Spatial and temporal variations of nitrous oxide flux between coastal marsh and the atmosphere in the Yellow River estuary of China
2014
Sun, Zhigao | Wang, Lingling | Mou, Xiaojie | Jiang, Huanhuan | Sun, Wanlong
To investigate the spatial and seasonal variations of nitrous oxide (N₂O) fluxes and understand the key controlling factors, we explored N₂O 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 N₂O differed significantly between sampling periods as well as between sampling positions. During all times of day and the seasons measured, N₂O fluxes ranged from −0.0051 to 0.0805 mg N₂O m⁻² h⁻¹, and high N₂O emissions occurred during spring (0.0278 mg N₂O m⁻² h⁻¹) and winter (0.0139 mg N₂O m⁻² h⁻¹) while low fluxes were observed during summer (0.0065 mg N₂O m⁻² h⁻¹) and autumn (0.0060 mg N₂O m⁻² h⁻¹). The annual average N₂O flux from the intertidal zone was 0.0117 mg N₂O m⁻² h⁻¹, and the cumulative N₂O emission throughout a year was 113.03 mg N₂O m⁻², indicating that coastal marsh acted as N₂O source. Over all seasons, N₂O fluxes from the four marshes were significantly different (p < 0.05), in the order of HM (0.0256 ± 0.0040 mg N₂O m⁻² h⁻¹) > MF (0.0107 ± 0.0027 mg N₂O m⁻² h⁻¹) > LM (0.0073 ± 0.0020 mg N₂O m⁻² h⁻¹) > MM (0.0026 ± 0.0011 mg N₂O m⁻² h⁻¹). Temporal variations of N₂O 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 N₂O contributions (particularly during non-growing season) to the estimation of local N₂O inventory, and highlighted both the large spatial variation of N₂O fluxes across the coastal marsh (CV = 158.31 %) and the potential effect of exogenous nitrogen loading to the Yellow River estuary on N₂O emission should be considered before the annual or local N₂O inventory was evaluated accurately.
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