Spatial and temporal variations of nitrous oxide flux between coastal marsh and the atmosphere in the Yellow River estuary of China

To investigate the spatial and seasonal variations of nitrous oxide (N(2)O) fluxes and understand the key controlling factors, we explored N(2)O fluxes and environmental variables in high marsh (HM), middle marsh (MM), low marsh (LM), and mudflat (MF) in the Yellow River estuary throughout a year. Fluxes of N(2)O differed significantly between sampling periods as well as between sampling positions. During all times of day and the seasons measured, N(2)O fluxes ranged from −0.0051 to 0.0805 mg N(2)O m(−2) h(−1), and high N(2)O emissions occurred during spring (0.0278 mg N(2)O m(−2) h(−1)) and winter (0.0139 mg N(2)O m(−2) h(−1)) while low fluxes were observed during summer (0.0065 mg N(2)O m(−2) h(−1)) and autumn (0.0060 mg N(2)O m(−2) h(−1)). The annual average N(2)O flux from the intertidal zone was 0.0117 mg N(2)O m(−2) h(−1), and the cumulative N(2)O emission throughout a year was 113.03 mg N(2)O m(−2), indicating that coastal marsh acted as N(2)O source. Over all seasons, N(2)O fluxes from the four marshes were significantly different (p < 0.05), in the order of HM (0.0256 ± 0.0040 mg N(2)O m(−2) h(−1)) > MF (0.0107 ± 0.0027 mg N(2)O m(−2) h(−1)) > LM (0.0073 ± 0.0020 mg N(2)O m(−2) h(−1)) > MM (0.0026 ± 0.0011 mg N(2)O m(−2) h(−1)). Temporal variations of N(2)O emissions were related to the vegetations (Suaeda salsa, Phragmites australis, and Tamarix chinensis) and the limited C and mineral N in soils during summer and autumn and the frequent freeze/thaw cycles in soils during spring and winter, while spatial variations were mainly affected by tidal fluctuation and plant composition at spatial scale. This study indicated the importance of seasonal N(2)O contributions (particularly during non-growing season) to the estimation of local N(2)O inventory, and highlighted both the large spatial variation of N(2)O fluxes across the coastal marsh (CV = 158.31 %) and the potential effect of exogenous nitrogen loading to the Yellow River estuary on N(2)O emission should be considered before the annual or local N(2)O inventory was evaluated accurately.