氮同位素技术的应用:土壤有机氮作为地下水硝酸盐污染源的条件分析

在土壤排水良好、氧化的地下水环境中,地下水的氮同位素组成反映了源的特征。当地下水硝酸盐的δ15N值在+4‰～+9‰范围内时,这个值域指示地下水硝酸盐污染源是土壤有机氮或化肥与粪便的混合。通过分析对比前人研究资料,地下水中硝酸盐是否来自土壤有机氮的转化,其前提条件是研究区土壤有机氮是否丰富,特别是包气带中是否积累了大量有机氮转化的NO3-,并以石家庄市地下水硝酸盐污染为例,说明了这种条件分析在氮同位素技术应用时的重要性。通过包气带岩性、有机质和NO3-含量分析、施肥区与未施肥区灌水试验对比,土壤有机氮不是石家庄市地下水NO3-的一个主要污染源。当地下水硝酸盐低浓度时(1991),85.7%的样品NO3-的δ15N值在+6.1‰～+8.4‰范围内,指示污染源主要为化肥与粪便的混合,而当现今的高浓度时,样品硝酸盐的δ15N均值(+9.9‰±4.4‰)大于+8‰和超过半数(65%)样品的δ15N值大于+8‰,指示污染源主要是粪便或含粪便的污水。     

含氮污水灌溉实验研究及污染风险分析

在野外实验基地进行的含氮污水灌溉实验工作基础上,分析了污灌过程中氮化合物在土壤及地下水中迁移转化规律.研究结果表明,污灌对下层土壤及地下水中NH₄+浓度影响较小,但对NO₃-浓度影响较大,尤其是长期进行污灌的土壤,易造成地下水中NO₃-污染.利用本文推导的数学模型,可以定量预测污水灌溉后土壤水及地下水中NH₄+、NO₃-浓度的时空变化.采用Monte-Carlo法,进行含氮污水灌溉污染风险分析,结果表明,进入地下水的NO₃--N最大浓度超过污灌水NO₃--N浓度0.76倍的可能性为25%、超过污灌水NO₃--N浓度0.43倍的可能性为75%,污灌造成的地下水NO₃-污染风险必须引起注意.     

环境氮同位素方法示踪石家庄市地下水中硝酸盐来源

石家庄市地下水中硝酸盐含量呈上升趋势，水中硝酸盐含量分布范围为（0.4-96.0）×10-6，均值28.4×10-6，其δ15N值分布范围+6.1‰—+8.4‰，在地下水水位降落漏斗中心区（面积约8km2）δ15N值大于+9.6‰，表明有来自动物粪例的污染，其余地区水中硝酸盐的δ15N值介于+6.1‰—8.4‰之间，均值+6.9‰，表明该硝酸盐来自土壤有机氮     

漓江流域碳氮同位素组成特征及其来源初探

以漓江流域境内地表河和地下河为研究对象，通过测定、分析水体中的水化学组成以及δ13C_DIC、δ15N-NO₃-、δ18O-NO₃-等，利用同位素质量平衡混合模型，初步探讨了漓江流域境内DIC、硝酸盐的分布特征及其来源.结果表明:漓江流域DIC（即HCO₃-）浓度和无机碳稳定同位素（δ13C_DIC）分别在12.20~402.60 mg·L-1和-17.29‰~-10.01‰，平均值分别为140.3 mg·L-1和-13.06‰.NO₃-浓度在2.37~35.38 mg·L-1，δ15N-NO₃-在0.99‰~11.09‰，均展现出明显的空间变异特征.有机肥和污水对漓江流域硝酸盐的贡献最为显著，贡献比达57.00%.其次是化肥、降雨中的NH₄+和土壤N，贡献比分别是36.45%，6.55%.流域内DIC主要来源于碳酸盐岩的风化和土壤CO₂的溶解，同时也受硝酸溶蚀碳酸盐岩和大气CO₂的影响.结果可为定制有效的控制硝酸盐的输入途径，净化水质测略提供依据.      

污水灌溉土壤及地下水三氮的变化动态分析

取徐州奎河的生活污水进行饱和灌溉实验,由埋设在田间的一对蒸渗仪(地下水位保持在1m)观测,结果表明:污水中含量高达5035mg/L的氨氮进入土壤后,大部分被土壤胶体所吸附,迁移能力差,一般不会直接污染地下水。但污水在下渗时,能淋溶土壤中积存的NO₂-和NO₃-离子,使它们在地下水中的含量迅速增加。污灌以后,随土壤含水量、氧化还原电位和Ph值的变化,氨化作用、硝化作用和反硝化作用依次成为氮素转化的主要机制。污灌10d之内,由于淋溶和硝化作用产生的NO₂-、NO₃-会造成浅层地下水的严重污染。     

