甘肃省秦王川盆地地下水氟富集特征及影响因素

Evolution feature and gensis of fluoride groundwater in shallow aquifer from Qin Wangchuan basin

随着"一带一路"工作的推进,秦王川盆地作为兰州市新城区,地下水需水量持续增大,水资源短缺问题已成为研究区发展的主要制约因素。但盆地地下水氟分布特征及成因不明,这使得未来的地下水开发利用存在较大风险。因此,文中在对盆地内地下水进行系统采样分析的基础上,利用数理统计、离子比及主成分分析等方法研究了秦王川盆地地下水氟分布特征及成因。结果表明,研究区地下水氟含量总体偏高,大面积分布0.5~1.0mg/L的中氟水,盆地西北部山前及平原区中部出现高氟水。高氟水以HC3·SO4-Na、Cl·SO4-Na型水为主,表现出富钠、贫钙,弱碱性特点。地层中的含氟矿物萤石的溶解是盆地地下水中氟离子的主要来源,而方解石、白云石等含钙矿物抑制氟离子的溶解与富集。地下水氟富集受控于岩石风化溶解及蒸发浓缩作用,同时受阳离子交换、解吸与竞争吸附等作用影响。受"引大入秦"工程农业灌溉回归淡水淋洗补给,地下水氟离子含量未随溶解性总固体的升高而明显升高。

With the promotion of the"one belt and one way"work,the groundwater demand for the Qinwangchuan basin,as a new urban area of Lanzhou,has continuously increased.However,the distribution characteristics and causes of fluoride of groundwater in the basin are unknown,which makes the development and utilization of groundwater in the future risky.Based on the hydrochemical data,the distribution of groundwater with high fluorine content was analyzed by correlation analysis and principal component analysis combined with geological and hydrogeological conditions.Mineral dissolution and precipiration,evaporation,competitive adsorption and desorption,and cation exchange were integrated to discuss the major mechanisms controlling the enrichment of groundwater fluoride in the plain and the piedmont areas in Qin Wangchuan Basin with different hydrogeological conditions.The results show that the groundwater fluorine concentration is generally high,with a large area of 0.5-1.0 mg/L of medium fluorine water,and high fluorine water appears in the Piedmont and plain areas in the northwest of the basin.High fluorine water is mainly HCO3·SO4-Na、Cl·SO4-Na,which is rich in sodium,poor in calcium and weak in alkalinity.The dissolution of fluorine-bearing minerals in strata is the main source of fluoride ions in groundwater of the basin.Calcium-bearing minerals such as calcite and dolomite inhibit the dissolution and enrichment of fluoride ions.Fluorine enrichment of groundwater is controlled by rock weathering,dissolution,evaporation and concentration,as well as cation exchange,desorption and competitive adsorption.The fluoride ion content of groundwater does not increase significantly with the increase of total soluble solids due to the return of agricultural irrigation to freshwater leaching and recharge.