渤海湾典型闸控入海河流水体N2O释放研究

为探究弱水动力条件下, 典型滨海地区水体N₂O释放通量及其主控因素, 于2019年7月和8月(夏季)和11月(冬季初期)对以大清河-独流减河-北大港湿地为代表的渤海湾弱水动力条件河流开展水样采集与分析工作.结果表明: N₂O浓度变化范围为0.4~184.5nmol/L, N₂O饱和度的变化范围为7.2%~2740%, 其中近90%的样品处于过饱和状态, 表明该研究区是潜在的N₂O释放源.N₂O水-气界面释放通量为-0.3~6.7μmol/(m²·h), 夏季水体N₂O的释放通量高于冬季.降雨前后N₂O浓度出现明显波动, 相同点位降雨前后N₂O浓度的变化值为-15.2~63.9nmol/L, 独流减河上游农业区N₂O浓度的平均增加量(22.1nmol/L)显著高于下游(1.3nmol/L), 降雨驱动了流域氮素的运移, 促进了水体N₂O释放.相关性分析表明, 水体N₂O的浓度受反应物浓度、水体盐度共同调控.通过计算得到该滨海地区弱水动力条件下河流N₂O的排放因子为0.0073, 表明气候变化委员会(IPCC)默认值0.0026可能低估了该地区间接N₂O释放.

N2O release from the water bodies of typical gate controlling tributaries of Bohai Bay

To explore the spatiotemporal variation in N₂O in typical coastal zone and its main controlling factors under weak hydrodynamic conditions, water samples were collected from coastal rivers and wetlands (Daqing River-Duliujian River-Beidagang wetland) in July and August (Summer) and November (the beginning of Winter) in 2019. The results show that the concentration of N₂O varied between 0.4~184.5nmol/L. The saturation of N₂O ranged from 7.2%~2740%, and 90% of the samples were oversaturated, indicating that the study area was a potential source of N₂O. The N₂O release flux at the water-gas interface ranged from -0.3~6.7μmol/(m²·h), while the N₂O exchange flux in summer was higher than that in winter. The study also found that the N₂O concentration fluctuated significantly before and after rainfall, and the variation in N₂O ranged from -15.2~63.9nmol/L at same sites before and after rainfall. The average increase in N₂O concentration was significantly higher in the upper reaches (22.1nmol/L) than in the downstream (1.3nmol/L), indicating that rainfall drove the transportation of nitrogen species and accelerated N₂O release. The salinity and NO₃^--N concentration had significant effect on N₂O concentration. The N₂O emission factor of the tributaties under the weak hydrodynamic conditions in coastal zone was estimated to be 0.0073, higher than the default value of 0.0026 defined by IPCC. Therefore, the N₂O budget in the coastal zone may underestimate the indirect N₂O emissions by using the IPCC threshold value.