重庆市青木关地下河水化学及其δ13C DIC变化特征

为了确定地下水中溶解无机碳和地下水中物质的来源,于2010年4月至2011年1月对重庆市青木关地下河流域系统进行了连续监测,分析其常规水化学组成、溶解无机碳含量及其同位素(δ13CDIC)组成变化特征及影响因素,2010年农耕期间(5-6月)又对部分观测点进行了加密取样分析.分析结果表明:(1)地下河水为HCO3-Ca型,其变化受水岩作用和降水作用的影响；(2)地下水中(Ca2++ Mg2+)/HCO3-的摩尔比值为0.6～0.72,平均为0.67,表明碳酸盐岩溶解受C3植被下土壤CO2、HNO3和H2SO4的共同作用的影响；(3)地下河水中由碳酸溶解碳酸盐岩产生的HCO3-]的贡献率为56.16％～81.25％,平均为66.96％,硝酸和硫酸溶解碳酸盐岩产生的HCO3-]的贡献率为18.75 ％～43.84％,平均为33.04％；(4)青木关地下河出口地下水的δ13 CDIC变化范围为-8.17‰～-13.68‰,平均值为-10.53 ‰.农耕期和枯水期地下河水的δ13 CDIC平均值分别为-9.25‰ 和-12.29‰,农耕期较枯水期偏正,偏正幅度达3‰,表明人类农业活动物质输入对地下河水δ13 CDIC有较大的影响.

Hydrochemistry and variation of δ^13CDIC of the Qingmuguan underground river in Chongqing

In order to determine the source of dissolved inorganic carbon and the matter in the Qingmuguan underground river system, the underground river system is monitored from April, 2010 to January, 2011, and the chemical components, the dissolved inorganic carbon content and δ^13CDIC as well as their influencing factors are analyzed. Furthermore, detailed analysis is made to some monitor points in the ploughing season in 2010. The results show that （1） the type of the Qingmuguan underground river water is Ca-HCO3 that is affected mainly by water-rock action and rainfall; （2） the molar ratio of （Ca^2＋ ＋Mg^2＋ ）/HCO3^- in the groundwater varies from 0.6 to 0.72 and is averaged 0.67 , which indicating the carbonate dissolution is con- trolled by CO2, HNO3 and H2SO4 in the soil under the C3 vegetation cover; （3） the HCO3^- from carbonate dissolution by carbonic acid account for 56.16% to 81.25 % of the total HCO3^- concentration in groundwater with a mean percentage of 66.96%, while the HCO3^- from carbonate dissolution by sulphuric and nitric acids make up 18.75 % to 43.84% of the total HCO3^- concentration in groundwater with a mean percentage of 33.04 %; （4） the ~13 CDIC in groundwater varies from - 8. 17 % to -- 13. 68 % with an average value of -10.53 No, the average value of δ^13CDIC in ploughing and dry season is -9.25 N0 and -12.29 %o respective- ly, which indicates there is a significant perturbation to the cycling and export of inorganic carbon by agricultural activities in karst underground river system.