STUDY ON THE DIFFERENCE IN delta~(13)C_(DIC) OF KARST GROUNDWATER UNDER DIFFERENT CONDITIONS OF VEGETATIONEXAMPLES FROM YELANG CAVE, TIANZHONG CAVE AND PUDING SIMULATION TEST SITE
There are many factors influencing the delta~(13)C values of speleothems and some influencing mechanisms are still unknown. Therefore, it is difficult to reconstruct the paleoenvironment by using the speleothem delta~(13)C values. As the mother solution of speleothem, the variations of the delta~(13)C_(DIC) of dripwater must lead to the variations of speleothem delta~(13)C. Therefore, only by doing more detailed study on the factors influencing the delta~(13)C_(DIC) of drip water, can one reconstruct more correctly the paleoenvironment by using of the speleothem delta~(13)C values. This paper chose the Yelang Cave (26°02'N, 105°44'E, altitudes 1285m) , Tianzhong Cave (25°07'N, 108°18'E, altitudes 758.8m) and Puding Simulation Test Site (26°26'N, 105°27'E, altitudes 1200m) as examples to conduct such a study. It shows that biomass above the cave and vegetation type ( C_3 or C_4) controlled the delta~(13)C_(DIC) of the karst groundwater during rainy season, while prior C0_2 degassing showed more impact on the delta~(13)C_(DIC) during the dry season. The study in Yelang Cave also shows that prior C0_2 degassing showed more impact on the delta~(13)C_(DIC) during the dry season. Taken the dripping site below the C_3 vegetation as an example, the delta~(13)C_(DIC) ranged from - 10.94%o to -12.15%o in the rainy season, and -3.66%o to -5.50%o in the dry season. The biggest difference between the rainy and dry season was up to -8.49%o, which was caused by not only the change of biomass, but also the prior C0_2 degassing. However, different from the case in Yelang Cave, the prior C0_2 degassing showed less impact on the delta~(13)C_(DIC) of dripwater in Tianzhong Cave during dry season. This indicate that depending on the difference in hydrogeological conditions, prior C0_2 degassing may show different behavior between different karst systems.