喀斯特洞穴滴水水文化学过程的时空变化及其环境指示——以贵州织金洞为例

Temporal and Spatial Variation of Water Chemistry and Environmental Indication of Drip Water in Karst Cave——A Case Study of Zhijin Cave,Guizhou Province

洞穴水地球化学过程的研究对于洞穴内次生沉积物景观的发育有着重要的意义,2015年1—12月通过现场滴定测量和实验室仪器分析对贵州织金洞洞穴水的水化学指标进行了为期一个完整水文年的动态监测,采样时间均为每月26—28日。结果表明:(1)洞穴滴水滴率和Ca^(2+),Mg^(2+),Sr^(2+)离子浓度均与降水量有很好的响应,但同时都表现出一定的滞后性,其中Mg^(2+),Sr^(2+)离子所携带的气候信号较为持久,Ca^(2+)离子浓度在雨季波动较大。(2)滴水水化学性质在化学计量上总体符合石灰岩喀斯特地区的侵蚀方程,Ca^(2+)/HCO_3^-的比值均在1/2上下波动;(3)滴水中的SIc和SId之间存在显著的正相关关系,滴水中的液相CO_2分压[lgPCO_2(water)]与pH值之间呈现出显著的负相关,体现了上覆土壤层中的高浓度CO_2对洞穴滴水化学过程的重要影响。(4)滴水中的Mg/Ca与Sr/Ca比值在雨季到来后的曲线变化呈现出明显的同增同减性特征,证明CaCO_3在未到达洞穴之前就已经在土壤层和基岩层中发生了优先沉积(PCP),致使运移到洞内的Ca^(2+)离子浓度相对其他离子的升高程度小;(5)滴水中Mg/Ca比值与Sr/Ca比值都有较明显的季节变化,但是Sr/Ca比值季节滞后性明显,而Mg/Ca比值年际变化更具波动性,对外界降水变化响应较敏感。

The study of the geochemical process of the cave is of great significance to the development of the secondary deposits in the cave.From January 2015 to December 2015,the water chemistry indexes of Zhijin Cave in Guizhou Province were monitored in a whole year.Results showed that：（1）the drip rate of dripwater and Ca2＋,Mg2＋,Sr2＋ ion concentrations had the very good response to precipitation,but also reflected the certain lag,and Mg2＋,Sr2＋ ions carried by the climate signal is very persistent,Ca2＋ ion concentration in the rainy season fluctuated;（2）drip water chemical properties in the chemical measurement were compliance with the erosion of limestone in Karst area on the overall,the ratio of Ca2＋/HCO3- was 1/2 with up and down fluctuations;（3）significant positive correlation between the drop of SIc and SId was founed,drop of water in the liquid phase partial pressure of CO2 [lgPCO2（water）]and pH values showed a significant negative correlation,reflecting the important influence of the high concentration of CO2 in the overlying soil layer of cave drip water chemical processes;（4）the Mg/Ca and Sr/Ca ratios of drip water in rainy season after the arrival of the curve show obvious increase and reduction of feature,indicating that CaCO3 has in the soil layers before it did not reach the cave,and the bedrock layer occurred prior calcite precipitation（PCP）,resulting in the increase of migrating to the inside of the Ca2＋ ion concentration was less compared with the other ions;（5）The ratios of Mg/Ca and Sr/Ca in drip water presented the obvious seasonal variation,but seasonal ratios of Sr/Ca lagged significantly,and Mg/Ca ratios of interannual variation was more volatility,the change response is sensitive to the outside precipitation.