| Recently, research of global change is getting more and more concerns from the international community. Problems as temperature rise, sea level ascend which were probably caused by atmospheric greenhouse gases have been put into the government agenda with economic development goals around nations. The fact of climate change and the actual influence of human being are in the centre of the climate change debate. Continuous meteorological variation and atmospheric CO2 variation recorded by instruments are limited, for the history of human being is so short in the earth evolution. The time horizon of instrumental record can not reveal the regularity of the long term climate change and the impact of industrialization. Therefore, geological record plays an essential role in revealing the regularity of palaeoclimate. Secondary sediment in cave karst dynamic system is an important geological record carrier of palaeoclimte, we can benefit in interpreting the environmental information of speleothems through the research.This research aimed at nourishing karst dynamics practice, and had been guided by karst dynamic system theory. It took more than a whole hydrological year to run the monitoring work on carbon water and calcium in the research system (Xueyu Cave). Different phases (solid, liquid and gas) environmental variable had been involved as the index, which included system CO2, water kinetic condition, hydrogeochemistry, dynamic temperature and humidity, calcite deposition rate, and stable carbon and oxygen isotopes. According to the data analysis, conclusions can be made as below:(1)The operation process of Xueyu cave KDS can be easily influenced by the outer environment, and it has significant seasonality. As a driving force of the dynamic system, CO2 can sensibly respond the variation of temperature and rainfall, and the reason is the rapid water exchange between ground and underground. Although the respiration of human can induce temporary CO2 variation, the system CO2 self adjustment dominated by the underground river is the main function in seasons or a longer time scale.(2)As the output of KDS, calcite sediment amount varied seasonally with the syetem operating. Significant difference of seasonal environmental CO2 and water kinetic condition change are the reason of drip water deposition rate variation in Xueyu cave. Since the unique composition and homogeneous crystal structure of the calcite sediments, the seasonal variation of deposition rate did not lead the sediments to laminar fabric. The spatial element ratio variation indicated that the underground river deposition process is mainly controlled by the water kinetic condition (current velocity and flow thickness), except the cave environmental CO2 alteration period(April and November), in which deposition process is definitely influenced by degassing or dissolving effect.(3)The stable carbon isotope values varied with a significant seasonal and spatial characteristic in Xueyu cave, for KDS here is heavily inflenced by the upper biological agent. Although rainfall stable oxygen isotope values varied according to the seasons, the mixing effect of the upper aquifer and the interference of bed rock oxygen isotope might obscure the seasonality, and the variational magnitude of the stable oxygen isotope value was comparatively small during the year.Biocatalysis in calcite deposition process was firstly involved in this study. The measurement of organic amino acids molecules content in drip water indicated a significant biological effect, but the low magnesium cave background did not leave too much room for organic molecules to join in the calcite deposition process. The biocatalysis effect is even slighter than the common ion effect caused by gypsum dissolution.
|
PDF Full Text Request