Soil Nitrogen Dynamics Impact Carbon Exchange Processes in a High Arctic Wetland

Abstract Increased soil nutrient availability, and associated increases in vegetation productivity, could create a negative feedback between Arctic ecosystems and the climate system, thereby reducing the contribution of Arctic ecosystems to future climate change. To predict whether this feedback will develop, it is important to understand the environmental controls over nutrient cycling in High Arctic ecosystems and their impact on carbon cycling processes. This study, conducted at the Cape Bounty Arctic Watershed Observatory, Melville Island, Nunavut, examined the environmental controls over soil nitrogen availability in a High Arctic wet sedge meadow and how they influenced carbon dioxide exchange processes from 2016-2018. Moisture variability across a seemingly homogenous wet sedge meadow allowed us to investigate nutrient availability and carbon dioxide exchange across naturally occurring moisture gradients over three growing seasons. The nature of the relationships (i.e., trends) between variables was consistent over the three years, but their magnitudes varied depending on climate conditions. Soil nitrogen availability, particularly ammonium, was higher in warmer years and wetter conditions and correlated positively with gross primary production (R 2 = 0.97) and net carbon dioxide uptake (R 2 = 0.88). Drier areas within the wetland had more nitrate availability, and this correlated negatively with net carbon dioxide exchange. Projections of a warmer, wetter Arctic and increased nutrient availability due to higher soil organic matter turnover suggest that northern wetlands will remain strong carbon dioxide sinks, or become stronger sinks, contributing to a negative feedback on the climate system.