长江溶存氧化亚氮的分布与释放

Distribution and emission of nitrous oxide from the Changjiang River

于2008年1月对长江宜昌到徐六泾段干流以及部分湖泊和支流入江口进行了调查,并于2007年6月到2008年5月对长江徐六泾进行了逐月调查,采样测定了长江溶存N2O的浓度并选择合适的模型估算了其释放通量.结果表明,2008年1月长江表层河水中N2O的平均浓度为(22.0±3.5)nmo·lL-1,均处于过饱和状态,平均饱和度为180%±33%,长江向大气释放N2O通量平均为(13.7±14.6)μmol·m-·2d-1.冬季长江溶存N2O的分布规律为下游溶存N2O浓度高于中游,支流及湖泊高于干流.长江徐六泾段河水中N2O全年平均浓度为(19.4±7.3)nmol·L-1,呈现明显季节变化特征.长江徐六泾段河水中N2O平均释放通量为(43.9±24.9)μmol·m-2·d-1,夏季最高可达80.7μmol·m-·2d-1.初步估算出长江每年向大气释放N2O-N的量为12.0Gg·a-1,约占整个中国N2O排放量的1.1%.而长江输入东、黄海N2O-N的年通量为0.5Gg·a-1,对长江口及其邻近海域N2O分布及氮的生物地球化学循环有重要影响.

Field surveys from Yichang to Zhenjiang along the Changjiang （also known as the Yangtze River） were carried out in January 2008, and monthly surveys at Xuliujing of the Changjiang Estuary were carried out from June 2007 to May 2008. Concentrations of N2O in the Changjiang were measured and the atmospheric N2O fluxes were estimated. The mean N2O concentration in surface waters of the Changjiang was （22. 0 ± 3. 5 ） nmol·L^-1 , and the surface water was persistently supersaturated in N2O with an average saturation of 180%± 33% and water-to-air flux of （13.7 ± 14.6 ） μmol·m^-2·d^-1. N2O concentrations in the downstream of Changjiang were higher than those in midstream, and N2O in tributaries and lakes were higher than those in the mainstream. N2O concentrations at Xuliujing was averaged to be （ 19.4 ± 7. 3 ） nmol·L^-1, and showed obvious seasonal variations. The average air-water flux was （43.9 ＋ 24.9 ） μmol·m^-2·d^-1 at Xuliujing, the high value appeared in summer, about 80.7μmol·m^-2·d^-1 Changjiang is estimated to contribute 12. 0 Gg N2O-N to the atmosphere annually, accounting for about 1. 1% of N2O emissions from China. The dissolved N2O-N input to the East China Sea from the Changjiang was estimated to be 0.5 Gg·a^-1 , and plays an important role in the blogeochemical cycling of N in the estuary.