting and Chanton 2001;Friborg et al 2003;Ding et al 2013). In the Carex meadow, soil CO 2 emission dominated the GHG emissions (Table 2).…”

Changes in peat chemistry associated with permafrost thaw increase greenhouse gas production

“…The fate of this carbon in a warming climate-i.e., the responses of net carbon balance and CH 4 emissions-is important in predicting climate feedbacks of permafrost thaw. Although northern peatlands are currently a net carbon sink, and have been since the end of the last glaciation, they are a net source of CH 4 (4,5), emitting 0.046-0.09 Pg of carbon as CH 4 per year (4,6,7). Due to CH 4 's disproportionate global warming potential (33× CO 2 for 1 kg CH 4 vs. 1 kg CO 2 at a 100-y timescale) (8), this is equivalent to 6-12% of annual fossil fuel emissions of CO 2 (8.7 Pg of C) (9).…”