地下水NO_3^-氮与氧同位素研究进展

An Overview of the Study on Nitrogen and Oxygen Isotopes of Nitrate in Groundwater

人为活动通常是地下水硝酸盐污染的主要原因。不同来源的NO3-具有不同的氮、氧同位素组成,利用地下水NO3-中的δ15N和δ18O值可有效识别地下水硝酸盐污染的来源。引起地下水中NO3-含量显著减少的不同物理、化学和生物过程,所产生的氮、氧同位素分馏效应有明显差别。地下水系统中反硝化作用发生时,NO3-中氮和氧同位素分馏系数呈一定比例。因此NO3-中δ15N和δ18O值也是示踪地下水硝酸盐循环,尤其是反硝化作用的有效手段。利用NO3-中氮和氧双同位素,并与其他环境同位素及化学分析技术相结合,示踪NO3-来源及其循环是地下水硝酸盐污染研究的重要方向之一。综述了利用地下水硝酸盐中氮和氧同位素识别NO3-污染源与循环的研究进展,简述了近年迅速发展的阴离子交换树脂取样法,概述了此方面研究存在的主要问题,并展望了今后的研究方向。

Nitrate contamination of groundwater often results from human activities. Stable isotope ratios of N （^15N/^14N） and O （^18O/^160） in NO3 can be used to aid in distinguishing various sources of NO3 in groundwater effectively because values of δ^15N-NO3^- and δ^18O-NO3 in groundwater vary with the sources of nitrate. Different physical, chemical and biological processes may lead to distinctive nitrogen and oxygen isotope fractionations. When denitrifieation occurs in groundwater, the enrichment for ^15N in NO3^- is higher by a factor of about 2.0 than for ^18O in NO3^-. Thus, a dual isotopic approach of measuring both δ^15N and δ^18O in NO3^- could be employed to trace nitrate cycles in groundwater, especially the occurrence of denitrification. Use of both N and O isotopes in NO3^- combined with other environmental isotopic and chemical methods to trace nitrate sources and cycles are an important way in the investigation of nitrate contamination of groundwater. As to techniques for the measurement of ^15N/^14N and ^18O/^160 compositions of nitrate, a newly developed method for nitrate concentration using anion exchange resins has been applied in more and more studies because it is convenient and economical. In this paper, the progress of identifying NO3^- sources and its cycles in groundwater with the aid of δ^15N-NO3^- and δ^18O-NO3^- is reviewed. Future possible developments are put forward along with some problems in this research field.