Wetland Heterogeneity Determines Methane Emissions: A Pan-Arctic Synthesis.

Methane (CH4) emissions from pan-Arctic wetlands provide a potential positive feedback to global warming. However, the differences in CH4 emissions across wetland types in these regions have not been well understood. We synthesized approximately 9000 static chamber CH4 measurements during the growing season from 83 sites across pan-Arctic regions. We highlighted spatial variations of CH4 emissions corresponding to environmental heterogeneity across wetland types. CH4 emission is the highest in fens, followed by marshes, bogs, and the lowest in swamps. This gradient is controlled by the water table, soil temperature, and dominant plant functional types and their interactions. The water table position for maximum CH4 emission is below, close to, and above the ground surface in bogs, marshes/fens, and swamps, respectively. The temperature sensitivity (Q10) of CH4 emissions varied among different wetland types, ranging from the lowest in swamps to the highest in fens. The interactive impact of temperature and the water table positions on CH4 emissions are regulated with dominant plant functional types. CH4 emissions from wetlands dominated by vascular plants rely more on species composition than that dominated by non-vascular plants. Wetlands with greater abundance of graminoids (e.g., fens) have higher CH4 emissions than tree-dominated wetlands (e.g., swamps). This synthesis emphasizes the role of wetland heterogeneity in determining the strength of CH4 emissions.