Quality of Sediment Organic Matter Determines the Intertidal N₂O Response to Global Warming

Estuaries and coasts are areas of intense biogeochemical cycling and are sensitive to global climate change. However, the effect of temperature increase on the emissions of the powerful greenhouse gas nitrous oxide (N₂O) in different estuarine and coastal areas is still uncertain. In this study, we used laboratory incubation experiments to investigate increasing temperatures (12, 25, and 35°C) and tidal effects on N₂O fluxes in intertidal sediments from the East China coast (ECC). Overall, the ECC acts as a net source of atmospheric N₂O and exhibited considerable spatial variability over three orders of magnitude (from −0.17 to 8.4 μmol m⁻² h⁻¹). The warming promoted N₂O emissions in most intertidal areas, while reducing N₂O emissions at some sampling sites. In addition, the overall effect of flooding on N₂O emissions changed from a positive to a negative effect with increasing temperature. By combining the sediment properties of all the sampling sites, we found that large differences in N₂O emissions at the same amended floodwater nitrogen concentration were due to the quality and quantity of sediment organic matter. Sediment derived mainly from marine sources emitted more N₂O than sediment derived from terrestrial sources. This suggests that the mangroves, salt marshes, and intertidal zones of estuaries have a mitigating effect on N₂O emissions due to their elevated terrestrial organic matter inputs. This research improves our understanding of the impact of future global climatic changes on intertidal N₂O fluxes, which can inform future studies and models and can be used to constrain intertidal N₂O emissions.