沁河流域水化学组成的空间和时间变化特征

Spatial and temporal variations of hydrochemical compositions of river water in Qinhe Basin

选择我国北方小流域(沁河)作为研究对象,分丰水期(8月)和平水期(12月)采集干流和支流河水样品,结合野外现场测试和室内分析等方法,辨析河水化学组成的空间和时间变化特征,阐明人类活动和自然因素对河水溶解组分的控制作用。结果表明:(1)沁河流域河水丰水期和平水期阳离子主要以Ca^(2+)和Mg^(2+)为主,丰水期当量浓度占比均值分别为45%和41%,平水期分别为43%和41%。阴离子主要以HCO_3^-和SO_4^(2-)为主,丰水期当量浓度占比均值分别为46%和39%,平水期分别为55%和27%。水化学类型表现为HCO_3^--SO_4^(2-)-Ca^(2+)-Mg^(2+)。(2)丰水期河水δD和δ18O均值分别为-65.4‰和-8.76‰,平水期河水δD和δ^(18)O均值分别为-64.6‰和-8.68‰,大气降水是沁河河水主要补给来源,部分水体由于蒸发作用表现为富集氢氧同位素。(3)丰水期和平水期河水[SO_4^(2-)]/[HCO_3^-]当量浓度比值均值分别为0.96和0.54,[Ca^(2+)+Mg^(2+)]/[HCO_3^-]当量浓度比值均值分别为1.88和1.78,硫酸参与碳酸盐矿物化学风化过程,硫酸的来源包括酸雨和硫化物矿物氧化等。(4)沁河流域下游河水NO_3^-和THg含量逐渐升高,受人为活动影响较大,主要来源包括生活污水、工业废水以及农业活动等。

Qinhe Basin,a small watershed in North China,was chosen,and spatial and temporal variations of chemical composition in river water were described to illustrate the controlling roles of natural factors and anthropogenic activities on the base of two sampling campaigns during flood and normal seasons for mainstream and tributaries combined with onsite determination and indoor analysis. The results indicated that：（ 1） Cations were dominated by Ca^（2＋）and Mg^（2＋）in river water samples of Qinhe Basin during the two seasons accounting for 45% and 41% of total cations in terms of equivalent values during flood season and 43% and 41% during normal water season,respectively. Anions were dominated by HCO3^-and SO4^（2-）in river water samples and their ratios of equivalent values were 46% and 39% for flood season and 55% and 27% for normal season,respectively. The water type was mainly HCO3^--SO4^（2-）-Ca^（2＋）-Mg^（2＋）.（ 2） The average values of δD and δ^（18）O were-65.4‰ and-8.76‰ in flood season and-64.6‰ and-8.68‰ in normal season respectively. Atmospheric deposition was the main recharge sources for river waters in Qinhe and some of them with positive hydrogen and oxygen isotope values experienced evaporation.（ 3） The ratios of SO4^（2-）and HCO3^-in terms of equivalent values were 0.96 and 0.54 during flood and normal season respectively,and the ratios between Ca^（2＋）＋ Mg^（2＋）and HCO3^-equivalent values were1.88 and 1.78 in flood and normal season respectively. The sulfuric acid derived from acid rainand oxidation of sulfide minerals had participated in chemical weathering process of carbonate minerals.（ 4） Nitrate and total mercury concentrations of river waters gradually increased downstream,which indicated the influences from anthropogenic activities mainly including sewage water,industrial waste water and agricultural activities.