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Ebullition dominates methane fluxes from the water surface across different ecohydrological patches in a temperate freshwater marsh at the end of the growing season
Citation:
Villa, J., Y. Ju, T. Yazbeck, S. Waldo, K. Wrighton, AND G. Bohrer. Ebullition dominates methane fluxes from the water surface across different ecohydrological patches in a temperate freshwater marsh at the end of the growing season. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 767:144498, (2021). https://doi.org/10.1016/j.scitotenv.2020.144498
Impact/Purpose:
Methane is a potent greenhouse gas contributing to the warming of the earths atmosphere. Wetlands are the largest natural source of methane to the atmosphere, but estimating wetland emissions is difficult due to strong spatial variation in emission rates. Here we assess spatial variation in wetland methane emissions by making measurement in distinct habitat patches within an interconnected wetland system. We found that emission rates vary by an order of magnitude across habitat patches, highlighting the difficulty in estimating methane emissions at the system scale. This finding has important implications for our understanding of the global methane budget. When all known methane emissions are added up, they exceed the amount of methane accumulating in the atmosphere, suggesting that we are overestimating some sources. This work suggests that extreme spatial variation in wetland emission rates cause a risk of under or overestimating emissions and highlights the need to improve measurement methodologies. This work will be of interest to wetland ecologist or those involved in national greenhouse gas inventories.
Description:
Measurements of the spatial heterogeneity of methane fluxes in wetlands are critical to better understand and predict methane emissions at the ecosystem scale. However, the within-wetland spatial heterogeneity of fluxes is rarely assessed. Here, we use a spatially balanced rapid chamber-based survey of methane at different ecohydrological patches within a temperate freshwater marsh. We measured fluxes exclusively from the water surface without including vegetation. We further used the data from chamber measurements to partition diffusive and ebullitive fluxes. Three ecohydrological patches were distinguishable in the marsh, defined by the type and presence/absence of vegetation. These patches were emergent vegetation, floating-leaved, and open water. Net methane fluxes from the water surface (diffusion plus ebullition) in emergent vegetation patches were larger than in the floating-leaved vegetation and open water patches (p < 0.05). Diffusive fluxes, representing a sizable smaller fraction of net fluxes, were larger in vegetated than in unvegetated patches (p < 0.05), while ebullitive fluxes mirrored the magnitude and differences observed in the net fluxes. Moreover, pooled net and ebullitive fluxes across patches (but not diffusive fluxes) were negatively correlated with water levels, the primary variable affecting patch distribution. Altogether, our results indicate that the differences among ecohydrological patches are driven by ebullition, ultimately highlighting challenges faced by scientists and practitioners in the field and modelers seeking to improve the predictability and resolution of wetland biogeochemical models.
URLs/Downloads:
DOI: Ebullition dominates methane fluxes from the water surface across different ecohydrological patches in a temperate freshwater marsh at the end of the growing season
https://pubmed.ncbi.nlm.nih.gov/33421641/