Analysis of nitrate sources in surface water in northern Yantai based on nitrogen and oxygen isotopes and MixSIAR model
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摘要:
研究目的 地表水硝酸盐污染是全世界关注的一个环境问题，因此识别硝酸盐的来源和转化是改善水质的基础。
研究方法 为准确识别烟台北部地表水硝酸盐来源及转化过程，利用水化学方法及硝酸盐氮氧双同位素技术，对烟台北部大沽夹河、辛安河、沁水河、汉河等不同流域地表水进行采样分析，并结合贝叶斯同位素混合模型MixSIAR对各硝酸盐来源贡献率进行计算。
研究结果 （1）研究区地表水呈弱碱性，NO3−−N浓度远高于NH4+−N和NO2−−N浓度，为研究区地表水主要氮素污染物，仅辛安河NO3−−N浓度符合国家规定的生活饮用水卫生标准限值10 mg/L；（2）研究区地表水硝酸盐转化过程以硝化作用为主，反硝化作用不明显；（3）MixSIAR模型输出结果显示，研究区地表水各硝酸盐源的贡献率依次为污水粪肥（51.1%）>土壤有机氮（23.9%）>化肥（22.9%）>大气沉降（2.1%）。
结论 总体上，研究区地表水硝酸盐来源以污水粪肥贡献率最大，其次是土壤有机氮和化肥。人为输入产生的污水粪肥是研究区硝酸盐污染的主要来源，因此减少污水粪肥对各河流的排放是控制污染的关键。
Abstract:This paper is the result of environmental geological survey engineering.
Objective Nitrate pollution in surface water is a global environmental issue, therefore identifying the source and transformation of nitrate is fundamental to improving water quality.
Methods To accurately identify the sources and transformation processes of nitrate in surface water in north of Yantai city, hydrochemistry and dual isotopes of nitrate nitrogen−oxygen technologies were used to sample and analyze surface water from different river basins, including Dagujia River, Xin'an River, Qinshui River, and Han River. And the Bayesian isotopes mixing model MixSIAR was also used to calculate the contribution rates of various nitrate sources.
Results (1) The surface water in the study area is weakly alkaline, with NO3−−N concentration significantly higher than NH4+−N and NO2−−N concentrations, making NO3−−N is the primary nitrogen pollutant in the surface water of the study area. Only the NO3−−N concentration in Xin'an River (NO3−−N<10 mg/L) fell within the national health standard for drinking water. (2) Nitrification dominates the nitrate transformation process in the surface waters in the study area, while denitrification playing a negligible role. (3) The output results of the MixSIAR model show that the contribution rates of nitrate sources in surface water in the study area are as follows: sewage and manure (51.1%)>soil organic nitrogen (23.9%)>chemical fertilizer (22.9%)>atmospheric deposition (2.1%).
Conclusions Overall, sewage and manure have the highest contribution rate to nitrate sources in surface water in the study area, followed by soil organic nitrogen and chemical fertilizer. Sewage and manure from anthropogenic inputs are the main sources of nitrate pollution in the study area. Therefore, reducing discharge of sewage and manure into rivers is key to controlling pollution.
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表 1 烟台北部地表水水化学参数及硝酸盐氮氧同位素组成
Table 1. Chemical parameters and nitrate isotopes of surface water in study area
河流 范围 pH TDS CODcr HCO3− SO42− Cl− Ca2+ Na+ Mg2+ K+ (NO3−−N) (NH4+−N) (NO2−−N) (δ15N−NO3−) (δ18O−NO3−) 大沽夹河
（n=12）最大值 9.2 254.0 8.00 292.0 114.0 72.6 138.0 61.1 40.0 9.37 64.7 0.363 1.530 16.81 10.54 最小值 7.5 54.0 0.80 69.8 74.0 26.3 37.6 31.4 13.3 3.07 9.7 0.009 0.081 11.17 6.49 中位数 8.8 91.5 4.90 112.5 90.1 44.9 49.0 37.2 18.5 7.13 29.4 0.085 0.495 13.79 7.77 平均值 8.6 136.3 4.70 126.9 89.5 45.1 59.7 39.0 20.4 7.01 30.1 0.118 0.593 14.32 8.04 标准差 0.5 74.8 2.19 56.7 10.9 14.1 28.5 7.6 6.4 2.0 17.3 0.100 0.480 1.80 1.09 辛安河
（n=4）最大值 8.6 79.0 6.72 162.0 93.7 53.1 116.0 44.9 22.1 9.0 6.8 0.113 1.910 22.47 12.96 最小值 8.1 20.0 3.04 133.0 26.5 26.5 40.2 27.4 13.8 4.1 2.6 0.017 0.080 14.69 8.35 中位数 8.2 50.5 3.40 149.0 93.2 52.0 47.5 41.3 21.0 4.7 3.8 0.030 0.118 15.02 9.81 平均值 8.3 50.0 4.14 148.3 76.7 45.9 62.8 38.7 19.5 5.6 4.3 0.047 0.556 16.80 10.23 标准差 0.2 23.6 1.50 13.8 29.0 11.2 30.9 6.8 3.3 2.0 1.6 0.039 0.780 3.28 1.69 沁水河
（n=7）最大值 7.8 71.0 4.64 140.0 72.8 29.5 48.0 36.5 14.9 9.3 33.5 0.271 1.430 14.23 6.58 最小值 7.1 24.0 1.12 69.8 45.6 21.2 30.2 26.0 9.5 5.4 9.8 0.021 0.072 8.32 5.15 中位数 7.5 59.0 3.68 117.0 58.9 26.0 38.3 31.9 12.4 6.4 16.0 0.119 0.108 12.61 5.63 平均值 7.5 55.3 3.52 114.1 60.0 26.3 38.8 32.3 12.5 6.8 16.8 0.112 0.306 11.79 5.88 标准差 0.2 13.8 1.03 20.1 8.5 2.8 5.6 3.2 1.7 1.2 7.2 0.077 0.461 1.87 0.47 汉河
（n=5）最大值 7.93 852.0 4.80 152.0 1701.0 13115.0 402.0 4811.0 955.0 394.0 25.8 0.180 1.430 22.67 18.21 最小值 7.47 67.0 0.32 44.4 16.3 11.2 14.5 12.8 5.0 2.9 4.1 0.060 0.089 12.20 5.96 中位数 7.86 190.5 2.40 98.4 69.4 28.7 76.9 45.0 14.6 5.7 22.9 0.110 0.488 13.36 7.03 平均值 7.74 325.0 2.40 99.0 393.0 2714.7 122.5 1039.0 204.7 85.7 17.0 0.120 0.587 15.27 9.05 标准差 0.19 308.4 1.43 34.1 654.7 5202.2 142.4 1888.7 375.3 154.3 9.1 0.044 0.457 3.79 4.60 注：pH无量纲，(δ15N−NO3−)、(δ18O−NO3−) 单位为‰，其余单位为mg/L。 
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表 2 硝酸盐来源氮、氧同位素组成
Table 2. Summary of the δ15N−NO3− and δ18O−NO3− values of various nitrate sources
来源 δ15N−NO3− δ18O−NO3− 文献 平均值±标准偏差 平均值±标准偏差 大气沉降 4.6±3.9 54±13.2 Ren et al., 2024 化肥 0.9±2.0 3.0±1.4 Mu et al., 2024 土壤有机氮 3.8±1.8 −2.7±4.4 Zhang et al., 2022 污水粪肥 11.5±1.2 5.6±1.4 Chen et al., 2023
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