湖南安乡地下水污染（氨）的成因研究

RESEARCH ON THE FORMATION OF GROUNDWATER AMMONIA NITROGEN POLLUTION IN ANXIANG, HUNAN PROVINCE

黄燕鹏

11649179

硕士

环境工程

胡清

2018-05-29

2018-07-09

哈尔滨工业大学

深圳

安乡县位于湖南省北部、洞庭湖西北部，是常德市下辖行政县。近年来，因地表水水质恶化，县政府自2005 年起陆续修建地下水水源水厂共37 座，供给农村居民生活使用。因此，县内农村居民对地下水具有较高的依赖性。但区域的地下水中存在较大程度的氨氮污染，大部分区域氨氮浓度超过《地下水质量标准》（GB/T 14848-93）中规定的Ⅴ类水标准。为保障县内农村居民安全饮水，其地下水氨氮污染的成因研究急需开展。本研究依托于湖南省水污染防治专项“安乡县地下水资源保护区划”项目。通过现场调研、采样与分析、自然环境与水文地质资料、历史水质监测数据等资料的收集与分析等工作，结合地下水水化学、环境同位素、地统计学与数理统计学等方法，探讨了安乡县地下水中氨氮污染的形成原因。主要研究成果如下：（1）根据2017 年分析检测的结果，研究区地下水的氨氮污染呈现由西北往东南方向氨氮浓度逐渐增加的空间分布。结合2005 年以来的监测数据，利用氨氮年增长速率与年增长倍数来评估氨氮的时间变化，发现研究区地下水的平均年增长速率为0.16mg/L，增长倍数为1.30。全县地下水的氨氮污染呈现逐渐加重的趋势；（2）地下水中八大离子的组成与TDS 浓度的分布揭示了区域地下水化学类型由岩石风化作用形成。结合氨氮与Ca2+、Mg2+、HCO3-等地下水主要离子的相关性分析，发现氨氮源于人为来源而非天然来源。（3）中性偏弱碱性的还原环境使得研究区地下水中发生的硝化作用较弱，这一点也被NO2-、NO3-的低含量所证明。这一结果使得无机氮组分以氨氮为主要形式存在。（4）氢氧同位素分析的结果与地下水等水位线等分析说明研究区地下水受到区域内的降水、地表水的补给，良好的水文条件为污染物的进入迁移增加了可能性。（5）氮同位素的分析证明化肥是研究区地下水氨氮污染的最终来源。研究区的氨氮污染程度与周边农田面积的正相关同样证明了农业（渔业）活动造成了研究区地下水氨氮污染。经估算，研究区每年因施肥流失氮量达到4.20×106 ～ 5.10×106kg。（6）根据成井资料分析，各水源井上覆隔水层厚度与水源井的氨氮浓度、氨氮年增长速率呈显著负相关（相关系数分别为-0.529，-0.577，检验值小于0.01）。进一步说明研究区地下水的氨氮有可能源自外源，通过隔水层往下迁移到达含水层。（7）由于NH4+在多孔介质中易被吸附（经计算，在每亩土地上，至少16m厚的粘土层的阳离子交换量达到5.13×109meq，远大于农田流失氮的总当量数2.75×105meq），且NO3-迁移性较强。因此，研究区地下水中的氨氮应是NH4+在土壤中被氧化为NO3-，再向下迁移至含水层中，受还原环境影响转化为NH4+导致，但有部分NH4+直接迁移至含水层的可能性仍然存在。（8）对研究区主要开采使用的含水层（双层承压层）进行含氨氮总量的估算，含水层中含氨氮总量为1.84×107kg，仅为（2）中估算的氮总量的3.61 ~4.38倍。可以预计，现有的施肥方式还会持续污染地下水。综上所述，研究区安乡县地下水中氨氮源于化肥入渗。降水、地表水与地下水的密切联系为氮素进入地下水提供了帮助。同时，地下水的中性偏弱碱性、还原环境促使无机氮组分以氨氮形式存在，造成地下水氨氮污染。

