地下水硝酸盐污染是目前国际上亟待解决的地下水污染问题，本研究选取我国青岛市大沽河流域特色农耕蔬菜种植区域，为探究在同等入渗条件下农业施肥灌溉和生活污水排放对地下水硝酸盐氮浓度升高造成的影响，选取了研究区三种代表性土壤（分别命名为土壤A、土壤B、土壤C），通过批实验、一维土柱模拟实验及模型迁移验证模拟，测定了研究区域土壤基本理化性质、包气带土壤水动力条件和氮素本底值等，探究土壤不同环境条件对氮素转化的影响。将铵态氮和硝酸盐氮作为主要研究对象，探究土壤溶液pH、土壤盐度、土壤含水量、初始氮源浓度及土壤分层方式对二者转化与迁移的影响，能够为防控地下水硝酸盐污染提供更有针对性的建议。主要结论如下：

     （1）通过开展氮素转化的批次实验，结果表明：土壤中铵态氮只有在有氧情况下才发生硝化反应。土壤中含氧量或底物浓度升高，能促进硝化反应的发生；当土壤含水率低于10%时，会对氮素转化产生滞后影响，并降低氮素发生转化的比例；当土壤含水率高于10%时，硝化作用发生的时间会随着含水量的增高稍微延迟，但铵态氮的转化量不会降低；土壤中铵态氮不会全部参与硝化反应，而参与的部分全部转化为硝酸盐氮；以葡萄糖作为硝酸盐氮反硝化反应的碳源时，反硝化程度与土壤碳氮比呈正比。

    （2）通过批次试验测定土壤A、B、C吸附铵态氮及硝酸盐氮的过程，发现对数型及准二级动力学方程能够更好的拟合铵态氮及硝酸盐氮动力学吸附过程，Freundlich和Langmuir吸附模型能够更好的拟合二者等温吸附的过程。随着土壤溶液pH或NaCl浓度的减小，土壤对铵态氮的吸附量逐渐增大；土壤对硝酸盐氮的吸附量随溶液pH值的增大呈现先减小再增大的趋势，而受到NaCl浓度的影响较小。铵态氮在分层土壤中整体阻滞系数与各分层土壤厚度比和单一土壤的阻滞系数呈线性加和关系；在分层土壤干容重相差较小时，分层土壤分配系数与厚度的线性叠加关系能够很好的描述分层土壤等效分配系数与单一土层分配系数的关系。

    （3）将三种土壤从上至下装填至一维柱，1-2层、3-4层、5-6层分别为土壤A、B、C。随着入渗溶液pH的减小或NaCl溶液浓度的增加，铵态氮能够迁移至更深层的土壤；而硝酸盐氮迁移受溶液pH值及NaCl溶液浓度影响较小。当改变土壤装填顺序时（土壤ABC由上至下装填命名为土柱A-B-C，土壤粒径由小至大，反之命名为土柱C-B-A），土柱A-B-C中铵态氮浓度随着深度的增加逐渐减小，浓度最大值处于土柱的第1层，之后铵态氮浓度依次递减；对于土柱C-B-A，铵态氮浓度随着土壤深度增加呈现先增大后减小的趋势，浓度最大值处于第3层，在相同的入渗条件下，铵态氮及硝酸盐氮在粒径由粗至细的土壤中迁移深度要高于在粒径由细至粗的土壤中的迁移深度。

    （4）通过土柱试验对比入渗灌溉用水（土柱1）和生活污水（土柱2）对地下水硝酸盐氮浓度升高的影响，相同入渗条件下，土柱1中0～40 cm土壤溶液铵态氮的含量要小于土柱2中铵态氮的含量。高浓度铵态氮绝大部分集中在土柱的0～20 cm处，但随着入渗次数的增加，溶液中铵态氮依然能迁移至深层土壤。经过长时间多次入渗后，土柱2整体硝酸盐氮含量要高于土柱1。土柱2所产生硝酸盐氮的浓度值约为土柱1硝酸盐氮浓度值的8倍（模拟入渗溶液中不含硝酸盐氮）。土柱1和2第二次采样时土壤含水量及土壤溶液pH值整体波动较大，其值小于第一次采样值，结合出水端硝酸盐浓度值可以发现土柱1和2内部均发生了硝化反应，土柱2中硝化反应更剧烈；土壤DO值呈现略微下降的趋势，但整体浓度高于5 mg/L，所以土柱中的硝酸盐氮基本不发生反硝化作用。

