长江中上游结合带喀斯特小流域夏季水化学特征——以宜昌下牢溪为例

Hydrochemical Characteristics of Small Karst Watershed in the Junction Zone of the Middle and Upper Yangtze River in Summer:a Case Study of Xialaoxi River in Yichang

河流的水化学组成受自然因素和人为因素的综合影响,研究河流水化学特征有助于了解流域内物质循环及人类活动的干扰情况.针对长江中上游结合带喀斯特小河流下牢溪,于2019年6月至8月间进行了八大离子及相关环境因子的采样及监测.结果表明:下牢溪水化学类型为HCO_3~--Ca~(2+)-Mg~(2+)型,HCO_3~-占阴离子总当量浓度的85.59%,Ca~(2+)、Mg~(2+)分别占阳离子总当量浓度的48.96%和48.79%.相较于长江流域内其他喀斯特河流,下牢溪具有更高的HCO_3~-和Mg~(2+)浓度水平.河流水化学组成主要受到岩石风化控制,Ca~(2+)、Mg~(2+)、HCO_3~-主要来源于白云岩、石灰岩的溶解,Na~+、K~+、Cl~-、SO_4~(2-)、NO_3~-主要来自于生活污水和农业面源的输入.下牢溪Ca~(2+)、Mg~(2+)、HCO_3~-浓度自上游向下游逐渐降低,而Na~+、K~+、Cl~-和SO_4~(2-)浓度呈现往下游方向递增的趋势,下牢溪中下游受人为活动影响更为明显.

The chemical composition of rivers is comprehensively affected by natural factors and human factors.Investigating hydrochemical characteristics of river is beneficial to understand the circulation of substances and the disturbances of human activities to the watershed.Focusing on the Xialaoxi River,a typical karst river in the junction zone of middle and upper reaches of the Yangtze River,the eight major ions and related environmental factors were sampled and monitored from June to August in 2019.The results show that,the hydrochemical type of Xialaoxi River is HCO3--Ca2+-Mg2+.HCO3-accounts for 85.59%of the total equivalent concentration of anions,and Ca2+and Mg2+account for 48.96%and 48.79%of the total equivalent concentration of the cations respectively.Xialaoxi River exhibits higher concentrations of HCO3-and Mg2+comparing to other karst rivers within the Yangtze River Basin.Hydrochemical composition of the river is mainly controlled by rock weathering.Ca2+,Mg2+and HCO3-mainly originated from the dissolution of dolomite and limestone,while Na+,K+,Cl-,SO42-and NO3-are mainly from domestic sewage and agricultural non-point sources.The concentrations of Ca2+,Mg2+and HCO3-in Xialaoxi River gradually decreases from upstream to downstream,while the concentrations of Na+,K+,Cl-,SO42-shows an increasing trend toward the downstream direction.The middle and lower reaches of Xialaoxi River are more affected by human activities.