岩溶水系统对大气CO_2的潜在影响——基于热力学的研究

Geochemistry of Water System in Karst Regions and the Atmospheric CO_2 :Thermodynamic Studies

认识不同条件下岩溶水释放或吸收CO2的反应过程是研究碳酸盐岩对碳循环响应的前提和基础。本文从吉布斯自由能的热力学原理出发,对全球不同岩溶地区162组岩溶水(河水、溪水、湖水等)进行了热力学研究,结果显示:1)河水、溪水、湖水和洞穴滴水等岩溶水所处的环境因方解石矿物沉积而释放CO2成为大气CO2一个潜在的源;2)地下水在所处的环境下由于方解石的溶解而吸收CO2,成为大气CO2一个潜在的汇;3)少数出露点的泉水所处的环境既可发生方解石的溶解而吸收CO2,成为大气CO2的潜在汇,也可发生方解石的沉积而释放CO2,成为大气CO2的潜在源;4)在洪水期,泉水的水化学特征变化并未导致对大气CO2潜在贡献在源汇之间的跨跃性转变。162组岩溶水数据中,所有河水与溪水皆无一例外地在释放CO2。结果表明,从吉布斯自由能的热力学原理出发,研究岩溶水系统对大气CO2潜在源汇的贡献,没有条件约束,是一种较好的途径。

It is believed that to study the CO2 releasing or absorbing processes of the Karst water corresponding to the dissolution or formation of carbonate in various environments is the precondition and base for studying carbon cycling effect caused by the dissolution or formation of carbonate. By using Gibbs free energy thermodynamic theory, 162 batches of data for waters sampled from rivers, streams, lakes, springs, underground rivers etc. in different Karst regions were collected for thermodynamic study. Our results have revealed that, 1） The waters in rivers, streams, lakes, and dripping waters in caves could release COs to atmosphere due to the deposition of calcite. They could be potential sources for CO2 in atmosphere; 2） The underground waters could absorb CO2 due to the dissolution of carbonate. They could be sinks of COs indirectly, 3） The spring waters could not only absorb CO2 due to carbonate dissolution but also release CO2 due to carbonate deposition. They could be sinks or sources of CO2 indirectly; 4） the variation of hydrochemical characters of spring waters in flooding period does not change their original properties as sinks or sources of CO2 dramatically. It is indicated that all river waters and spring waters are relea- sing CO2 into atmosphere, based on 162 batches of data. The results show that the Gibbs free energy thermodynamic theory could be used to study if the water in Karst areas could be the potential sources or sinks of CO2 in atmosphere without any limitation.