Temporal Variation of Ecosystem Scale Methane Emission From a Boreal Fen in Relation to Temperature, Water Table Position, and Carbon Dioxide Fluxes

Abstract

We have analyzed decade‐long methane flux data set from a boreal fen, Siikaneva, together with data on environmental parameters and carbon dioxide exchange. The methane flux showed seasonal cycle but no systematic diel cycle. The highest fluxes were observed in July–August with average value of 73 nmol m−2 s−1. Wintertime fluxes were small but positive, with January–March average of 6.7 nmol m−2 s−1. Daily average methane emission correlated best with peat temperatures at 20–35 cm depths. The second highest correlation was with gross primary production (GPP). The best correspondence between emission algorithm and measured fluxes was found for a variable‐slope generalized linear model (r2 = 0.89) with peat temperature at 35 cm depth and GPP as explanatory variables, slopes varying between years. The homogeneity of slope approach indicated that seasonal variation explained 79% of the sum of squares variation of daily average methane emission, the interannual variation in explanatory factors 7.0%, functional change 5.3%, and random variation 9.1%. Significant correlation between interannual variability of growing season methane emission and that of GPP indicates that on interannual time scales GPP controls methane emission variability, crucially for development of process‐based methane emission models. Annual methane emission ranged from 6.0 to 14 gC m−2 and was 2.7 ± 0.4% of annual GPP. Over 10‐year period methane emission was 18% of net ecosystem exchange as carbon. The weak relation of methane emission to water table position indicates that space‐to‐time analogy, used to extrapolate spatial chamber data in time, may not be applicable in seasonal time scales.

Small spatial but large sporadic variability in methane emission measured from a patterned boreal bog

“…Moreover, Korrensalo (2017) showed that biomass production rates on the same bog site are similar among the plant community types, except on bare peat surfaces that produce very little biomass. This can also partly explain our result, as methane emission has a positive correlation with primary production (Whiting and Chanton, 1993;Rinne et al, 2017).…”

Multi-year methane ebullition measurements from water and bare peat surfaces of a patterned boreal bog

“…Similar to chamber and EC measurements (Rinne et al, , 2018Jackowicz-Krczyński et al, 2010;Turetsky et al, 2014;Mikhaylov et al, 2015), direct ebullition studies have connected the rate of methane emission to peat temperature (Strack et al, 2005) related to increasing microbial activity (Conrad et al, 1997). It is noteworthy that the incoming energy flux has been shown to primarily control the methane production and ebullition in shallow subarctic lakes (Wik et al, 2014) that could be contrasted to peatland pools.…”

“…Alternatively, the eddy covariance (EC) technique is used to estimate the integrated ecosystem-scale methane flux (e.g. Brown et al, 2014;Rinne et al, 2018) but is unable to differentiate the emission pathways.…”

Methane Efflux Measured by Eddy Covariance in Alaskan Upland Tundra Undergoing Permafrost Degradation

“…However, CH 4 emissions have less well understood hysteresis dynamics. Lagged emissions have been shown over the growing season with respect to water table depths (Moore & Roulet, ), gross primary productivity (Rinne et al, ), and annually with soil temperatures (Zona et al, ). At Ivotuk, a dry, upland tundra site similar to EML, strong seasonal hysteresis was attributed to stronger spring CH 4 oxidation, while later in the season more CH 4 is stored in the deeper active layer (Zona et al, ).…”