桂林甑皮岩岩溶地下水硝酸盐来源与转化

峰林平原是人类活动和居住的密集区，也是岩溶地下水系统的主要径流、排泄地段，地下水资源丰富。随着城市化的发展，地下水硝酸盐污染问题日渐突出。为研究桂林甑皮岩岩溶地下水硝酸盐来源与转化，分别于2018年10月、2019年2月、3月和4月采集地下水样，利用常规水化学及氮氧同位素技术识别硝酸盐来源与转化。结果表明:甑皮岩地下水中NO3-浓度在0~19.523 mg?L-1，δ15N-NO3-和δ18O-NO3-分别在-0.17‰～45.12‰和-5.82‰~16.47‰。硝酸盐氮氧同位素数据表明，甑皮岩地下水硝酸盐来源主要为粪便及污废水，少量来自降雨中的NH4+和土壤有机氮。受岩溶介质不均一性的控制，甑皮岩地下水中NO3-浓度、δ15N-NO3-和δ18O-NO3-均表现出明显的空间变异性。甑皮岩地下水硝酸盐的转化过程复杂，受控于季节和岩溶介质不均一性，表现为旱季以反硝化为主，雨季则以硝化过程为主。厘清硝酸盐来源与转化为治理甑皮岩地下水硝酸盐污染提供一定的科学依据。      

东阿水文地质单元地下水硝酸盐污染来源的同位素分析

针对近年来地下水硝酸盐污染日益严重的现象,本文运用氮同位素技术对位于典型农业区的东阿水文地质单元地下水氮污染来源进行了研究,结果表明:浅层地下水监测点的NO3-含量较高,平均含量为27.77 mg·L-1 ,δ15N 为7.8‰~12‰,反映了浅层地下水主要受到生活污水或粪便的污染;深层地下水（岩溶水）中NO3- 含量相对较低,平均含量为12.81 mg·L-1,δ15N为7.2‰~14.3‰,同样指示为生活污水或粪便污染,与补给区人为干扰密切相关。部分监测点地下水质量较差,建议研究区内使用高效的灌溉技术及科学的施肥方式,补给区附近的家禽养殖场可通过修建发酵池和改善饲料配方等方式,从源头上降低地下水硝酸盐的输入量。      

利用氮同位素技术识别石家庄市地下水硝酸盐污染源

地下水NO－ 3污染是石家庄市地下水管理面临的一个主要问题。本次研究通过地下水及其潜在补给源的氮同位素和水化学调查，确定和识别石家庄市地下水NO－ 3污染程度和污染源。地下水中的无机氮化合物主要以NO－ 3形式存在，浓度变化在 2．65～152．1 m g／L之间，均值为（54．88± 31）m g／L（ n＝44），48％的样品浓度超过国际饮水标准（50 m g／L）。地下水样品的NO－ 3－ 15 N值域＋4．53‰～＋25．36‰，均值＋9．94‰±4．40‰（ n＝34）。34个样品中，22个样品（65％）的氮同位素值大于＋8‰；与1991年相比，氮同位素组成指示地下水NO－ 3的主要来源已由当时矿化的土壤有机氮变为现在的动物粪便或污水；结合Cl－分析，南部地下水NO－3还受到东明渠污水的影响。其余12个样品（35％）的氮同位素值变化在＋4‰～＋8‰之间，其中 15 N值较大的（＋6‰～＋8‰）指示来自土壤有机氮，较小的（＋4‰～＋6‰）指示来自氨挥发较弱、快速入渗的化肥厂污水。根据上述研究结果，提出了改善石家庄市地下水管理的措施。     

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

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。     

广州夏季雨水硝酸盐δ15N变化特征

通过对广州2007年夏季雨水硝酸盐δ15的研究,讨论了广州地区雨水硝酸盐的主要来源及与之有关的大气化学演变过程。雨水硝酸盐占δ15N的变化趋势与N2O5含量的相似。暗示雨水硝酸盐δ15N与氮氧化合物的大气化学过程之间存在某种联系。白天雨水硝酸盐δ15N值偏低,与OH自由基氧化NOx生成硝酸盐的“白天反应”为主要反应相一致;18：00以后硝酸盐δ15N值呈升高趋势,则与N2O5累积的“夜间反应”成为主导反应相一致。因“白天反应”生成的HNO3的δ15N值受同位素分馏影响较小,白天雨水硝酸盐占δ15N值更能准确反映大气NOx的来源。白天雨水硝酸盐占δ15N平均值为2．5‰±2．1‰,表明除火力发电厂和机动车尾气排放来源外,雷电以及海源对大气NOx可能也有潜在贡献。     

Nitrogen isotope studies of nitrate contamination of the thick vadose zones in the wastewater-irrigated area

