Relationships Between Methane and Carbon Dioxide Fluxes in a Temperate Cattail‐Dominated Freshwater Wetland

Abstract

Wetlands are the most important natural source of methane (CH4) to the atmosphere, and there is still considerable uncertainty of CH4 flux and net carbon budgets of wetlands. This uncertainty is due in part to the complex role of wetland vegetation in controlling methane production, oxidation and transport, which challenge the modeling and forecast of CH4 fluxes. We combined CH4 and carbon dioxide (CO2) fluxes measured by the eddy covariance technique during two consecutive growing seasons with continuous measurements of water levels and water temperature in a Typha angustifolia L patch of a temperate wetland. We seek to evaluate the role of vegetation in CH4 flux processes. To this end, we determined the relationship between CH4 and CO2 fluxes, directly and indirectly linked to plant activity. Our results indicated significant but opposing relationships between CH4 and CO2 fluxes during the daytime and nighttime. Consequently, when analyzed on a diel timescale, this relationship was not significant. Both CH4 and CO2 fluxes were highly dependent on environmental drivers, and thus, the correlations observed at both the nighttime and daytime were likely the result of a shared response to environmental variables. Focusing on water temperature (the most commonly observed environmental variable in wetlands) and water level (the most commonly controlled one) as operational control variables for wetlands, we identified “hot” condition combinations when CH4 flux and net ecosystem CO2 uptake are maximized at half hourly and diel scales.

Lagged Wetland CH4 Flux Response in a Historically Wet Year

“…The lag time between plant C assimilation and soil CO 2 efflux (i.e., microbial decomposition & root respiration) takes less than one day for grasses and up to 5 days for mature trees (Kuzyakov & Gavrichkova, 2010). Due to plant metabolism, one would expect, in anoxic soil conditions, a similar lagged influence of GPP on soil FCH 4 , which has been detected and discussed in some studies (Bridgham et al, 2013;Mitra et al, 2020;Updegraff et al, 2001) but not others (Villa et al, 2019) or may disappear after temperature-normalization (Chen et al, 2020;Rinne et al, 2018). Methane emission can be stimulated by plant shoot clipping (which results in the growth of new roots) in as few as three days, although the short duration of mesocosm experiments limits measurement of maximum total lag time (Rietl et al, 2017).…”

Practical Guide to Measuring Wetland Carbon Pools and Fluxes

“…EC measurements are well-suited for capturing the complex processes, emergent properties, and spatial heterogeneity inherent in wetland ecosystems. For example, the simultaneous measurements of CO 2 , water vapor, and CH 4 help determine how recent photosynthate may prime soil microbial processes, how xylem transport may facilitate CH 4 losses through vegetation, or the role that water stratification plays in the convective overturning or suppression of gas transfer (Poindexter et al 2016 ; Sturtevant et al 2016 ; Villa et al 2019b ; Ueyama et al 2023 ).…”

Biophysical Controls of Ecosystem‐Scale Methane Fluxes From a Subtropical Estuarine Mangrove: Multiscale, Nonlinearity, Asynchrony and Causality

“…Their effects on F CH4 can be maximized over day-night cycles given their significant variability at the diel scale (Figure 2). Strong connections between NEE and F CH4 have been found in wetlands at the hourly (Villa et al, 2019) and diel (Pypker et al, 2013) scales in part because of the temperature-driven diel patterns of F CH4 , GPP and R eco in some wetlands. Yet, the connection may become weak at the annual scale (Knox et al, 2019).…”