利用水化学方法识别岩溶水文系统中的径流

Identifification of Runoff in Karst Drainage System Using Hydrochemical Method

通过暴雨中的野外观测,确认了桂林丫吉试验场S31泉岩溶水文系统中多种径流形式:表层岩溶带管道流、回归流、坡面流和壤中流。现场测量发现不同形式径流的水化学特征(pH、电导率、Ca2+、HCO3-)存在差异,Ca2+的质量浓度相差最大可以达到3倍。从CaCO3-H2O-CO2平衡体系来看,CO2分压(pCO2)对径流的水化学特征具有控制作用。在大气pCO2影响下的岩溶水矿化度较低,而土壤空气pCO2达到2.7%,是大气的近百倍,其影响的径流矿化度较高。鉴于大气中和土壤中pCO2的显著差异,从水化学特征上将径流分为2类,并且认为它们构成了系统出口洪水的2个主要来源。在此基础上利用水化学方法计算出S31岩溶泉洪水时的径流构成。结果表明,在暴雨的情形,由大气pCO2环境产生形成的岩溶水的比例占到泉水总量的70%,进一步证明了快速流在岩溶水中的重要作用。

Some kinds of runoff were identified in a karst hydrological system by observation and monitoring in field during rain storm events at YAJI hydro-geological site,Guilin,China.Runoff includes many forms such as epikarst springs,slope return flow,overland flow and soil interflow in a depression.The runoff aroused by rainfall has different residence time and hydrochemistry.A multi sensor for pH and specific electrical conductivity together with calcium and bicarbonate concentration were used to determine the chemical composition of stream water,spring,drop water and stored water in rock holes.The results are quite different among these kinds of karst water,indicating that the chemical items of water can be used for tracing the sources of spring.Calcite dissolution in pure water with different pCO2 was calculated by PHREEQC.We get a line of Ca2＋ concentrations at different pCO2.The dots representing different water in the system were near the theoretical line of Ca2＋ concentration VS pCO2 in CaCO3-H2O-CO2（g） system.It showed that the chemical character of runoff was controlled by pCO2.Runoff was classified into two groups according to its hydrochemistry based on difference of pCO2 in atmosphere and soil.The two groups were end numbers of spring water in flood.It showed that event water controlled by atmosphere but not soil air occupied about 70% when storm by end-number method.