塔城盆地地下水氟分布特征及富集机理

Distribution characteristics and enrichment mechanism of fluoride in the shallow aquifer of the Tacheng Basin

塔城盆地位于新疆维吾尔自治区西北部,干旱少雨,蒸发强烈。但相对于新疆其他盆地,塔城盆地地下水水质相对较好,溶解性总固体和F-含量相对较低。为解译这种差异及盆地内高氟地下水的成因,本文在对盆地地下水样品水化学组分系统分析的基础上,结合多种水文地质调查数据,利用数理统计、离子比及主成分分析等手段,研究高氟水的成因及其分布规律。结果表明:受气候以及地质等因素控制,研究区地下水氟浓度总体较低,高氟水主要分布于扇前洼地及盆地中部的低洼地带;受承压含水层的顶托补给,地下水氟浓度呈现出上高下低的垂向分带特征。研究区地下水径流途径短,水循环快,水岩相互作用时间较短,且山区地下水以深径流形式循环补给平原区深层承压含水层,再顶托补给潜水,避免了强烈的蒸发浓缩作用。山前洪积扇地下水氟富集主要受控于沉积地层中含氟矿物的风化溶解,而岩石风化、蒸发浓缩、阳离子交换、竞争吸附为平原区地下水氟浓度的主要影响因素。

The Tacheng Basin is located in the northwestern Xinjiang Hui Autonomous Region(XHAR),which is characterized by drought,less rain and strong evaporation.Compared with other basins in XAR,the concentrations of total dissolved solids(TDS) and fluoride(F-) in the groundwater in the Tacheng Basin were relatively low.To explain this different distribution characteristics and enrichment mechanism of F in the groundwater,statistical analysis,including principal component analysis,was used based on the hydrochemical data of groundwater samples in this region.The results showed that the concentration of F-in groundwater was generally low due to the climatic and geological factors in the region.The high-F-groundwater was mainly distributed in the marsh lands of the front and central regions of the basin.The concentration of F was high in shallow and low in deep unconfined aquifers,controlled by an upward recharge from deep confined aquifer.The groundwater runoff was relatively short and the groundwater circulation was fast in this region,causing a short interaction time between groundwater and rock.In addition,the deep confined aquifer of the plain was recharged from the groundwater in the mountainous area by an upward hydraulic gradient flow,which further replenished the upper shallow unconfined aquifer.Thus,the evaporation and concentration process was very weak in this recharge mode.The concentration of F in the groundwater was mainly controlled by the weathering and dissolution of fluoride-bearing minerals in the sedimentary strata in the piedmont alluvial-pluvial fan,with rock weathering,concentration by evaporation,cation exchange,and competitive adsorption as the main influencing factors.