硝酸盐污染氮氧同位素溯源及贡献率分析——以南阳地区为例

Using isotopes of nitrogen and oxygen to trace groundwater nitrate contamination and contribution analysis: exemplified by the Nanyang District

南阳盆地地下水硝酸盐污染形势不容乐观,但是其成因尚不清楚。为了识别该地区浅层地下水中硝酸盐的污染来源,系统采集了28组样品,基于稳定同位素质量守恒定律和线性混合定律,通过分析硝酸盐中氮氧同位素组成(δ15N、δ18O),定量计算出了不同污染源对地下水硝酸盐的贡献程度。研究结果表明:该地区浅层含水层地下水NO-3-N的浓度均值为23.25 mg/L,以地下水质量Ⅲ类水为标准,超标率达39.29%;污水及粪便是造成硝酸盐污染的主要原因,其平均贡献率为73%;其次为化肥的施用占23%;该地区地下水环境受人类活动影响强烈,而自然因素对硝酸盐污染的贡献程度可忽略不计。

Early researches show that the shallow aquifer of the Nanyang district,at which the South to North Water Diversion Project starts,has been contaminated by nitrate.In this study,28 groups of shallow groundwater samples are collected.By measurements of nitrogen and oxygen isotopes(δ15 N and δ18 O),combined with the linear mixing model based on the mass conservation law of stable isotopes,the quantitative results of the potential sources of nitrate contamination are obtained.The results show that the average concentration of NO3-N in shallow groundwater is 23.25 mg/L and 39.29% of all the samples are above the level Ⅲ of the Groundwater Quality Standard.The data from all the samples indicate the sewage and manure are the main reason of the nitrate pollution in the study area,which account for 73% of the overall level.The use of fertilizer is the secondary cause,which takes up 23%,and the natural factors are negligible compared to the anthropogenic activities.