A synthesis of methane emissions from 71 northern, temperate, and subtropical wetlands

Abstract

Wetlands are the largest natural source of atmospheric methane. Here, we assess controls on methane flux using a database of approximately 19 000 instantaneous measurements from 71 wetland sites located across subtropical, temperate, and northern high latitude regions. Our analyses confirm general controls on wetland methane emissions from soil temperature, water table, and vegetation, but also show that these relationships are modified depending on wetland type (bog, fen, or swamp), region (subarctic to temperate), and disturbance. Fen methane flux was more sensitive to vegetation and less sensitive to temperature than bog or swamp fluxes. The optimal water table for methane flux was consistently below the peat surface in bogs, close to the peat surface in poor fens, and above the peat surface in rich fens. However, the largest flux in bogs occurred when dry 30-day averaged antecedent conditions were followed by wet conditions, while in fens and swamps, the largest flux occurred when both 30-day averaged antecedent and current conditions were wet. Drained wetlands exhibited distinct characteristics, e.g. the absence of large flux following wet and warm conditions, suggesting that the same functional relationships between methane flux and environmental conditions cannot be used across pristine and disturbed wetlands. Together, our results suggest that water table and temperature are dominant controls on methane flux in pristine bogs and swamps, while other processes, such as vascular transport in pristine fens, have the potential to partially override the effect of these controls in other wetland types. Because wetland types vary in methane emissions and have distinct controls, these ecosystems need to be considered separately to yield reliable estimates of global wetland methane release.

Environmental correlates of peatland carbon fluxes in a thawing landscape: do transitional thaw stages matter?

“…Our correlations support previous findings from various wetland types (as reviewed in Lai, 2009;Olefeldt et al, 2013;Turetsky et al, 2014). The multiple regression analysis of lumped data across Stordalen also showed similar trends to other temperate, boreal or arctic peatlands.…”

Does <i>Juncus effusus</i> enhance methane emissions from grazed pastures on peat?

“…As would be expected, the highest emission rates were observed at Torsager after flooding, with rates equivalent to those reported from permanently flooded peatlands (Günther et al, 2013;Kim et al, 1999;Turetsky et al, 2014). Several authors have suggested that CH 4 emissions are insignificant when the GWL is below a certain threshold of 20 to 30 cm below the soil surface (Audet et al, 2013;Koebsch et al, 2013;Shannon and White, 1994).…”

Root oxygen loss from Raphia taedigera palms mediates greenhouse gas emissions in lowland neotropical peatlands

“…Variance accounted by the models is reported as the adjusted r 2 when regression relationship was significant. Relevant statistics are shown in text Turetsky et al 2014b). Furthermore, the lower solubility of oxygen as temperature increased (Wilhelm et al 1977) and cessation of radial oxygen loss from the roots following the clearing of the R. taedigera forest exacerbated anaerobic conditions (Fig.…”