中文摘要：

稳定碳同位素是指示岩溶动力系统碳来源及转化的重要指标。为揭示重庆地区岩溶地下水中溶解无机碳基本特征和碳来源，本文对该地区63条岩溶地下河水样进行了水化学和碳同位素分析。研究结果表明，重庆地区地下河水溶解无机碳主要表现形式为HCO~-，雨季由于稀释作用其浓度低于旱季。重庆岩溶地下河水δ13C—DIC（V—PDB）旱季变化范围为一15．34‰～-5．89‰，雨季变化范围为-17．40‰～-4．23‰。根据δ13c同位素质量平衡方法，计算得到重庆地下河旱季碳酸盐岩溶蚀对DIC贡献为45．1％～79．7％，雨季平均为34．6％～82．1％。计算结果表明，在人类活动不断增强的情况下，岩溶水体DIC通量中碳酸盐岩溶解来源的DIC和其参与岩溶地下水δ13C值的形成并不一定是岩溶作用理论方程中所计算的50％，而是有一定的变化范围。因此在计算岩溶作用碳汇时，建议通过δ13C值扣除碳酸盐岩溶蚀形成DIC的通量后再来推算岩溶作用形成的碳汇量。

英文摘要：

Stable carbon isotope is a useful and powerful tool for tracing the origin and transformation of carbon in karst dynamics system. For obtaining the characteristics of hydrochemistry and isotope, groundwater samples in wet and dry seasons from 63 karst subterranean streams in Chongqing are collected in this study. The results show that the HCO3- is the dominant species of the DIC in ground waters and the concentration of HCO3 is lower in wet season than dry season due to dilution.δ13C--DIC （V-PDB） in karst subterranean streams in Chongqing varies from -15.34 %-5.89 ‰ in dry season and from -17.40‰-4.23 ‰ in wet season. The widely variations of δ13C in wet season show the complex origins of carbon in karst subterranean streams in wet season. Based on the δ13C isotope mass balance equation, the amount of DIC that comes from the carbonate rock dissolution is calculated in this study. The calculated results show that 45.1 -79.7 %of the DIC in the dry season and 34.6%-82.1 % in the wet season is from dissolution of carbonate rocks in karst groundwater. The calculated results also shows that the DIC and the corresponding δ13C proportion originated from the carbonate rock dissolution is not necessarily 50 % according to the molar ration of karst chemical reaction equation, but has a changes range at some extend. As a result, this study suggests that we should deduct first the DIC originated from the carbonate rock dissolution using the δ13C when we calculate the carbon sink of karst processes, and then calculate further the karst carbon sink.