太子河下游河流硝酸盐来源及其迁移转化过程

Identification of Nitrate Sources and the Fate of Nitrate in Downstream Areas:A Case Study in the Taizi River Basin

2016年5月(枯水期)和2016年8月(丰水期)分别在太子河下游采集河流表层水样14个.为了识别河流硝酸盐来源及迁移转化过程,分别采用离子交换法,叠氮法和CO_2-H_2O平衡法测定水样的ρ(Cl-)、ρ(NO_3^-)、δ^(15)N-NO_3^-、δ^(18)O-NO_3^-值,测定δ^(18)O-H_2O.结果表明:不同采样期,硝酸盐主要来自于多种源的混合.枯水期,北沙河上游支流硝酸盐来源主要是土壤N及生活污水及畜禽粪便,中下游硝酸盐主要来自于化学肥料和生活污水及畜禽粪便.南沙河硝酸盐主要来自于生活污水及畜禽粪便.海城河上游、中游和下游硝酸盐分别来自于土壤N,生活污水及畜禽粪便和化学肥料,生活污水及畜禽粪便.丰水期,北沙河硝酸盐来源可能主要是土壤N、化学肥料和生活废水及畜禽粪便.南沙河和海城河中下游硝酸盐主要来自于化学肥料及生活废水及畜禽粪便,海城河上游河流硝酸盐主要来自于土壤N和化学肥料.从枯水期至丰水期,ρ(NO_3^-)、ρ(NH_4^+-N)均呈现降低的趋势,而δ^(15)N-NO_3^-值有增加的趋势,说明丰水期可能发生了氨的挥发和硝酸盐的反硝化过程.丰水期δ^(15)N-NO_3^-与1/ρ(NO_3^-)呈轻微的正相关关系,说明丰水期河流发生了简单的混合过程.本研究的结果可为平原区域的硝酸盐污染来源的季节差异研究提供参考.

A total of 14 samples were collected in May 2016（dry season） and August 2016（wet season） in the downstream area of the Taizi River. δ^15 N-NO3^- and δ^18O-NO3^- were determined using the azide method,and δ^18O-H2O was determined using a CO2-H2O equilibration technique. To identify NO3^- sources and transformations in the downstream area of Taizi River Basin,ion chromatography,Nessler＇s reagent spectrophotometry, the azide method, and CO2-H2O equilibration methods were utilized to determine the concentrations of NO3^-,Cl-,NH4^＋-N,and isotopic compositions（δ^15 N and δ^18O） of NO3^- and the δ^18O-H2O in surface water. The results showed that the NO3^- was mainly derived from mixed sources. During the dry season,the nitrate in the surface water was derived from soil nitrogen,manure,and sewage in the upper reaches,and mainly derived from synthetic fertilizer,manure,and sewage in the middle and lower reaches of the Beisha River. The nitrate was mainly derived from manure and sewage in the Nansha River. The nitrate was mainly derived from soil nitrogen in the upper reaches,mainly derived from synthetic fertilizer,manure,and sewage in the middle reaches,and mainly derived from manure and sewage in the lower reaches of the Haicheng River. During the wet season,the nitrate sources in surface water were soil nitrogen,synthetic fertilizer,manure,and sewage in the Beisha River; synthetic fertilizer,manure,and sewage in the middle and lower reaches of the Haicheng River and the Nansha River; and soil nitrogen and synthetic fertilizer in the upper reaches of the Haicheng River. NO3^- and NH4^＋-N concentrations decreased with increasing δ^15 N-NO3^- from the dry season to the wet season,indicating that volatilization of NH4^＋-N and denitrification of NO3^- might occur during the wet season. There is a slightly positive relationship between the reciprocal of the concentration of 1/ρ（NO3^-） and δ^15 N-NO3^- during the wet season,indicating that mixing processes occurred in surface water. The results will provide information on nitrate sources during seasonal variations in the plain areas.