Nongrowing season methane emissions–a significant component of annual emissions across northern ecosystems

Abstract

Wetlands are the single largest natural source of atmospheric methane (CH ), a greenhouse gas, and occur extensively in the northern hemisphere. Large discrepancies remain between "bottom-up" and "top-down" estimates of northern CH emissions. To explore whether these discrepancies are due to poor representation of nongrowing season CH emissions, we synthesized nongrowing season and annual CH flux measurements from temperate, boreal, and tundra wetlands and uplands. Median nongrowing season wetland emissions ranged from 0.9 g/m in bogs to 5.2 g/m in marshes and were dependent on moisture, vegetation, and permafrost. Annual wetland emissions ranged from 0.9 g m year in tundra bogs to 78 g m year in temperate marshes. Uplands varied from CH sinks to CH sources with a median annual flux of 0.0 ± 0.2 g m year . The measured fraction of annual CH emissions during the nongrowing season (observed: 13% to 47%) was significantly larger than that was predicted by two process-based model ensembles, especially between 40° and 60°N (modeled: 4% to 17%). Constraining the model ensembles with the measured nongrowing fraction increased total nongrowing season and annual CH emissions. Using this constraint, the modeled nongrowing season wetland CH flux from >40° north was 6.1 ± 1.5 Tg/year, three times greater than the nongrowing season emissions of the unconstrained model ensemble. The annual wetland CH flux was 37 ± 7 Tg/year from the data-constrained model ensemble, 25% larger than the unconstrained ensemble. Considering nongrowing season processes is critical for accurately estimating CH emissions from high-latitude ecosystems, and necessary for constraining the role of wetland emissions in a warming climate.

Tundra landscape heterogeneity, not interannual variability, controls the decadal regional carbon balance in the Western Russian Arctic

“…In this study, the cold season fluxes resulted in differences in modeled NEE among land cover types (Figure a) but contributed little to the interannual variability of modeled NEE (Figure b). Modeled nongrowing season CH 4 flux measurements were also important for variability among land cover types in this study (Figure c), but not as important for interannual variability (Figure d), similar to recent findings across many sites (Treat, Bloom, & Marushchak, ).…”

Seasonal Controls of CO2 and CH4 Dynamics in a Temporarily Flooded Subtropical Wetland

“…Fluxes of CH 4 persisted during the dry season, although they were higher during the wet season (Table and Figure ). Given the observed magnitude of nongrowing season CH 4 fluxes, our results support the emerging view that nearly continuous observations may be required to accurately estimate annual CH 4 budgets from temporarily flooded subtropical wetlands (Treat et al, ).…”

“…We also calculated cumulative fluxes of each scalar during the dry and wet seasons to investigate whether the dominance of climatic and plant‐mediated factors controlling CH 4 fluxes from wetlands vary between the growing and the nongrowing seasons. A recent study showed that in high‐latitude wetlands, modeled CH 4 emissions during the nongrowing season tend to be smaller than observations, suggesting that factors driving CH 4 emissions and likely other GHGs could differ between seasons (Treat et al, ). In this study, measurements were done from 1 July 2013 to 31 December 2015.…”

Advances in the Eddy Covariance Approach to CH4 Monitoring Over Two and a Half Decades

“…While high‐latitude interannual flux measurements remain rare, in recent years towers have made considerable efforts to run continuously, bolstering our knowledge base on dormant season measurements (Figure c). It is increasingly clear that CH 4 fluxes in the dormant season comprise a large percentage of total ecosystem fluxes (Morin, Bohrer, Naor‐Azrieli, et al, ; Taylor et al, ; Zona et al, ) and that nongrowing season fluxes must be included when estimating regional CH 4 fluxes (Treat et al, ). One study in the arctic determined that dormant season fluxes were the dominant source to the annual budget (Zona et al, ).…”