【作者】 刘超；

【导师】 陈鸿汉； 何江涛；

【作者基本信息】 中国地质大学（北京） ， 地下水科学与工程， 2011， 硕士

【摘要】 地下水氮污染问题一直是广泛受到关注的问题,而包气带岩性、结构、厚度等在很大程度上影响氮污染物的入渗和降解,进而决定着地下水是否易受到污染及其污染程度。本文针对浅层地下水铵态氮污染较为严重的北京市东郊温榆河沿岸地区,通过一系列钻孔剖面,揭示了区内包气带中氮素的垂向分布特征;以含有细质地透镜体,粗细交错的非均质包气带结构为对象,通过室内砂箱模拟实验,就恒定模拟降雨强度下砂箱中水分运移、铵态氮污染及淋溶过程中氮素的迁移转化和富集分布规律进行了研究,主要得出以下结论:(1)钻孔氮素垂向分布特征研究表明,研究区9个钻孔铵态氮底部出现累积峰;硝态氮主要表现为表层(30cm)累积和中部含量高的单峰型两种分布类型;氮素分布与岩性无明显相关关系,推测可能是由于包气带粗细分层相互交错的结构影响了地表氮污染物在包气带中的迁移过程最终导致其分布的复杂化。(2)水分运移实验结果表明,粗细相间的非均质介质中存在水分绕流现象,粗细介质颗粒粒径差距越大,水分绕流越明显;同细砂层相比,亚粘土透镜体中含水率高达29%,说明亚粘土透镜体对水分的滞留能力大于细砂层;铵态氮连续穿透实验结果亦表明质地细密的亚粘土透镜体中铵态氮累积量较高,亚粘土透镜体对铵态氮和水分的滞留能力大于质地较粗的细砂层。(3)铵态氮间歇污染实验表明,历时23个周期89天基本达到吸附-硝化反硝化-吸附的稳定状态。包气带氮素的迁移和分布受介质的非均匀性影响明显,同野外氮素分布规律相似,砂箱上层土壤中硝态氮累积较多,铵态氮和亚硝态氮在砂箱深层土壤中得到累积,同时在上亚粘土透镜体的上下表面土壤中出现较明显的铵态氮和亚硝态氮累积;淋溶试验结果表明,历时9个周期出水氮素含量减少90%,模拟降雨对土层残留氮素具有显著的淋洗效应,而亚粘土透镜体的存在可阻滞氮素的下移。(4)氮平衡计算结果表明:出水淋失总氮量占进入系统总氮量的70%,反硝化损失氮量占进入系统总氮量的17%;本实验条件下硝化反应强烈,反硝化作用相对较弱,大部分氮素以铵态氮、硝态氮和亚硝态氮的形态随出水淋失。更多还原

【Abstract】 Nitrogen pollution of groundwater has become a popular problem in the world, which has been posed a great risk to the drinking water supply. During the process of the contaminants infiltrate from land surface to the groundwater, the unsaturated zone soil texture, structure and thickness have large effects on the nitrogen transport and transformation, and then decide the possibility and degree of groundwater contamination. An area along Wenyu River was selected as the study area which is polluted to various extents of ammonium nitrogen in shallow groundwater. Soil samples were collected from a series of boreholes in unsaturated zone and the vertical distribution characters of nitrogen in the profiles were analyzed. Laboratory experiments with simulated rainfall were conducted using a sandbox to investigate the influence of unsaturated zone heterogeneous structure on the process of moisture transfer, nitrogen transport and transformation. The results were summarized as follows:(1) Vertical distribution characters of nitrogen in unsaturated zone profiles indicate that: An accumulation of ammonium nitrogen is found in the lower parts of 9 soil profiles in the study area; There are two main types of the residual nitrate nitrogen distribution: one was the accumulation of nitrate appeared in the surface soil, and the other was the peak value of nitrate concentration appeared in the middle of profile. The results have shown that no obvious relations between the distribution of nitrogen and the soil texture, which suggests that the soil strcture and layered-structure may have an effect on the nitrogen transport and transformation in the unsaturated zone and finally result in the complex of its distribution.(2) Experimental study on moisture transfer shows the preferential flow occurred in the heterogeneous unsaturated zone, and the difference between soil textures has great effect on preferential flow formation. Water content is 29% in the two clay lenses which suggests that the clay lenses keep more water than fine sand layer. Even in the breakthrough experiment, the distribution of ammonium nitrogen in the soil keeps the same characteristic with the soil water. Both experiments demonstrate that soil water and nitrogen are maintained at a higher level in the clay lenses.(3) Study on intermittent contamination of ammonium nitrogen reveals that the dynamic equilibrium of absorption and biodegradation is reached after 89 days. The unsaturated zone soil texture and layered-structure are very important to the nitrogen transport and transformation which lead to an accumulation of ammonium nitrogen and nitrite nitrogen in the upper surface of two sandy-clay interface. Nitrate nitrogen is accumulated in the topsoil while an accumulation of ammonium nitrogen and nitrite nitrogen is found in the sublayer soil. The leaching test suggests that nitrogen concentration in outflow were reduced more than 90 percent after 9 periods. Stimulated rainfall has a significantly effect on the leaching of nitrogen while the clay lenses can retard the transport of nitrogen.(4) In a study of nitrogen balance, it is found that total leaching losses of nitrogen and denitrification loss account for 70% and 17% respectively; It is also suggested that nitrification is intensity high and denitrification is comparatively weak in the simulated sandbox; Most of nitrogen is lost in outflow water in the forms of ammonium, nitrate and nitrite nitrogen.更多还原