The objective of this study was to investigate natural abundance and the distribution of nitrogen isotopic compositions to assess denitrification in two ~30 m thick vadose zones beneath the different land uses in the wastewater-irrigated area located in southern Shijiazhuang, China. Sediment samples were collected from cores of boreholes drilled in the vegetable growth plot and the wastewater-irrigated farmland for analyses of nitrogen isotopes, physical and chemical properties, respectively. The profile of borehole A drilled in the vegetable growth plot only applied animal wastes had lower δ¹⁵N values of mean +7.5 ‰ in the upper vadose zone, but higher values of mean +10.9 ‰ in the lower vadose zone. δ¹⁵N values in each part varied little with depth, indicating no or little denitrification occurred in the deep vadose zone below the soil zone. The profile of borehole B drilled in the wastewater-irrigated farmland had low δ¹⁵N values of mean +5.7 ‰ below the soil zone and little variations of δ¹⁵N values with depth, indicating no or little denitrification occurred in the deep vadose zone below the soil zone. This was also verified by consistent variations of NO₃ ^? and SO₄ ^2? contents with Cl^? contents. Our results suggested most of leachable nitrate from the soil zone was hardly subjected to biological attenuation into groundwater.     

N-15 Identification of nonpoint sources of nitrate contamination beneath cropland in the Nebraska Panhandle: two case studies

Monitoring of municipal wells near the town of Sidney and domestic wells near Oshkosh in Nebraska's Panhandle indicated the nitrate-nitrogen (NO₃-N) levels were increasing and exceeded the maximum contaminant level of 10 mg/l NO₃-N in several wells. Both areas are located in narrow stream valleys that are characterized by well-drained soils, highly permeable intermediate vadose zones, shallow depths to groundwater, and intensive irrigated corn production. Both areas also have a large confined cattle feeding operation near the suspected contamination and potentially could be contaminated by more than on nitrate source.At Sidney NO₃-N concentrations were measured in 13 monitoring wells installed along an east-west transect im the direction of groundwater flow, 26 private wells, and eight municipal wells. Nitrate-nitrogen concentrations were homogeneous beneath a 5 km by 1.2 km area and averaged 11.3 ± 1.8 mg/l NO₃-N. The δ¹⁵N-NO₃ values in the monitoring and municipal wells had a narrow range from +5.8 to +8.8%. The isotopic ratios are indicative of a mixed source of nitrate contamination, which originates from agronomic (commercial fertilizer N and mineralized N) N and animal waste. Both commercial fertilizer N and animal wastes are applied to the irrigated fields.Nitrate-nitrogen concentrations in two multilevel samplers installed downgradient from irrigated cornfields at the Oshkosh site averaged 20.1 ± 13.3 mg/l NO₃-N and 37.3 ± 8.2 mg/l NO₃-N. The δ¹⁵N-NO₃ values spanned a narrow range from +3.5 to +5.9% and averaged +4.0 ± 0.5% and +5.0 ± 0.6%. These low values are indicative of leachates from commercial fertilizer applied to the irrigated fields.     

招远金矿区水体中硫同位素特征及其对污染来源的指示

稳定同位素因其指纹效应已成为分析矿区污染来源的重要技术手段。文章以招远金矿区为例,应用硫同位素联合水化学分析、聚类分析及氢氧同位素分析招远金矿区水污染特征和成因。通过分析可知,矿区内地表水和地下水主要接受大气降水补给,水力联系密切。水化学类型以SO₄—Ca和SO₄—Na型为主,阴离子以SO₄2-为主,地表水和地下水的NO₃-和Cl-在空间上变异性较大。地表水硫酸盐含量普遍偏高,硫酸盐污染较为严重,高值区出现在玲珑金矿、金翅岭金矿和张星镇附近;而地下水高值区都出现在玲珑金矿附近,且SO₄2-浓度沿着径流方向逐渐降低。地表水中硫酸盐δ34S值介于1.8‰~9.8‰,地下水中硫酸盐δ34S值介于2.7‰~9.6‰,地表水和地下水硫酸盐含量受玲珑金矿硫化、玲珑花岗岩和胶东岩群影响明显。在地下水径流途中,有地表水入渗污染地下水的现象。另外,工业废水的排放也是硫酸盐含量升高的主要原因。研究表明:硫同位素在金矿区硫酸盐污染的来源和特征方面有很好的指示作用,是评价矿山开采对地下水污染的有效工具。     

岩溶裂隙含水层中石油类有机物的自然衰减机制

石油类有机物污染是地下水环境领域亟须解决的关键课题.本次研究耦合数值模拟和水文地球化学技术模拟岩溶裂隙含水层中石油类有机物的自然衰减过程并定量计算其自然衰减机制.基于BIOSCREEN模型的模拟计算可知,近30年对流、弥散、稀释等物理过程和生物降解过程对石油类有机物衰减贡献率的平均值分别为31.53%和68.47%,生物降解作用是岩溶裂隙含水层自然修复能力的主要机制.利用质量守恒定律分析水化学（HCO₃-、NO₃-）和同位素（δ15N_NO3、δ18O_NO3和δ13C_DIC）之间的相关关系可知石油类有机物生物降解贡献地下水HCO₃-的平均值为33.93%;石油类有机物生物降解消耗主要电子受体NO₃-贡献地下水δ13C_DIC的百分率为30.77%且其占总生物降解的90.69%.      

