Nitrous oxide (N₂O) is the third most important anthropogenic greenhouse gas, with atmospheric concentrations increasing from 273 to 336 ppb since 1800, primarily due to the use of agricultural fertilisers. While N₂O fluxes from managed agricultural soils are well studied, recent research has increasingly focused on nutrient-rich Arctic soils. However, most Arctic soils are nutrient-poor, and the mechanisms controlling their typically low N₂O fluxes remain poorly understood. This thesis advances understanding of low N₂O fluxes in a nutrient-poor, highly heterogeneous Arctic peatland based on three years of repeated manual chamber measurements conducted throughout the snow-free season.
A major challenge in quantifying low N₂O fluxes is methodological sensitivity. The performance of a novel portable gas analyser (Aeris MIRA Ultra N₂O/CO₂) was evaluated under both laboratory and field conditions, confirming its suitability for manual chamber measurements in Arctic environments. Practical guidelines were developed for instrument configuration, chamber closure duration, and the critical importance of measuring N₂O fluxes under both light conditions using transparent chambers and dark conditions using opaque chambers.
The results show that the nutrient-poor peatland functions as a continuous, non-negligible but small sink for N₂O during the snow-free season, providing the first in situ evidence of sustained N₂O uptake in Arctic peatlands. In addition, a localised N₂O hot spot was identified, demonstrating that a single site can shift the ecosystem from a net sink to a net source of N₂O. Random forest modelling identified photosynthetically active radiation (PAR) and net ecosystem exchange as the dominant drivers of low N₂O fluxes, with consistent differences between light and dark conditions (Wilcoxon rank-sum test statistic = 0.37, p < 0.001).
This work provides robust methodological guidance, reveals a persistent N₂O sink alongside unexpected emission hot spots, and identifies key environmental drivers of low N₂O fluxes. The findings highlight the necessity of repeated paired light–dark measurements and sufficient spatial replication to detect hot spots in heterogeneous Arctic ecosystems. These results are relevant to Arctic and other nutrient-poor ecosystems worldwide.