氮氧同位素联合稳定同位素模型解析水源地氮源

Contribution of Nitrogen Sources in Water Sources by Combining Nitrogen and Oxygen Isotopes and SIAR

找出作为优质水源地的水库氮的来源对控制其富营养化问题非常重要.本研究选取杭嘉湖地区的4个水库(青山水库、对河口水库、四岭水库和里畈水库),利用氮、氧同位素技术结合稳定同位素模型(stable isotope analysis in R,SIAR),对水库的硝酸盐(NO_3^-)来源进行了识别并计算了各污染源的贡献率.结果表明,4个水库中存在严重的氮污染,以硝酸盐为主,受人类活动干扰较大的青山水库,污染严重.4个水库86%以上的δ^(18)O值小于10‰,93%样品的δ^(15)N/δ^(18)O值小于1.3,说明水库中硝化反应明显而反硝化作用不显著.4个水库硝酸盐的主要来源是化学肥料和土壤氮,两者的贡献率为75%~82%,种植业面源污染给水源地水库带来的氮污染已非常严重;青山水库硝酸盐的来源还包括贡献率为25%的生活污水及粪肥、贡献率为7%的降水和贡献率为6%的工业废水,说明在人类活动强度大的区域生活污水及粪肥的污染也不可忽视;对河口水库、四岭水库和里畈水库硝酸盐的来源还包括降水,其贡献率分别为21%、24%和15%,可见在人为干扰较少的地区,降水对于水体硝酸盐的影响也不可忽略.

It is very important to identify nitrate sources in reservoirs that serve as high quality water sources to control its eutrophication. Stable isotopes（ δ^（15）N and δ^（18）O） and a Bayesian model（ stable isotope analysis in R,SIAR） were applied to identify nitrate sources and estimate the proportional contributions of multiple nitrate sources in four reservoirs（ Qingshan reservoir,Duihekou reservoir,Siling reservoir,and Lifan reservoir） that serve as sources of drinking water in the Hangjiahu area,one of the most densely populated and most quickly developing areas in East China. It was shown that nitrogen pollution,which was dominated by nitrate（ NO3^-）,existed in the four reservoirs. Greater human activities caused more nitrogen pollution（ average NO3^- concentration 0. 21 mmol·L^（-1）） in the Qingshan reservoir. A significant positive correlation（ P 0. 01） was observed between Cl-and NO3^-. The analysis of the water in the Duihekou reservoir,Siling reservoir,and Lifan reservoir,with lower Cl-concentrations and higher NO3^-/Clratios,suggested that chemical fertilizer was the main source,while the analysis of the water in the Qingshan reservoir,with medium Cl-concentrations and NO3^-/Cl^- ratios,indicated a mixture of NO3^- sources. The δ^（15）N ranged from 0. 9‰ to 7. 2‰,and the δ^（18）O ranged from 2. 8‰ to 14. 1‰ in the four reservoirs. The δ^（18）O values in more than 86% of the water samples were less than 10‰,and the δ^（15）N/δ^（18）O values in 93% of the water samples were less than 1. 3. It was identified that nitrification rather than denitrification acted as the primary N cycling process in the four reservoirs. SIAR was used to estimate the proportional contribution of five NO3^- sources（ industrial wastewater,sewage/manure,chemical fertilizer,soil nitrogen,and precipitation） in the Qingshan reservoir and of three NO-3 sources（ chemical fertilizer,soil nitrogen,and precipitation） in the Duihekou reservoir,Siling reservoir,and Lifan reservoir. The source apportionment results showed that chemical fertilizers and soil nitrogen were the dominant nitrate sources and their contributions were 75%-82%. It was revealed that nitrogen pollution in the water source reservoir caused by cropping non-point source pollution was very serious. Nitrate source contributions in Qingshan reservoir also included sewage/manure（ 25%）,soil nitrogen（ 7%）,and precipitation（ 6%）,indicating that nitrogen pollution by sewage/manure should not be ignored in the higher human activity areas. The nitrate source in the Duihekou reservoir,Siling reservoir,and Lifan reservoir also included precipitation,with the nitrate contribution from precipitation at 21%,24%,and 15%,respectively. It was suggested that precipitation contributed more nitrate to the water in areas with less human activity.