沁水盆地南部潘庄区块废弃矿井煤层气地球化学特征及成因

为了研究废弃矿井中煤层气成因,以沁水盆地南部潘庄区块废弃矿井为例,抽采废弃矿井中煤层气并进行化学组分和同位素测试,并采集部分废弃矿井水样品测试水中离子浓度、pH值等进行研究。结果表明:潘庄区块废弃矿井中煤层气CH₄体积分数平均值为91.99%,CO₂为1.26%,N₂为6.73%;甲烷碳同位素（δ13C₁）值为-31.36‰~-33.53‰,平均-32.25‰,氢同位素（δD）值为-182.76‰~-193.20‰,平均-187.538‰。废弃矿井排采水中阴阳离子主要为Mg2+、K+、HCO₃-、Cl-、Na+、SO₄2-和NO₃-等,产出水型为Mg-（HCO₃）₂型,表明矿井水受到地表水的强烈影响。废弃矿井中煤层气主要以热成因气为主,少量次生生物气。与附近未开采煤储层相比,研究区废弃矿井中的环境更有利于次生生物气的生成。      

Isotope analysis of nitrate pollution sources in groundwater of Dong'e geohydrological unit

As nitrate pollution in groundwater has become increasingly serious in recent years, nitrogen isotope was adopted in this paper to define its sources in a typical agricultural area of Dong'e hydrogeological unit. The results show that: Higher content of NO_3~- detected in shallow groundwater is 27.77 mg/L on average and δ15 N content ranges from 7.8‰ to 12 ‰, indicating that shallow groundwater is mainly contaminated by sewage or feces. In contrast, less NO_3~- in deep groundwater(karst water) has an average value of 12.81 mg/L and δ15 N content is between 7.2‰ and 14.3‰, which is closely related to human disturbance as mentioned above. In addition, considering relatively low groundwater quality at some monitoring sites, reasonable fertilization is a better choice in the study area to reduce nitrate source in groundwater.     

Isotope analysis of nitrate pollution sources in groundwater of Dong’e geohydrological unit

As nitrate pollution in groundwater has become increasingly serious in recent years, nitrogen isotope was adopted in this paper to define its sources in a typical agricultural area of Dong’e hydrogeological unit. The results show that: Higher content of NO3- detected in shallow groundwater is 27.77 mg/L on average and δ15N content ranges from 7.8‰ to 12 ‰, indicating that shallow groundwater is mainly contaminated by sewage or feces. In contrast, less NO3- in deep groundwater (karst water) has an average value of 12.81 mg/L and δ15N content is between 7.2‰ and 14.3‰, which is closely related to human disturbance as mentioned above. In addition, considering relatively low groundwater quality at some monitoring sites, reasonable fertilization is a better choice in the study area to reduce nitrate source in groundwater.     

Application of multiple-isotope and groundwater-age data to identify factors affecting the extent of denitrification in a shallow aquifer near a river in South Korea

The extent of denitrification in a small agricultural area near a river in Yangpyeong, South Korea, was determined using multiple isotopes, groundwater age, and physicochemical data for groundwater. The shallow groundwater at one monitoring site had high concentrations of NO₃-N (74–83 mg L^?1). The δ¹⁵N-NO₃ values for groundwater in the study area ranged between +9.1 and +24.6‰ in June 2014 and +12.2 to +21.6‰ in October 2014. High δ¹⁵N-NO₃ values (+10.7 to +12.5‰) in both sampling periods indicated that the high concentrations of nitrate in the groundwater originated from application of organic fertilizers and manure. In the northern part of the study area, some groundwater samples showed elevated δ¹⁵N-NO₃ and δ¹⁸O-NO₃ values, which suggest that nitrate was removed from the groundwater via denitrification, with N isotope enrichment factors ranging between ?4.8 and ?7.9‰ and O isotope enrichment factors varying between ?3.8 and ?4.9‰. Similar δD and δ¹⁸O values of the surface water and groundwater in the south appear to indicate that groundwater in that area was affected by surface-water infiltration. The mean residence times (MRTs) of groundwater showed younger ages in the south (10–20 years) than in the north (20–30 years). Hence, it was concluded that denitrification processes under anaerobic conditions with longer groundwater MRT in the northern part of the study area removed considerable amounts of nitrate. This study demonstrates that multi-isotope data combined with physicochemical data and age-dating information can be effectively applied to characterize nitrate contaminant sources and attenuation processes.