铁锰超标地下水在我国分布广泛，这类含铁含锰地下水储量占据我国地下水总储量的20 %以上，铁锰超标对水质安全有着重要影响。而寻求地下水铁锰超标问题治理办法的关键是研究地下水体中铁锰来源。基于此，本文以西安市西郊沣皂河、北郊泾渭河和东郊灞河傍河水源地为研究区，开展沿河地下含水层铁锰赋存特征、铁锰释放规律及不同酸碱度降水/灌溉水入渗补给条件下的铁锰迁移转化规律研究。研究将丰富降水/灌溉水—地下水系统中环境地球化学行为研究理论、对地下水资源合理开发利用以及地下水水质安全管理具有重要的理论意义与实践指导价值。取得了以下主要成果：

（1）依据《地下水质量标准》（GB/T 14848-2017）列举的浑浊度、pH、氨氮、总溶解性固体、总硬度、铁和锰等39项指标，对研究区127组地下水水样进行分析和水质评价。其中，沣河沿岸地下水水质最好，均属于Ⅲ级水或优于Ⅲ级水，泾渭河沿岸地下水水质较差。探明研究区水质超标的主控因子为铁、锰、氨氮。

（2）采用钻孔取芯方法结合室内实验，获取原状岩土样中铁锰的赋存形态。岩芯各形态铁锰含量以残渣晶格结合态铁锰最高，水可溶态铁锰最低。有效性铁锰分别介于全铁、全锰含量的27.16 %~38.79 %和27.72 %~42.42 %之间，非有效性铁锰分别介于全铁、全锰含量的61.21 %~72.84 %和57.58 %~72.28 %之间。在三个研究区不同粒径岩土样中，圆砾石的铁锰含量均最低，粉质粘土、细砂、中粗砂的铁锰含量差异较大。

（3）利用室内静态释放实验，研究地层岩性对铁锰的静态释放规律。铁锰的释放速率具有一致性，均为前期快速释放，直至达到饱和状态后释放速率开始下降，最终倾向于一种动态稳定状态。铁达到最大释放量需要10天，锰达到最大释放量需7天，在达到最大释放量之后上覆水体铁含量迅速降低至0.140 mg/L以下，而锰含量呈现缓慢下降的趋势降至0.122 mg/L以下，并最终和铁共同在第28天趋于稳定。

（4）通过土柱淋溶模拟实验，探讨降水入渗路径地下水系统岩土体中铁锰的迁移规律及转化机制。土柱淋溶实验表明，渗出水的铁锰含量均随时间变化大致呈现“升高—平衡—降低”的分布趋势，渗出水中锰含量最高值0.181 mg/L于第7天出现在酸性柱的第2出水口，释放率为0.071 %；铁含量最高值0.458 mg/L于第21天出现在酸性柱的第4出水口，释放率为0.036 ‰，可见锰的迁移转化速率较铁更快，释放率也更大。

（5）根据前述研究成果建立不同酸碱度入渗水在地下水中运移的耦合动力数学模型，对不同酸碱度入渗水在地下水中迁移的动态过程进行了模拟，分别预测了近期（1年）、中期（5年）、长期（10年）地下含水层铁锰分布特征。结果表明：酸性、中性、碱性条件下，入渗水短期内都会使地下水系统岩土体中的铁锰开始释放；铁锰污染物沿着入渗点在纵向贯穿；中期和长期来看，污染团出现明显的横向扩散。铁锰的释放规律呈现高度一致。

Groundwater with excessive iron and manganese is widely distributed in China and occupies more than 20 % of the total groundwater reverses. Excessive iron and manganese have an important impact on the groundwater quality. The key to solve the problem of excessive iron and manganese in groundwater is to find out the source of iron and manganese. Based on this, this study took the water source of Fenghe River and Zaohe River in the western suburb, Jinghe River and Weihe River in the northern suburb and Bahe River in the eastern suburb of Xi'an as the study areas, and studied the occurrence characteristics, release law of iron and manganese in groundwater aquifers along the river and investigated the migration and transformation mechanism during precipitation/irrigation water infiltration with different pH. Therefore, this paper has important theoretical significance and practical guiding value for enriching the research theory of environmental geochemical behavior in precipitation and irrigation water-groundwater system, rational development and utilization of groundwater resources and safety management of groundwater quality. The following main results have been achieved:

(1) According to 39 indexes listed in Groundwater Quality Standard (GB/T 14848-2017), such as turbidity, pH, ammonia, total dissolved solids, total hardness, iron and manganese, this study analyzed the water samples and evaluated the water quality of the 127 groundwater samples collected in the study areas. The result is: the groundwater quality along Fenghe River is the best, which belongs to Type III water or better than that, while the groundwater quality along Jinghe River and Weihe River is relatively poor. It is proved that the main control factors of water quality exceeding the standard in the study areas are iron, manganese and ammonia.

(2) Through drilling and laboratory experiments, the occurrence forms of iron and manganese in undisturbed rock-soil samples were obtained. Residue (Fe/Mn) ranks the highest in the content of all forms of iron and manganese in the core, while water soluble (Fe/Mn) ranks the lowest. Available iron and manganese are between 27.16 % ~ 38.79 % and 27.72 % ~ 42.42 % of total iron and total manganese, respectively, and unavailable iron and manganese are between 61.21 % ~ 72.84 % and 57.58 % ~ 72.28 % of total iron and total manganese, respectively. Among the lithologic rock-soil samples with different grain sizes collected from 3 study areas, the iron and manganese content of round gravel is the lowest, while the iron and manganese content in silty clay, fine sand and medium coarse sand is quite different.

(3) With the help of indoor static release experiment, the static release of iron and manganese by stratum lithology was studied. The release rates of iron and manganese are consistent, both of which are rapid in the early stage, and then begin to decline after reaching saturation state, and finally tend to maintain a dynamic stable state. It takes 10 days for iron to reach the maximum release amount, and 7 days for manganese to reach its maximum release amount. After reaching the maximum release amount, iron content in overlying water decreases rapidly below 0.140 mg/L, while manganese content decreases slowly below 0.122 mg/L, and finally stabilizes together with iron on the 28th day.

(4) Through leaching simulation experiment, the migration and transformation mechanism of iron and manganese in groundwater system rock-soil along precipitation infiltration path were discussed. The rock-soil column leaching experiment shows that the iron and manganese content of exudate water has a distribution trend of "increase-balance-decrease" with time, the highest manganese content of 0.181 mg/L appears at the second outlet of acid column on the 7th day, with a release amount of 0.071 %, and the highest iron content of 0.458 mg/L appears at the fourth outlet of acid column on the 21st day, with a release amount of 0.036 ‰. It can be seen that the migration and transformation rate of manganese is faster than that of iron, and the release amount of manganese is larger than that of iron as well.

(5) According to the previous results, a coupled dynamic mathematical model of infiltration water with different pH in groundwater was established, and the dynamic process of infiltration water with different pH in groundwater was simulated, and the distribution characteristics of iron and manganese in underground aquifer in recent (1 year), medium (5 years) and long term(10 years) were predicted respectively. The simulation results shows that under acidic, neutral and alkaline conditions, the infiltration water will start to release iron and manganese in the rock-soil of groundwater system in a short time; Iron and manganese pollutants will penetrate longitudinally along the infiltration point; In the medium and long term, the pollution mass will have obvious horizontal diffusion. The release of iron and manganese are highly consistent.