Hydrological characteristics of dripping water in karst caves under different land covers
In recent years,the deterioration of global climate has caused a series of natural environment problems,which urgently requires researchers to forecast the future climate and put forward effective management measures.Previous studies have shown that the study and reconstruction of the earth paleoclimate can help people understand the patterns of past climate change and its dominant mechanism.Therefore,as to effectively predict the future climate change and the way the contemporary ecosystem responds to the future climate change,the restoration and reconstruction of ancient climate and environment have gradually become the focus of today's research on earth sciences.At present,an increasing number of researchers have reconstructed paleoclimate and environment based on various geochemical indexes of stalagmites and secondary carbonate sediments in karst caves.Cave dripping water is the material basis for the formation of stalagmites,and it is also the main source of trace elements in stalagmites.The high frequency signal caused by the change of external climate environment will affect the ancient climate information recorded by stalagmites.Therefore,it is of great importance to establish a long-term monitoring system based on cave dripping water and to analyze the relationship between the hydrologic characteristics of cave dripping water and the changes of external environment during the study of stalagmite indication.Cave dripping water is an important part in the water cycles of karst areas,and its hydrological characteristics are closely related to the geochemical isotope indexes which carry climate information.The land cover type is an important factor affecting the regional water cycle processes.However,most of the current studies discussing the impact of land cover on water cycle processes are mainly concentrated on the watershed scale in non-karst areas,and very few studies focus on the impact of land cover on the hydrological characteristics of cave dripping water in karst areas.In order to explore the influence of different land covers on hydrological characteristics of cave dripping water in karst areas,this study selected three karst caves with different types of topsoil and vegetation in Guizhou Province,Southwest of China.These three caves are Qingjiang cave with thick soil layer and moderate vegetation cover),Guangshun cave with thin soil layer and dense vegetation cover,and Shijiangjun cave with thin soil layer,sparse vegetation cover and thick carbonate roof.This study was conducted based on drip discharge rate,soil water content and meteorological data during one hydrological year.Study results show:(1)The drip discharge rates of the three caves display obvious seasonal variations that are synchronized with the input of precipitation,i.e.high in the rainy season,low in the dry season,because they were influenced by meteorological conditions,e.g.precipitation,temperature and humidity.The dripping water flow is vulnerable to dry up in the dry season with less precipitation input.(2)Soil has a strong retention and storage effect on precipitation infiltration.Compared with Guangshun cave and Shijiangjun cave,Qingjiang cave with thick soil layer on the roof shows a unique low flow value during the rainy season from August to October,due to high external temperature and long exposure time after rain,which leads to strong evaporation effect.Besides,the lowest annual soil water content also occurs during this period.(3)The abundance of drip discharge rates of the three caves can be ranked as follows:Shijiangjun cave(1.185 mL·min-1)＞Qingjiang cave(0.600 mL·min-1)＞GGuangshun cave(0.236 mL·min-1),according to their annual mean values.The annual stability of their drip discharge can be obtained by their Cv values,indicating that the drip discharge is the most stable in Shijiangjun cave(0.072),followed by the discharge in Guangshun cave(0.481)and Qingjiang cave(1.264).(4)The influence of vegetation on hydrological characteristics of dripping water is weaker than that of soil,and the dripping water flow in caves with better soil cover development are more likely to dry up throughout the year.For example,the dripping water flow in Qingjiang cave with thick soil cover is more likely to dry up than in Guangshun cave with thin soil layer but with dense vegetation cover.In addition,caves with thick carbonate roof would have a better regulation effect on dripping water flow,e.g.Shijiangjun cave where its dripping water flow is the most stable and abundant throughout the year.In summary,the discharge rate of dripping water is affected not only by meteorological conditions such as precipitation,temperature and humidity,but also by land cover and thickness of aquifer roof above a cave.Therefore,the results of this study could provide crucial scientific guidance for the selection of dripping water points with relatively abundant and stable flow in karst caves,and would be of great significance for the use of cave dripping water in climate research.
land coverdripping waterhydrological characteristicsdischarge ratesoil water content
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