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 degrees 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 mu mol 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.