Dissolved inorganic carbon and stable carbon isotope in karst subterranean streams in Chongqing , China

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 63karst subterranean streams in Chongqing are collected in this study.The results show that the HCO 3 is the dominant species of the DIC in ground waters and the concentration of HCO 3 is lower in wet season than dry season due to dilution.δ 13 C-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 ofδ 13 C in wet season show the complex origins of carbon in karst subterranean streams in wet season.Based on theδ 1 3 C 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 δ 13 C 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 theδ 13 C when we calculate the carbon sink of karst processes,and then calculate further the karst carbon sink.