Global warming and eutrophication are fundamental threats to coastal wetlands, but their impacts on nitrogen (N) removal and N₂O emissions remained unresolved. Here, we conducted sediment incubation experiments in coastal mangroves and salt marshes across different climatic zones in China. Denitrification was the major N removal process with potential rates of 0.3-51.4 mg N kg^-1 d^-1, while anammox played a minor role (0-22%). Denitrification increased by 0.2-0.8 and 0.3-4.5 mg N kg^-1 d^-1 for 1℃ warming and 1 mg L^-1 NO₃-N increase, respectively. Subtropical wetlands had the largest rate increase followed by tropical and temperate zones. Changes in climate and eutrophication in the past three decades drove N removal and N₂O release at rates of 108-164 and 12-17 Gg N yr^-1. The N removal is equivalent to carbon loss of 115-176 Gg C yr^-1 based on the stoichiometry of organic matter consumption. Predicted scenarios of warming and nitrate enrichment would increase denitrification and N₂O emissions by 4.4-24.8% in China’ coastal wetlands by 2050s. Overall, coastal wetlands have been and will continue to be effective filters of nitrogen pollution.

Primary Presenter: Fenfang Wang, Xiamen University (ffwang@stu.xmu.edu.cn)

Authors:

Isaac Santos, University of Gothenburg  (isaac.santos@gu.se)

Ruifeng Yan, Xiamen University  (yanruifeng@stu.xmu.edu.cn)

Shibin Zhao, Ocean University of China  (ouc_zshib@163.com)

Nengwang Chen, Xiamen University  (nwchen@xmu.edu.cn)