天津市滨海河流N_(2)O扩散通量及控制因子

Diffusive Fluxes and Controls of N_(2)O from Coastal Rivers in Tianjin City

河流是大气温室气体重要的排放源.为了探讨天津市典型景观滨海河流N_(2)O释放空间特征及影响因素,以天津市6条不同土地利用类型的滨海河流为研究对象,通过顶空-气相色谱法测定了N_(2)O浓度、饱和度和扩散通量.结果表明,天津市不同景观河流N_(2)O浓度都处于过饱和状态,表现为大气N_(2)O的源;N_(2)O浓度、饱和度和扩散通量均值为(23.85±15.20)nmol·L^(-1)、(309.71±197.38)%和(27.04±16.46)μmol·(m^(2)·d)^(-1),范围分别为12.70~115.69 nmol·L^(-1)、164%~1502%和9.17~244.79μmol·(m^(2)·d)^(-1).天津市不同土地利用类型河流N_(2)O浓度和扩散通量具有较大的空间异质性,表现为:排污河>城市河流>郊区河流>农业河流.天津滨海河流N_(2)O浓度主要受到盐度、氮磷营养元素和碳源的影响.NO_(3)^(-)-N和TP对N_(2)O扩散通量差异的贡献较大.天津河流N_(2)O产生和释放与氮循环过程密切相关,不同形态氮对河流N_(2)O扩散通量贡献存在差异.盐度梯度对城市河流和排污河N_(2)O释放产生相反的影响.天津河流排污河的N_(2)O扩散通量显著高于其他类型河流,未来由于城镇化的发展以及城市土地的扩张,更多的管理措施应聚焦于排污河的废水处理厂下游、城市河流的入海口和郊区河流的居民聚集区等热点区域,从而减少温室气体的释放.

Rivers are an important emission source of greenhouse gases.To explore the spatial characteristics and influencing factors of N_(2)O emission from the coastal rivers in Tianjin City,six rivers into the Bohai Sea from different land-use types were selected,and the N_(2)O concentrations,saturation,and diffusive fluxes were measured using the headspace-gas chromatography method.The N_(2)O concentration was in supersaturation,and the rivers were the source of atmospheric N_(2)O.The average concentration,saturation,and diffusive fluxes of N_(2)O were(23.85±15.20)nmol·L^(-1),(309.71±197.38)%,and(27.04±16.46)μmol·(m^(2)·d)^(-1),with the ranges of 12.70-115.69 nmol·L^(-1),164%-1502%,and 9.17-244.79μmol·(m^(2)·d)^(-1),respectively.The N_(2)O concentrations and diffusive fluxes of the rivers presented great spatial heterogeneity,with the sewage river(Huangdipai River)>urban river(Haihe River main stream,Jiyun River)>suburban river(Duliujian River,Yongding Xinhe River)>agricultural river(Chaobai Xinhe River).The N_(2)O concentration and diffusion fluxes were significantly correlated with salinity,nutrients,and carbon sources.NO_(3)^(-)-N and TP contributed greatly to the diffusive flux differences.N_(2)O production and emission greatly related to the nitrogen cycle process in the Tianjin River,and different forms of nitrogen variously contributed to N_(2)O diffusive fluxes.The salinity gradient had the opposite effect on the N_(2)O emission in urban rivers and drainage rivers.The N_(2)O diffusive fluxes of the sewage river in Tianjin were significantly higher than that of other river types.In the future,due to the development of urbanization and the expansion of urban land,more management measures should focus on the hotspots such as the downstream of wastewater treatment plants of sewage rivers,the estuaries of urban rivers,and the residential gathering areas of suburban rivers to reduce N_(2)O emission.