The regolith effect on carbon transfer path in epi-karst system

In order to understand the mechanism of karst carbon sink, it is necessary to get clear the carbon transfer path among the materials in the three phases of air, solid carbonate rocks and liquid karst groundwater in epi-karst system. There are 8 carbon stable isotope sample sites, including 5 groundwater sites and 3 gaseous CO2 sites in the Banzhai Undergroung River Catchment. Based on the analysis to carbon stable isotope and CO2 partial pressure data, it is found that the carbon in free air and karst water mostly come from the soil air. The carbon transfer path in epi-karst system can be divided into 4 steps: (1) the photosynthesis of vegetation taking CO2 from free air; (2) release of CO2 to the soil layer by way of the respiration of plant roots and decomposition of humus; (3) the gaseous CO2 being transferred to liquid HCO3- ion by karst process during the water cycle; (4) the bicarbonate in groundwater moving to river or ocean with the groundwater flow. The forest and soil takes a “booster pump” action to increase the soil CO2 partial pressure from free air and raise the rate of karst process remarkably, it also plays a very important roles in karst process carbon sink.