Mechanism underlying revetment effects on the spatial distribution of nitrogen removal and N2O emissions in riparian zones at summer

Study Region, Shanghai, China, Study Focus Urban riparian zones can mitigate or even control nitrogen pollution in rivers through nitrification and denitrification processes. However, these processes also produce N 2 O, a potent greenhouse gas. During urbanization, various types of revetments have been constructed in riparian zones. These revetments alter the exchange of materials and energy between the riparian zone and the river, which in turn affects the nitrification and denitrification processes in the riparian zone. However, the mechanisms by which revetments impact nitrogen removal and N 2 O emissions in riparian zones are not yet clear, and the ways in which revetments balance nitrogen removal and N 2 O emissions remain unknown. Therefore, in a single river section, natural (NR), permeable (PR), and impervious revetment (IR) types were replicated. Measurements are taken of nitrogen removal, N 2 O emissions, and related environmental indicators in both the river-riparian interface (RRI) and the riparian zone area outside the RRI (RZ). The study analyzes the differences in environmental factors, nitrification and denitrification potentials, and N 2 O emission rates among the different revetments to identify the main factors affecting nitrogen removal and N 2 O emissions in the riparian zone. It also explores the potential mechanisms by which revetments influence the spatial distribution of nitrogen removal and N 2 O emissions in the summer riparian zone. New Hydrological Insights for the Region: PR exhibit greater denitrification potential and lower N 2 O emission rates. The denitrification potential is higher in the RRI compared to RZ, while the N 2 O emission rate is lower than in RZ. nirK is the primary factor influencing denitrification potential, whereas nosZII predominantly affects N 2 O emissions. The lower soil carbon-to-nitrogen ratio in PR increases the abundance of nirK , thereby enhancing the riparian zone's denitrification potential. Moreover, greater aboveground vegetation biomass increases the abundance of nosZII , reducing the N 2 O emission rate. The study results could provide guidance for urban ecological restoration and greenhouse gas emission reduction. • River-riparian interface has stronger denitrification potential and less N 2 O emissions. • Permeable revetment has stronger denitrification ability and less N 2 O emission. • Lower carbon-to-nitrogen ratio and higher nirK abundance enhance nitrogen removal. • Higher aboveground biomass and noszII abundance reduce N 2 O emissions.