Roles of riverine wetlands in diffusive greenhouse gas emissions: Comparing before and after wetland destruction

While wetland construction and restoration are widely employed as nature-based solutions to achieve various eco-environmental goals, their roles in affecting diffusive greenhouse gas (GHG) emissions from the targeted riverine systems remain poorly understood. In this study, we investigated the monthly and diurnal dynamics of diffusive GHG emissions in a headwater river, which initially contained a series of constructed wetlands but were later destroyed. Our findings reveal that the riverine reach with wetlands was a persistent source of diffusive CH₄ and CO₂ emissions, but a periodic sink for N₂O, with mean fluxes of 0.76 mmol m^-2 day^-1, 262.38 mmol m^-2 day^-1, and 5.44 μmol m^-2 day^-1, respectively. The hotspots for CH₄ and CO₂ and sinks for N₂O emissions occur coincidentally in warm months, when vegetative and microbial activities are strong. Once the wetlands were destroyed, we observed reductions in the emission fluxes of N₂O (9.62%), CH₄ (27.23%), and CO₂ (47.73%). Further analysis underscored that the environmental settings as shaped by wetlands foster anaerobic metabolisms, whereas the loss of wetlands reduces nutrient trapping and induces more aerobic conditions, which hinder anaerobic activity and associated GHG production. The comparative nature of this study uniquely illuminates the roles of wetlands in governing diffusive GHG dynamics, providing a valuable, data-driven starting point for a more refined evaluation of their net impact on aquatic GHG budgets.