酸雨溶蚀碳酸盐岩的源汇效应分析——以广西典型岩溶区为例

摘要

It is well acknowledged that the reaction between strong acids and carbonate rocks can release CO2,and then reduce the karst carbon sink.Acid rain is one of the sources of these strong acids.Carbonate rocks are widely distributed in Guangxi Zhuang Autonomous Region.Meanwhile,acid rain pollution is also common there,so that the reaction between acid rain and carbonate rocks is pervasive in this area.Seven acid rain monitoring sites in Guilin,Liuzhou,Hechi,Baise,Yulin,Nanning and Qinzhou represent the whole situation of Guangxi,where temperature,rainfall,and the degree of acid rain were studied in this work.The method of the carbonate-rock-tablet test is used to assess the intensity of the karst process at all sites.Precipitation parameters at these sites are collected at the same time.Based on the dissolution quantity of test blocks and precipitation parameters such as rainfall,rainfall duration,pH value and conductivity in a whole year(2014.5-2015.5),the factors of carbonate dissolution and source-sink effect of acid rain were analyzed.The results show that the dissolution quantity of test blocks is in accordance with the accumulative rainfall time which represents the dissolution time duration of rainfall to the test blocks.For a single acid rain,dissolution of the carbonate rock can be divided into two stages,(1) dissolution by strong acid with CO2 releasing;(2) dissolution by carbonic acid due to CO2 absorbing.The reaction between carbonate rocks and strong acid which is related to acid rain is a fast reaction.The result shows that the dissolution quantity of test blocks dissolved by strong acid is quite low,that is also the reason for the low correlation between dissolution quantity and the degree of acid rain such as pH and the rate of acid rain.Calculation results show that carbonate rocks dissolved by carbonic acid is the main process at all the sites.About 0.27％ to 3.52％ with the average of 1.96％ of dissolution quantity should be deducted because of the acid rain in a whole year.It is lower than 10％ to 30％ which is calculated by river water chemistry.This is because of additional sources of the acid,such as weathering of sulfide deposits,and agricultural and industrial activities.The proportion carbonate rock dissolution is small in the study area,but it will increase exponentially while the pH value decreases as shown in computational formula.Therefore,the acid rain has a significant effect on karst carbon sink,which cannot be ignored.%选取广西的桂林、柳州、河池、百色、玉林、南宁、钦州7个酸雨监测点进行了为期一年(2014年5月至2015年5月)的监测,结合各站点溶蚀试片和降雨降雨量、降雨时间、pH值和电导率等,分析了试片溶蚀量的主要影响因素及酸雨的源汇效应.结果表明,试片溶蚀量与累计降雨时间,即溶蚀作用发生的时间关系密切.单场酸雨对碳酸盐岩的溶蚀过程可分为两个阶段,即:前期强酸溶蚀碳酸盐岩,释放CO2,为碳源;后期碳酸溶蚀碳酸盐岩,吸收大气CO2,为碳汇.而就整年雨言,碳汇过程占绝对优势,酸雨减汇量仅占总溶蚀量的0.27％～3.52％,平均为1.96％,但酸雨减汇比例随酸雨pH值的降低而呈指数增加.酸雨对岩溶碳汇有着显著影响,在岩溶碳汇的研究中不应忽视.