Groundwater discharge as a driver of methane emissions from Arctic lakes.

Lateral CH 4 inputs to Arctic lakes through groundwater discharge could be substantial and constitute an important pathway that links CH 4 production in thawing permafrost to atmospheric emissions via lakes. Yet, groundwater CH 4 inputs and associated drivers are hitherto poorly constrained because their dynamics and spatial variability are largely unknown. Here, we unravel the important role and drivers of groundwater discharge for CH 4 emissions from Arctic lakes. Spatial patterns across lakes suggest groundwater inflows are primarily related to lake depth and wetland cover. Groundwater CH 4 inputs to lakes are higher in summer than in autumn and are influenced by hydrological (groundwater recharge) and biological drivers (CH 4 production). This information on the spatial and temporal patterns on groundwater discharge at high northern latitudes is critical for predicting lake CH 4 emissions in the warming Arctic, as rising temperatures, increasing precipitation, and permafrost thawing may further exacerbate groundwater CH 4 inputs to lakes.