Analysis of Methane Emission Characteristics and Environmental Response in Natural Wetlands

Abstract

Wetlands are the most important natural source of methane emissions. Methane emission from wetlands is the result of the synergy of biotic and abiotic factors, and there are three main forms of emission: diffusion, ebullition and plant-mediated. Among them, the plant-mediated methane emission process is an important carbon exchange pathway at the land‒air interface. However, there is a lack of direct observations and side-by-side comparisons of methane emissions from different vegetation types. The environmental response characteristics of methane emissions from different vegetation types are still poorly understood. Based on the FLUXNET-CH4 dataset and the Global Standard Soil Database, we analyzed the environmental response characteristics of methane emissions from wetlands and clarified the important role of wetland plants in methane emission. The analysis results showed that water table depth (WTD) and temperature were the main determinants of wetland methane emissions, but plant-mediated emission processes were the main reason for the high heterogeneity of methane emissions. We categorized wetlands into vascular plant wetlands (VPWs) and moss plant wetlands (MPWs). VPW methane emissions were typically higher and more heterogeneous, whereas MPW methane emissions were lower and less variable. Radiation was the main factor affecting VPW methane emissions, and temperature was the main factor affecting MPW methane emissions. Finally, we constructed a structural equation model of methane emissions from wetlands, and our results suggested that warming increases wetland methane emissions via multiple pathways. These findings highlight the important role of wetland vegetation in methane emissions, which should be seriously considered to help further reduce uncertainty in the assessment of wetland methane emissions.

Keywords: methane, wetlands, vegetation type, environmental response, eddy covariance