Synthesis of pan-Arctic wetland methane emissions and controls

Natural wetlands as a major methane (CH₄) source, contribute more than 30% of global CH₄ emissions. More than half of the wetlands rich in peat lie in the northern high latitudes. Here, we collected approximately 9000 static chamber CH₄ flux measurements in growing-season from 85 sites reported in 53 studies across pan-Arctic regions. These measurements extended over a wide range of latitudes (sub-Arctic to high-Arctic) and wetlands types (fen, marsh, bog and swamp). In general, CH₄ emissions are higher in low latitudes than high latitudes. In the same latitudes and wetland type, the Eastern Hemisphere shows higher CH₄ emissions than the Western Hemisphere. Our meta-analysis shows that CH₄ emissions are influenced by soil temperature, water table, dominant vegetation types, and disturbances. The optimal water table position for CH₄ emissions is below ground surface in bogs, close to ground surface in marshes and fens, and above ground surface in swamps. CH₄ emissions are more sensitive to temperature in high-Arctic than low-Arctic regions, as indicated by Q₁₀ difference. CH₄ emissions from the wetland dominated by vascular plants are largely dependent on species composition (p < 0.001), in which largest CH₄ emissions occur at sites dominated by graminoids, and the lowest emissions occur at sites dominated by trees. CH₄ emissions from the wetland dominated by nonvascular plants are relatively uniform across plant species (p > 0.05). The sites undergone natural and anthropogenic warming and water table disturbance exhibits distinct characteristics of CH₄ emissions, suggesting that the same functional relationships between CH₄ flux and environmental controls cannot be used across pristine and disturbed wetlands. This study can help to improve our understanding and model simulations of wetland CH₄ emissions in northern high latitudes.