闽江河口表层水体氧化亚氮释放时空变化特征及其影响因素

In this study, seasonal variability of N₂O concentrations and fluxes and associated environmental factors were investigated in the upper section（urban estuary）, the middle section and the lower section（coastal section outside the estuary）of Min River Estuary. The results indicated that N₂O concentrations, N₂O saturations and N₂O fluxes were in a range of 0.99~55.92 nmol·L^-1, 8.0%~396%, and -5.21~7.91 μg·m^-2·h^-1. Water N₂O was supersaturated in July（summer）, September（autumn）and December（winter）, representing the "source" of N₂O emission. However, N₂O emissions exhibited the "sink" in April（spring）. N₂O fluxes were significantly higher in summer, autumn and winter than in spring, and decreased from the upper to lower estuary. Indirect N₂O emission factors ranged from 0.004% to 0.128%, which was significantly lower than the IPCC default value（0.25%）. Temperature, salinity, pH, NO₃^-, DO and suspended particulate matter were the crucial factors affecting dissolved N₂O concentrations and fluxes. Therefore, seasonal changes and human activities can trigger the large variability of N₂O emissions, leading to the increasing uncertainty of N₂O projections.