Anxiang County is located in the north of Hunan Province and northwest of Dongting Lake. It is an administrative county under the jurisdiction of Changde City. In recent years, due to the deterioration of surface water quality, the county government has successively built 37 groundwater source water plants since 2005 to provide rural residents with drinking water. Therefore, rural residents in the county have a high dependence on groundwater. However, there is a large degree of ammonia-nitrogen pollution in these groundwaters, and the concentration of ammonia nitrogen in most of the regions exceeds the V-type water standards specified in the Groundwater Quality Standard (GB/T 14848-93). In order to ensure safe drinking water for rural residents in the county, the research on the formation of ammonia nitrogen pollution in groundwater is urgently needed. This research is based on the "Anxiang County Groundwater Resources Protection and Zoning Plan" project from Hunan Province's special water pollution prevention and control project. It combines research, sampling and analysis, collection of natural environment and hydrogeological data, historical water quality monitoring data and analysis. Groundwater hydrochemistry, environmental isotopes, geostatistics, and mathematical statistics methods were used to discuss the formation of ammonia nitrogen pollution in groundwater in Anxiang County. The main research results are as follows:(1) According to the results of the analysis and testing in 2017, the ammonia nitrogen pollution of the groundwater in the study area shows a spatial distribution of increasing ammonia concentration from northwest to southeast. Combined with the monitoring data since 2005, the annual ammonia nitrogen rate was calculated by using the annual growth rate of ammonia nitrogen and the annual growth ratio. It was found that the average annual growth rate of groundwater in the study area was 0.16 mg/L, a growth multiple of 1.30, and ammonia nitrogen pollution in the whole county shows an increasing trend.(2) The composition of the eight major ions and the distribution of TDS concentration reveals that the regional groundwater is formed by the weathering of rocks. The analysis of the correlation between ammonia nitrogen and major groundwater ions such as Ca2+, Mg2+, and HCO3- shows that ammonia nitrogen originates from man-made sources rather than natural sources. .(3) The neutral and reducing environment makes the nitrification in groundwater in the study area weak, which is also proved by the low content of NO2- and NO3-. This result explains the reason why ammonia nitrogen is the main form of inorganic nitrogen in the groundwater.(4) The results of hydrogen and oxygen isotope analysis and groundwater and water level lines indicate that the groundwater in the study area is subject to precipitation and surface water recharge. Good hydrological condition increase s the possibility of pollutants entering and relocating.(5) The analysis of nitrogen isotopes proved that chemical fertilizer is the ultimate source of ammonia nitrogen pollution in the groundwater in the study area. The positive correlation between the degree of ammonia nitrogen pollution in the study area and the surrounding farmland area also proves that agricultural activities have caused ammonia nitrogen pollution in the groundwater in the study area. It has been estimated that the amount of nitrogen lost from fertilization in the study area will reach 4.20 × 106 to 5.10 × 106 kg per year.(6) According to analysis of well data, the thickness of overlying aquifers in each source well is significantly negatively correlated with the ammonia nitrogen concentration and the annual growth rate of ammonia nitrogen in the source wells (the correlation coefficients are -0.529, -0.577, and the test value is less than 0.01). The ammonia of groundwater in the study area may be derived from an external source and migrate through the aquifer down to the aquifer.(7) Since NH4+ is easily adsorbed in the formation (the cation exchange capacity of at least 16 m thick clay layer in each acre area reaches 5.13 × 109 meq, which is much larger than the total number of nitrogen lost in farmland 2.75 × 10 5 meq), and NO3- migration is strong, the ammonia nitrogen in the groundwater in the study area should be NH4+ in the soil is oxidized to NO3-, and then migrated down to the aquifer, and the reducing environment results in the conversion from NO3- to NH4+, but the possibility of NH4+ migrating directly into the aquifer remains.(8) Estimate the total ammonia-nitrogen content in the aquifer (bi-layer confined strata) mainly mined in the study area. The total content of ammonia -nitrogen in the aquifer is 1.84 × 107 kg, which is only 3.61 ~ 4.38 times larger than the nitrogen loss estimated in (2). It can be expected that the existing fertilization will continue to pollute groundwater.In summary, the ammonia nitrogen in the groundwater of the Anxiang County of the study area is derived from infiltration of chemical fertilizers. The close connection between precipitation, surface water and groundwater has helped the nitrogen to enter the groundwater. At the same time, the neutral and reducing environment of groundwater promotes the presence of inorganic nitrogen components in the form of ammonia nitrogen, resulting in ammonia nitrogen pollution of groundwater.

地下水 氨氮污染 成因 水化学 环境同位素

groundwater ammonia nitrogen pollution formation water chemistry environmental isotopes

中文

联合培养

哈尔滨工业大学

黄燕鹏. 湖南安乡地下水污染（氨）的成因研究[D]. 深圳. 哈尔滨工业大学,2018.