奈曼旗农牧交错带地处科尔沁沙地腹地生态脆弱区，其地下水水化学形成机制与背景值 研究可支撑水资源配置及农牧业绿色发展。基于水文地质调查与水文地球化学分析，结合自组织 映射神经网络与K-means 聚类混合算法，揭示了地下水化学组成、主控过程及环境背景值。结果表 明：地下水化学组成空间差异性强，但水化学类型均以HCO3-Ca·Mg 为主，呈弱碱性；地下水化学演 化主要受碳酸盐矿物的溶解—沉淀以及硅酸盐矿物的风化溶解驱动，同时受控于正向阳离子交替 吸附作用；总铁、F-、TDS 和NO3-N是影响奈曼旗地下水质量的关键指标，通过水文地球化学图解 法、Grubbs 检验及自组织映射神经网络多方法联合估算其视背景值范围分别为0.42~0.56 mg/L、 0.34~0.38 mg/L、181~188 mg/L 和0.22~1.58 mg/L，其中，总铁的高背景可能与菱铁矿溶解有关，而 F-富集则受控于萤石溶解及正向阳离子交替吸附作用。这为区域水资源优化管理、污染防治及生 态保护提供了科学依据。

Abstract：The farming-pastoral zone in Naiman Banner is located in the hinterland of of Horqin Sandy Land. The research on the formation mechanism and background value of groundwater hydrochemistry supports the allocation of water resources and the green development of agriculture and animal husbandry. Based on hydrogeological survey and hydrogeochemical analysis, combined with self-organizing map neural network (SOM) and K-means clustering hybrid algorithm, this study revealed the characteristics of groundwater chemical composition, main controlling factors and environmental background values. Results indicated significant spatial heterogeneity in groundwater chemistry, with HCO3-Ca·Mg as the predominant hydrochemical type and weakly alkaline characteristics. Groundwater chemical evolution is primarily driven by dissolution-precipitation of carbonate minerals and weathering of silicate minerals, and controlled by alternating positive cation adsorption. The apparent background values of Total Fe (TFe), F- , TDS and NO3-N, key indicators affecting the quality of groundwater in Naiman Banner, were 0.42~0.56 mg/L, 0.34~0.38 mg/L, 181~188 mg/L and 0.22~1.58 mg/L, respectively, which were estimated by using a coupled approach of hydrogeochemical graphic method, Grubbs test and SOM. The high background of TFe may be related to siderite dissolution, while the F- enrichment is controlled by fluorite dissolution and alternating positive cation adsorption. This research elucidates the groundwater background values and hydrochemical formation mechanisms in the farming-pastoral zone of Naiman Banner, providing scientific support for the optimization management of regional water resource, pollution prevention, and ecological conservation.