Soil moisture inputs from enhanced snowfall impact nitrogen availability and the greenhouse gas balance of High Arctic mesic tundra

Arctic warming and changing precipitation regimes are altering nutrient availability and processes that control the greenhouse gas balance of high latitude ecosystems. Climate warming is expected to increase Arctic winter precipitation, and models show that Arctic precipitation may become rainfall dominated. Changes to biogeochemical processes as a result of climate change and altered moisture regimes will ultimately determine whether the Arctic will enhance or dampen future climate feedbacks. At the Cape Bounty Arctic Watershed Observatory, a full factorial International Tundra Experiment site was established in 2008, allowing for the investigation of ten years of experimental warming and increased snowfall on nutrient availability and greenhouse gas release in this mesic heath tundra across two growing seasons (2017 and 2018). Ambient snowfall conditions had deeper thaw depths than those under enhanced snow conditions, and differences in thaw depth across experimental treatments decreased as the growing season progressed, driven by rainfall. Seasonal and interannual variability in nitrogen availability, carbon dioxide release, and nitrous oxide fluxes were driven by elevated late season rainfall in 2018. While experimental warming decreased soil moisture and ammonium availability and increased CO2 release, these effects were enhanced under wetter conditions. Coupled interactions of enhanced snow and experimental warming also increased nitrate availability, and this corresponded with increased N2O release. Together, results from this study suggest that the greenhouse gas balance of High Arctic environments is closely tied to the interaction between soil moisture and nitrogen availability, which will be moderated by future shifts and interactions between climate variability and ecological responses to permafrost thaw.