Study on diurnal change of physic-chemistry of karst spring of epikarst system

Mt.Jinfo,a karst dynamic system monitoring site,lies in Nanchuan city,Chongqing province.The data from the site's automatic records(CTDP300) indicates that the karst dynamic system is highly sensitive to the environment.The physico-chemical variation of the epikarst spring water is quite different under different climatic condition.In normal days without rainfall,water temperature and air temperature have the same variation,and its peak zone lags behind the top temperature for several hours.This is probably attributed to the gradient of CO₂ concentration in atmosphere caused by the conversation of vegetation from photosynthesis,which is helpful to the karst process.Furthermore there is difference in the time behind the top temperature because of the vegetation cover and the geographical structure.At the beginning of a rainstorm,the physico-chemical variation of spring is mainly controlled by the dilute effect with the adjusting of vegetation and soil.It can last for the entire rainfall process,but several hours later,the hydrodynamic effect and the CO₂ effect will occupy the dominant position due to the high fissure rate and permeability in epikarst zone.So it is necessary to explain the hydrochemical behavior of epikarst process in the water-rock-CO₂ system.