Environmental and biogeochemical drivers of CH4 and N2O flux variability in treatment wetlands

Abstract

Methane (CH₄) and nitrous oxide (N₂O) emissions from wetlands vary spatially, influencing total greenhouse gas (GHG) fluxes. Accurately quantifying these variations is essential for refining CH₄ and N₂O budgets and developing effective mitigation strategies. This study applies the closed chamber method to assess CH₄ and N₂O flux variability over five years in treatment wetlands designed to reduce agricultural diffuse pollution, focusing on key environmental and biogeochemical drivers at 12 sampling points. Hotspots, identified as sampling points where high-emission events (hot moments) contributed disproportionately, exceeding 8.33 % of total emissions, were determined from the mean plus two-standard-deviation threshold. Median (interquartile range) CH₄ emissions were 115.86 (16.1–1191.31) μg CH₄-C m⁻² h⁻¹ in hotspots and 109.15 (27.49–722.62) μg CH₄-C m⁻² h⁻¹ in non-hotspots. Similarly, median N₂O emissions were 75.33 (29.71–187.85) μg N₂O-N m⁻² h⁻¹ in hotspots, compared to 15.41 (5.87–38.01) μg N₂O-N m⁻² h⁻¹ in non-hotspots. Statistical analysis identified water level as the key predictor of N₂O flux differences, with lower water levels driving higher emissions. CH₄ fluxes were influenced by multiple interacting factors, including dissolved oxygen, oxidation-reduction potential, conductivity, and water level, with the highest emissions under more reducing conditions. Seasonal trends revealed higher CH₄ and N₂O fluxes during the growing season, coinciding with higher temperatures and reduced flow rates. Our findings highlight the critical role of water level regulation, flow rate control, and oxygenation strategies in reducing CH₄ and N₂O emissions. These insights contribute to optimizing wetland design and management for water treatment efficiency and climate mitigation.