基于稳定同位素和贝叶斯模型的引黄灌区地下水硝酸盐污染源解析

Source identification of nitrate contamination of groundwater in Yellow River Irrigation Districts using stable isotopes and Bayesian model

地下水硝酸盐(NO_3^-)污染已经成为全球严重的水环境问题之一,由于饮用水中高含量NO_3^-会转化成亚硝酸盐而增加各种疾病和癌症风险,其来源的确定对于NO_3^-污染的预防和控制非常重要。本文以黄河下游第二大灌区——潘庄灌区为例,首次采用NO_3^-的氮氧稳定同位素结合贝叶斯模型追溯地下水NO_3^-的来源并量化各种来源的贡献比例。结果表明,地下水NO_3^-含量分布在0.1～197.0 mg·L^(-1),平均值为34.2 mg·L^(-1)。与《生活饮用水卫生标准》中规定的地下水NO_3^-最大含量[20 mg(N)·L-1,相当于NO_3^-含量90 mg·L^(-1)]相比,有10%的样品NO_3^-含量超标。井深<30m、30～60m和>60m的地下水NO_3^-平均含量分别为25.9mg·L^(-1)、39.7mg·L^(-1)和20.1 mg·L^(-1)。空间上,宁津县、武城县、平原县和禹城市有大片区域地下水NO_3^-含量较高。地下水NO_3^-的δ15N组成范围为0.72‰～23.93‰,平均值为11.62‰;δ18O组成范围为0.49‰～22.50‰,平均值为8.46‰。同位素结果表明粪便和污水、农业化肥是地下水中NO_3^-的主要污染来源。这反映了人类活动是引起地下水NO_3^-污染的主要原因。贝叶斯模型结果显示,粪便和污水对潘庄灌区地下水中NO_3^-平均贡献率高达56.2%,化肥的平均贡献率为19.3%,大气降水和土壤的平均贡献率分别为6.2%和12.3%。由于污水、粪便和化肥是地下水中NO_3^-的主要来源,为保护和改善研究区地下水水质,建议加强污水管道建设,强化畜禽粪便的管理以及提高化肥利用效率。

Nitrate(NO3-)pollution in groundwater has become a serious environmental problem across the world.It is very important to determine the sources of nitrogen contamination in order to prevent and control NO3-pollution in groundwater.This is because the intake of polluted water can increase health risk of methemoglobinemia and cancer in both aquatic lives and humans.There has been an in-creasing trend in NO3-pollution in groundwater in the Lower Yellow River Irrigation Districts.Once groundwater is polluted by NO3-,recovery efforts can be very daunting.The effective control and management of NO3-pollution require accurate identification of the actu-al sources of pollution.In this paper,the sources of NO3-in groundwater in the Lower Yellow River Irrigation District(Panzhuang Irri-gation District)were identified using stable isotopes(δ15N andδ18O)and the Bayesian model.The results showed that the range of NO3-concentrations in groundwater in the study area was 0.1–197.0 mg·L^-1,with a mean of 34.2 mg·L^-1.About 10%of the groundwater samples had NO3-concentration in excess of the maximal standard of nitrate level in drinking water in China(90 mg·L^-1).Samples were divided into three depths,including 0-30 m(shallow layer),30-60 m(middle layer)and>60 m(deep layer).The average NO3-concen-trations in shallow groundwater layer,middle layer and deep layer were 25.9 mg·L^-1,39.7 mg·L^-1 and 20.1 mg·L^-1,respectively.There were high NO3-concentrations in groundwater across Ningjin County,Wucheng County,Pingyuan County and Yucheng City.The composition ofδ15N was in the range of 0.72‰–23.93‰,with an average of 11.62‰.That ofδ18O was 0.49‰–22.50‰,with an av-erage of 8.46‰.The values ofδ15N andδ18O indicated that NO3-in groundwater in the study area mainly originated from chemical ferti-lizers,manure and sewage.The contributions of the four sources of NO3-(precipitation,chemical fertilizer,soil,manure and sewage)were quantified and estimated using the Bayesian model.The results showed that manure and sewage contributed the most to the overall NO3-level,with a mean NO3-contribution ratio of 56.2%.Chemical fertilizer was the second contributor,with a mean NO3-contribution ratio of 19.3%.The mean NO3-contribution ratio of precipitation and soil was 6.2%and 12.3%,respectively.After identification of NO3-pollution levels and sources,measures were required to reduce NO3-pollution in groundwater.Based on this study,the necessary measures included the construction of sewage pipeline and improving the utilization rate of chemical fertilizers in order to reduce NO3-pollution and improve water quality.