不同植被条件下岩溶地下水δ13CDIC的差异研究——以贵州夜郎洞、天钟洞和普定岩溶水碳通量模拟试验场为例

STUDY ON THE DIFFERENCE IN δ13CDIC OF KARST GROUNDWATER UNDER DIFFERENT CONDITIONS OF VEGETATION——EXAMPLES FROM YELANG CAVE, TIANZHONG CAVE AND PUDING SIMULATION TEST SITE

影响石笋δ13C的因素众多,且其中一些影响机制未知,从而导致利用石笋δ13C准确重建古环境仍存在一定的困难.作为形成石笋母液的洞穴滴水,其δ13CDIC变化必然会导致石笋δ13C的变化,因而只有对影响洞穴滴水δ13CDIC的各种因素进行细致的研究才能更好地利用石笋δ13C重建古气候环境.对贵州夜郎洞、天钟洞和普定岩溶模拟试验场的研究均表明,雨季上覆植被生物量的大小以及植被类型（C3和C4）是控制岩溶地下水δ13CDIC变化的主要因素.而对于夜郎洞的研究还得出旱季先期CO2脱气作用对岩溶地下水δ13CDIC的影响较大,如夜郎洞C3植被下雨季δ13CDIC值在-10.94‰～-12.15‰之间,旱季为-3.66‰～-5.50‰,夜郎洞C3植被下滴水点雨季旱季之间差异最大达到-8.49‰,这些不仅仅是由生物量的变化而引起的,先期CO2脱气对滴水碳同位素的影响也是不可忽略的.不同于夜郎洞旱季滴水δ13CDIC,先期CO2脱气作用对天钟洞滴水δ13CDIC的影响较小,天钟洞滴水δ13CDIC总体上能够反映上覆植被发育状况,因而先期CO2脱气作用等过程对滴水δ13CDIC影响因洞穴而异,可能反映了洞穴顶部包气带不同水文地质条件的影响.

There are many factors influencing the δ13CDIC values of speleothems and some influencing mechanisms are still unknown. Therefore, it is difficult to reconstruct the paleoenvironment by using the speleothem δ13CDIC values. As the mother solution of speleothem, the variations of the δ13CDIC of dripwater must lead to the variations of speleothem δ13CDIC. Therefore, only by doing more detailed study on the factors influencing the δ13CDIC of drip water, can one reconstruct more correctly the paleoenvironment by using of the speleothem δ13CDIC 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 （C3 or C4） controlled the 813Coic of the karst groundwater during rainy season, while prior CO2 degassing showed more impact on the δ13CDIC during the dry season. The study in Yelang Cave also shows that prior CO2 degassing showed more impact on the δ13CDIC during the dry season. Taken the dripping site below the C3 vegetation as an example, the δ13CDIC ranged from -10.94‰ to -12.15‰ in the rainy season, and -3.66‰ to -5.50‰ in the dry season. The biggest difference between the rainy and dry season was up to -8.49‰, which was caused by not only the change of biomass, but also the prior CO2 degassing. However, different from the ease in Yelang Cave, the prior CO2 degassing showed less impact on the δ13CDIC of dripwater in Tianzhong Cave during dry season. This indicate that depending on the difference in hydrogeological conditions, prior CO2 degassing may show different behavior between different karst systems.