External carbon addition increases nitrate removal and decreases nitrous oxide emission in a restored wetland

To improve the ecosystem services of wetlands in response to global climate change, wetland restoration projects have become prevalent worldwide. Restored wetlands have the potential to remove external nitrogen through denitrification, but incomplete denitrification may increase nitrous oxide (N₂O) release. In order to comprehensively understand nitrogen removal and N₂O emission processes in restored wetlands, we conducted carbon (anhydrous sodium acetate) and nitrogen (sodium nitrate) addition experiments in the Fengxian coastal wetland site. These experiments explored the roles of external nitrogen, carbon sources, and wetland plants in nitrogen removal and N₂O emission. With the addition of nitrogen, the removal of external nitrogen was significant at the restored wetland site, but led to increasing N₂O release. However, by adding carbon sources, the restored wetland could not only enhance nitrogen removal efficiency through denitrification, but also significantly reduce N₂O emission. Our results demonstrate that carbon availability could improve the ecological functions of coastal restored wetlands by improving water quality and mitigating greenhouse gas emissions.