利用氮稳定同位素法、综合常规水样监测以及微环境培养方法探讨了五川农业溪流沿程氮的迁移转化过程。结果表明,溪流沿程nO3-n浓度变化范围为0.5--4.5 Mg l-1,平均为1.26 Mg l-1,且多数月份总体上呈逐渐升高的趋势,同时nO-3的δ15n存在降低趋势,两者呈线性负相关(r2>0.80),表现明显的硝化过程典型特征。各采样点的nO2-n、dO、dOC浓度与nO3-n也存在一定的线性相关关系,说明了硝化过程的发生和氮在不同形态之间的转化。溪流水体微环境培养实验证明了水体中的nH4-n和nO3-n浓度在培养期内并无明显变化,以上数据和相关关系充分表明了流域沿程地表径流氮素输入和溪流系统沉积物和水体界面的硝化过程共同作用可能是五川溪流沿程nO3-n与nH4-n浓度升高,而nO-3的δ15n值减小的主要原因。因此,在农业流域的污染源评价中,需要重新审视和调查河道系统内部氮的转化和贡献。Nitrogen isotope and traditional water sampling,together with microcosm incubations were used to investigate processes of nitrogen downstream transports and transformations within the Wuchuan stream.Results showed NO3-N concentrations varied downstream ranging from 0.5 to 4.5 mg L-1 for most of sampling months with a mean of 1.26 mg L-1 in the stream.However,nitrate isotope δ15N decreased downstream,comparing to increased trend in NO3-N concentration.The relationship between downstream NO3-N concentrations and nitrate δ15N with a R2 exceeding 0.8 can be characterized as a typical process of nitrification.The relationships between NO3-N concentrations and NO2-N,dissolved oxygen,dissolved organic carbon concentrations for the sampling sites also indicated strong nitrification processes and consequent nitrogen transformations between nitrogen forms in the stream.Microcosm study of surface water from the stream showed that no significant change in NH4-N and NO3-N concentrations occurred during the five-day incubations.All the information and relationships showed that the downstream increases in NH4-N and NO3-N concentrations, and the downstream decreases in nitrate δ15N within the stream obviously resulted from the nitrogen input from surface runoff flowing into the channel,and also nitrogen transformations by nitrification occurred between stream sediment and overlying water within the channel.Therefore,it is essential to take the sources from nitrogen transformations within streams into account and to evaluate their contributions in pollution assessments at catchment scales.国家自然科学基金资助项目(40671116);福建省自然科学基金重点资助项目(D0720002);国家教育部新世纪优秀人才支持计划资助项目;福建省高校新世纪优秀人才支持计划资助项目;厦门市科技计划指导性资助项目(3502Z20077014
