河套灌区地下水化学时空特征及环境驱动因素

Chemical Spatiotemporal Characteristics and Environmental Driving Factors of Groundwater in Hetao Irrigation Area

为探明内蒙古河套灌区地下水水化学特征及其环境成因,以内蒙古河套灌区乌兰布和、解放闸、永济、义长和乌拉特这5个灌域为研究区,选取72眼地下水观测井,于冻融末期(3月)、灌溉中期(7月)和秋浇末期(11月)这3个典型时间段采集地下水216个水样.综合运用统计分析、Piper三线图、Gibbs图、离子比值和主成分分析等方法研究和探讨了地下水化学环境变化规律和地下水组分形成的环境驱动因素.利用水质指数(WQI)法评价了地下水的饮用适宜性,采用USSL图与Wilcox图综合分析地下水的灌溉适宜性.结果表明,研究区地下水普遍咸化,地下水阴、阳离子总浓度排序均为:冻融末期<秋浇末期<灌溉中期,Na+和Cl-是水化学的主要贡献离子.地下水水化学类型以Cl-Na型占主导,Cl·SO_(4)-Ca·Mg型次之,SO_(4)-Ca·Mg、HCO_(3)·Cl-Na、HCO_(3)-Na和HCO_(3)-Ca·Mg型多种共存.河套灌区浅层地下水基于WQI值分类,主要为Ⅳ类和Ⅴ类,总体地下水水质较差.USSL图与Wilcox图图解综合评价结果表明,灌区浅层地下水中盐度、钠浓度普遍偏高,冻融末期、灌溉中期和秋浇末期分别有80.6%、76.1%和77.6%的水样不适宜灌溉.研究区地下水化学特征的主要控制因素为蒸发浓缩作用和岩石风化作用,其中Na^(+)和Cl^(-)主要来自盐岩的溶解和阳离子交换作用,农业灌溉和干旱是河套灌区地下水水化学演化的主要驱动因素.研究成果可为内蒙古引黄灌溉区优化农业管理措施提供技术支持,并为合理利用地下水资源提供理论参考.

To explore the chemical characteristics and environmental factors of groundwater in the Hetao Irrigation Area of Inner Mongolia,five irrigation fields,including UulanBuh,Jiefangzha,Yongji,Yichang,and Wulat,were selected as the research area.From 72 groundwater observation wells,a total of 216 groundwater samples were collected throughout three typical periods:the end of freeze-thaw(March),the middle of irrigation(July),and the end of autumn watering(November).Comprehensive methods were utilized,such as statistical analysis,Piper three-line diagram,Gibbs diagram,ion ratio,and principal component analysis,to explore the changes in the groundwater chemical environment and the environmental driving factors of groundwater component formation.The groundwater drinking suitability was evaluated using the water quality index(WQI),and the irrigation suitability was analyzed using the USSL and Wilcox plots.The results indicated that the groundwater in the research areas was generally saline,and the total anion and cation concentrations in each period in ascending order were as follows:late freeze-thaw stage,late autumn irrigation stage,and mid-irrigation stage,with Na^(+)and Cl^(-)being the major contributing ions.The chemical type of groundwater was dominated by Cl-Na,followed by Cl·SO4-Ca·Mg and a coexistence with SO_(4)-Ca·Mg,HCO_(3)·Cl-Na,HCO_(3)-Na,and HCO_(3)-Ca·Mg.Based on WQI values,the shallow groundwater in Hetao Irrigation District was mainly classified as Class IV and Class V,and the quality was poor in general.According to the USSL diagram and Wilcox diagram,the comprehensive evaluation results showed that the salinity and sodium concentration of shallow groundwater in the irrigation area were generally high.A total of 80.6% of the water samples during the late freeze-thaw period,76.1% during the mid-irrigation period,and 77.6% during the late autumn irrigation period lacked irrigation suitability.Two major controlling factors of groundwater chemical characteristics were present in the study area,namely,evaporation and rock weathering,and Na^(+)and Cl^(-)mainly came from the dissolution and cation exchange of salt rocks.Agricultural irrigation and drought were the chief driving factors of groundwater chemical evolution in the Hetao Irrigation Area.The study provides technical support for optimizing agricultural management measures and a theoretical reference for rational utilization of groundwater resources in the Yellow River irrigation area of Inner Mongolia.