To determine the characteristics of nitrogen contamination and its migration conversion process in Eastern Guilin karst aquifer, 27 samples of ground and surface water were collected during the rainy season and dry season respectively. The results showed that as the main form of inorganic nitrogen, NO3--N of groundwater in Eastern Guilin was highly contaminated. In rainy season, average concentration of NO3--N was 12.5mg/L for the groundwater samples, exceeding groundwater drinking standard line (10mg/L) suggested by the world health organization (WHO). In dry season, the average concentration of NO3--N in groundwater was 8.8mg/L. Although it had a significant decrease, also it still stayed on the verge of the limitation. Only a few surface water samples had high concentration of NH4+and NO2-due to directly discharged of the sewage, while the concentration of NO3-were low. In this region,δ15N values of nitrates in groundwater ranged from 5‰~25‰, and the values ofδ18O ranged from 5‰~10‰, indicating that nitrate source of the groundwater were livestock excrement and living sewage, and also probability of fertilizer and soil organic nitrogen-mixing. At the same time, isotope fractionation generated by microbial nitrification couldn’t be ignored. N and O isotope ratios in part of the sample points were in the range of 1.3~2.1, while another part of the samples were not within this range, indicating that the denitrification was not distinct in the groundwater, and it had spatial heterogeneity.%为确定桂林东区岩溶含水层氮污染特征及其迁移转化过程,选择桂林东区地下水与地表水共27个采样点,分别在雨季和旱季进行取样分析.结果显示：桂林东区地下水NO3--N污染较严重,是最主要的无机氮形态.雨季地下水采样点的NO3--N平均浓度为12.5mg/L,超过了世界卫生组织的地下水饮用标准界限(10mg/L)；旱季地下水采样点的NO3--N平均含量为8.8mg/L,虽有明显的降低,但也濒临超标.而少数地表水采样点由于受到直接排污影响,NH4+和NO2-浓度较高,其余离子浓度均较低.该区地下水中硝酸盐的δ15N值范围在5‰~25‰,δ18O值范围在5‰~10‰,表明该区地下水硝酸盐来源为家畜粪便和生活污水,也可能有土壤有机氮和化肥的混合,并发生微生物的硝化作用产生同位素分馏.其中一部分采样点NO3-的N、O同位素比值在1.3~2.1的变化范围内,而另有一部分采样点NO3-的N、O同位素比值不在这个范围之内,表明该区地下水中反硝化作用并不明显,存在空间差异性.
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