  Groundwater nitrate pollution is an urgent problem in the world. In this study, we selected the characteristic agricultural vegetable planting areas in the Dagu River Basin in Qingdao, China. In order to explore the effects of agricultural irrigation and domestic sewage discharge on the increase of nitrate and nitrogen concentration in groundwater under the same infiltration conditions. three representative soils in the study area (named soil A, soil B, soil C, respectively) were selected. Through batch experiments, one-dimensional soil column simulation experiments and model migration verification simulation, the basic physical and chemical properties of the soil in the study area, the hydrodynamic conditions of the aerated zone soil and the nitrogen background value were determined. And the effects of soil environmental conditions on nitrogen conversion were explored. Taking ammonium nitrogen and nitrate nitrogen as the main research objects, the effects of soil solution pH, soil salinity, soil water content, initial nitrogen source concentration, and soil layering on the migration and transformation of the two were investigated. It could provide some scientific basis for the treatment of nitrate pollution in groundwater. The main conclusions were as follows:

  (1) Through batch experiments of nitrogen conversion, the results have shown that nitrification of ammonium nitrogen in soil occured only under aerobic conditions. Increased oxygen content or substrate concentration in the soil could promote the occurrence of nitrification reactions; When the soil moisture was less than 10%, it would have a lagging effect on nitrogen conversion and reduced the conversion of nitrogen; When the soil moisture was higher than 10%, the time of nitrification would be delayed, but it would not reduce the rate of ammonium nitrogen conversion. The ammonium nitrogen in the soil would not all participate in the nitrification reaction, and the ammonium nitrogen participating in the reaction was all converted into nitrate nitrogen. When glucose was used as the carbon source for nitrate nitrogen denitrification, the denitrification in the soil was proportional to the soil carbon-nitrogen ratio.

  (2) The process of determining the adsorption of ammonium nitrogen and nitrate nitrogen in soils A, B, and C by batch experiments found that the logarithmic and quasi-second-order kinetic equations could be better fitted the kinetic adsorption process of ammonium nitrogen and nitrate nitrogen respectively; The adsorption isotherms were in accordance with Freundlich and Langmuir adsorption models, respectively. As the pH or NaCl concentration of the soil solution decreased, the soil’s adsorption of ammonium nitrogen gradually increased. The amount of nitrate nitrogen adsorbed by the soil showed a tendency to decrease first and then increased with the increase of the pH value of the solution. It was less affected by NaCl concentration. The overall retardation coefficient of layered soils had a linear sum relationship with the thickness ratio of each layered soil and the retardation coefficient of single soil; When the difference in bulk density of layered soil was small, the relationship between the layered soil equivalent distribution coefficient and the single soil layer distribution coefficient could be well described by the linear superposition relationship of the layered distribution coefficient and thickness.

  (3) Soil A, B, and C were filled into a one-dimensional column from top to bottom, and Layers 1-2, 3-4, and 5-6 were soils A, B, and C, respectively. With the decrease of the pH value of the infiltration solution or the increase of the NaCl solution concentration, the ammonium nitrogen could migrate to deeper soil; The migration of nitrate nitrogen was less affected by the pH of the solution and the concentration of the NaCl solution. When the soil filling sequence was changed (the soil A，B，C from top to bottom is named soil column A-B-C, the soil particle size was from small to large, otherwise it was named soil column C-B-A). The concentration of ammonium nitrogen in soil column A-B-C gradually decreased with the increase of depth, the maximum concentration was at the 1st layer of the soil column, and then the ammonium nitrogen concentration decreased sequentially; For soil column C-B-A, the concentration of ammonium nitrogen showed a trend of increasing first and then decreasing with the increase of soil depth. and the maximum concentration was at the third layer. Under the same infiltration conditions, the depth of migration of ammonium nitrogen in soil with coarse to fine particle diameter was higher than that in soil with fine to coarse particle diameter;

  (4) The effects of infiltration irrigation water (soil column 1) and domestic sewage (soil column 2) on the increase of groundwater nitrate nitrogen concentration were compared through soil column test. Under the same infiltration conditions, the content of ammonium nitrogen in the soil solution of 0~40 cm in soil column 1 was less than that in soil column 2. The high concentration of ammonium nitrogen was mostly concentrated in the soil column at 0~20 cm, and with the increase of the number of infiltrations, the ammonium nitrogen in the solution could migrate to the deep soil. After a long period of multiple infiltration, the overall nitrate nitrogen content of soil column 2 was higher than that of soil column 1. Tthe concentration value of nitrate nitrogen produced by soil column 2 was about 8 times that of soil column 1(There was no nitrate nitrogen in simulated infiltration soluion). During the second sampling of soil columns 1 and 2, the soil moisture and the pH value of the soil solution fluctuated, which was less than the value of the first sampling. Combined with the nitrate concentration value at the outlet end, it could be found that nitrification reactions have occurred in both soil columns 1 and 2, and the nitrification reaction in soil column 2 was more intense; The DO of the soil value showed a slight downward trend, but the overall concentration was higher than 5 mg/L, so the nitrate nitrogen in the soil column basically did not undergo denitrification.