Nutrient Release From Permafrost Thaw Enhances CH₄ Emissions From Arctic Tundra Wetlands

High-latitude climate change has impacted vegetation productivity, composition, and distribution across tundra ecosystems. Over the past few decades in northern Alaska, emergent macrophytes have increased in cover and density, coincident with increased air and water temperature, active layer depth, and nutrient availability. Unraveling the covarying climate and environmental controls influencing long-term change trajectories is paramount for advancing our predictive understanding of the causes and consequences of warming in permafrost ecosystems. Within a climate-controlled carbon flux monitoring system, we evaluate the impact of elevated nutrient availability associated with degraded permafrost (high-treatment) and maximum field observations (low-treatment), on aquatic macrophyte growth and methane (CH₄) emissions. Nine aquatic Arctophila fulva-dominated tundra monoliths were extracted from tundra ponds near Utqiaġvik, Alaska, and placed in growth chambers that controlled ambient conditions (i.e., light, temperature, and water table), while measuring plant growth (periodically) and CH₄ fluxes (continuously) for 12 weeks. Results indicate that high nutrient treatments similar to that released from permafrost thaw can increase macrophyte biomass and total CH₄ emission by 54 and 64%, respectively. However, low treatments did not respond to fertilization. We estimate that permafrost thaw in tundra wetlands near Utqiaġvik have the potential to enhance regional CH₄ efflux by 30%. This study demonstrates the sensitivity of arctic tundra wetland biogeochemistry to nutrient release from permafrost thaw and suggests the decadal-scale expansion of A. fulva-dominant aquatic plant communities, and increased CH₄ emissions in the region were likely in response to thawing permafrost, potentially representing a novel case study of the permafrost carbon feedback to warming.