西安浐河、灞河硝酸盐氮同位素特征及污染源示踪探讨

Nitrogen Isotopic Characteristics of Nitrate and Contamination Source Tracing of the Chanhe River and the Bahe River in Xi'an

硝酸盐是河流主要污染物之一,近些年,对西安市各主要河流监测发现硝酸盐氮污染有加重的趋势,然而对这些河流硝酸盐氮污染源尚缺乏足够的认识。由于不同氮来源的硝酸盐氮同位素组成不同,氮同位素示踪技术被应用到河流硝酸盐污染源方面的研究。笔者通过对西安市东部补给水源(浐河、灞河)无机氮含量变化调查,并利用河水硝酸盐氮同位素组成和特征,初步讨论了这两条河流硝酸盐氮的可能污染源。结果显示,浐河、灞河在源头附近δ15N-NO3-是由岩石和天然土壤中的有机氮起主导因素;中游δ15N值偏重是由于农业活动施加化肥引起;下游δ15N达到最高,说明工业废水、生活污水和粪肥的影响占主导。该结论为以后深入研究陕西地区河流水质提供基础。

Nitrate is one of the dominant contaminations in rivers. In recent years, some researchers have studied the dominant contaminations in the main rivers of Xi＇an City, and found that the nitrate contamination tended to become increasingly heavier. However, the knowledge about the sources of the nitrate contamination in the river remains insufficient. The nitrogen isotope tracing technology has been widely used in the research of the nitrate contamination, this is because different nitrogen sources have different nitrogen isotopic compositions. In this paper, the concentration and nitrogen isotope characteristics of water nitrate from the Chanhe River and the Babe River around Xi＇an City were investigated, and the nitrate potential contamination sources were analyzed. The results show that the δ^15N- NO3 - values in the headstream of the Chanhe River and the Babe River are the lowest and attributed to the organic nitrogen from rocks and natural soil, that the higher δ^15N values in the middle reaches are caused by the joint action of natural soil, fertilizer and manure, and that the highest δ^15N values in the lower reaches of the two rivers result mainly from industrial wastewater, sewage and manure in this area. It is concluded that nitrogen isotope can provide basic information for tracing nitrate sources of the rivers in Xi＇ an City.