多种同位素手段的硝酸盐污染源解析:以会仙湿地为例

Identification of Nitrate Pollution Sources Through Various Isotopic Methods: A Case Study of the Huixian Wetland

近年来,湿地在人类掠夺性开发下生态环境正不断恶化.其中,硝酸盐污染就是湿地生态环境面临的一类主要问题.本文以会仙岩溶湿地为研究对象,为查明导致湿地水体硝酸盐升高的主要因素,利用^(15)N(NO_3^-)、^(18)O(NO_3^-)同位素手段确定区内硝酸盐污染的主要来源,并借助SIAR模型确定各类污染源的贡献率.在此基础上,通过^(13)C_(DIC)同位素定性描述地下水的径流条件,以此探究硝酸根浓度的空间分布与水循环的关系.结果表明,影响研究区水体中硝酸根浓度的主要因素有3个方面,动物粪便及生活污水、化肥中NO_3^-和土壤氮,其对硝酸盐污染的贡献率均值分别为39.1%、32.2%和28.5%.^(13)C_(DIC)同位素结果显示,轻^(13)C_(DIC)表明其地下水径流条件好,其对应的NO_3^-浓度值一般较低,而重^(13)C_(DIC)对应的NO_3^-浓度值一般较高.由此可知,地下水径流条件的好坏也一定程度地影响了NO_3^-浓度的分布.

In recent years, the ecological environment of wetlands has deteriorated under the predatory exploitation of human beings. Nitrate pollution is a major problem faced by wetland ecosystems. In this paper, Huixian karst wetland was selected as a study area to identify the main factors leading to the increase of nitrate in wetland water. The main sources of nitrate pollution in the area were determined by means of ISN（ NO3^- ） and ^15O（ NO3^- ） isotopes. The contribution rate of all types of pollution sources was determined with the SIAR model. To explore the relationship between the spatial distribution of the nitrate concentration and the groundwater runoff conditions, the ^13CDIc isotopes were used to qualitatively characterize the runoff conditions of the groundwater. The results show that there are three main factors affecting the nitrate concentration in the study area： animal manure and domestic sewage, NO3^- in chemical fertilizer, and soil nitrogen. The average contribution rates to nitrate pollution are 39. 1% , 32.2% , and 28.5% respectively. The ^13CDIc isotope data clarify that a light ^13CDIC reflects better groundwater runoff conditions. The concentration of NO3 is generally lower, while the NO3 concentration corresponding to heavy ^13CDIc is generally higher. The condition of the groundwater runoff to a certain extent also affects the distribution of the NO3^- concentration.