深圳再生水补水河流溶解N2O空间分布和产生机制

为了探究在再生水回补城市河流的条件下河流N₂O的微生物产生过程及其空间变化特征，以深圳市西乡河为研究对象，分析了河水中c（溶解性N₂O）、c（NH₄+-N）、c（NO₃--N）、δ15Nbulk-N₂O、δ18O-N₂O、同位素异位体位嗜值（site preference，SP）及其他环境因子，并基于端元混合模型和同位素分馏模型定量计算硝化和反硝化作用对河水中N₂O贡献百分比.结果表明:①随着流速降低，西乡河河水从上游的好氧环境逐渐发育成中下游的厌氧环境.②再生水进入西乡河后河水c（溶解性N₂O）从1.36 μmol/L沿程降至0.19 μmol/L；相关性分析表明，影响c（溶解性N₂O）的主要因素为ρ（DO）（R2=0.800，P < 0.01）和c（CH₄）（R2=-0.736，P < 0.01）.③硝化和反硝化作用对河水中N₂O贡献率分别为14.36%~80.53%和19.47%~85.64%；N₂O的来源在好氧河段中以硝化作用为主，在厌氧河段则以反硝化作用为主；N₂O还原成N₂的比例与ρ（DO）具有显著负相关关系（R2=-0.782，P < 0.01）.研究显示，再生水回补城市河流引入了较高质量浓度的N₂O和NO₃--N，而河道的厌氧环境促进河水中N₂O还原成N₂，下游河流成为N₂O的汇. 

Spatial Variation of Dissolved N2O and Its Underlying Processes in River Affected by Treated Wastewater Effluent in Shenzhen

In order to reveal the spatial variation and 6 production process of dissolved N₂O affected by reclaimed water, the dissolved c(N₂O), c(NH₄+-N) and c(NO₃--N), isotopomer signatures of N₂O (δ15Nbulk-N₂O, δ18O-N₂O and SP) and other environmental factors were measured in the Xixiang River, Shenzhen City. The contributions of nitrification and denitrification to N₂O in the river were qualified based on the end member model and isotope fractionation model. The results showed that:(1) The oxic condition in the upper reach changed gradually to the anoxic condition in the middle and lower reaches due to the slow flow velocity downstream; (2) c(N₂O) decreased from 1.36 μmol/L to 0.19 μmol/L along the river, and it was mainly controlled by ρ(DO) (R2=0.800, P < 0.01) and c(CH₄)(R2=-0.736, P < 0.01); (3) The contribution of nitrification and denitrification for N₂O production in the river were 14.36%-80.53% and 19.47%-85.64%, respectively. N₂O was produced from nitrification in oxic condition reach, and from denitrification in the anoxic reach. There was a significant negative correlation between the reduction ratio of N₂O to N₂ and ρ(DO) (R2=-0.782, P < 0.01). The research showed that the reclaimed water brought highly dissolved c(N₂O) and c(NO₃--N) into the urban river, resulting in the potential emission of N₂O, and the river became a sink of N₂O at downstream.