Characteristics of cave drip water and modern carbonate (CaCO3) deposits caused by underground river artificial recharge and landscape restoration

The landscape of carbonate (CaCO3) deposits in the karst tourism caves is susceptible to pollution and weathering on carbonate sediments. To ensure the sustainable development of the karst tourism caves, it is necessary to study the methods to repair such contaminated or damaged sediments in these caves. To attain this purpose, continuous monitoring and analysis for four years were made to chemical properties of the underground river, cave drips, and modern carbonate sediments in the No.15 branching cave of Seven Star Cave, Guilin, Guangxi Province. The results show that the change trends of conductivity, Ca2+ and HCO3- from the underground river and cave drip water are basically the same during this period. The conductivity, Ca2+ and HCO3- of cave drip water decreased significantly and the rainfall dilution effect is obvious during rainfall seasons. The modern carbonate (CaCO3) deposits in the cave have obvious seasonal variations, where cave drip water amount, drip rate and calcium carbonate deposit rate during rainy seasons accelerate. The largest amount of deposit is 0.8 g/ half month. The largest amount of calcium carbonate deposit from rapid drip water from the cave entrance to about 150 m within the cave passage is up to 2-4 g/half month. The carbonate deposit rate during dry seasons reduces with the maximum only 0.4 g half month. The recharge of cave drip water by extracting the karst underground river can enhance the conductivity, [Ca2+], [HCO3-] and CaCO3 saturation of cave drip water, rapidly prompting a large number of carbonate (CaCO3) deposits, and realizing restoration of the cave landscape damaged. Besides, new calcium carbonate deposit can also rebind bedrock fissures and damaged / broken speleothem and cave stalactites, which is favorable for the stability of the cave.