Study On The Geochemical Processes And Environmental Significance From The Element Migration Through Out The Furong Cave System, Chongqing, China

In recent years there has been an important alternative indicator in cave speleothems as archives of paleoclimate change of the karsts area. Drip water chemical components are directly originated from bedrock and soil overling cave, also they are the important library of materials in speleothems. Also precipitation determines the content of the various elements of speleothems in the transport processes which is the soil and bedrock in the role of physical, chemical and biochemical. Based on studying of the sources of elements about drip water and sediments, and migration mechanism in various karst geochemical process, it was the use of many elements characteristic stalagmite indicate the past environmental change. It was the differences on the biogeochemical cycle of substance in different climate conditions of different regions and different soil environments. The element value or the ratio which is between the drip water, speleothems and the local precipitation had complex relationship. In further work all of them were needed to elucidate the true meaning.In this study, based on element analyzing of bedrock and soil, and system monitoring on water geochemistry(including pH, main ions etc.) in spring water, soil infiltrating water and drip water to understand the mechanisms of formation of drip water with environment overlying processes which response to the climate change out/in Furong cave, Chongqing, China. A number of conclusions have been achieved as shown below.1) It was found that the concentration of Ca2+, Mg2+, Sr2+ and SO42- had obvious differentiation in the process of migration among different phases of bedrock, soil and water in epikarst ecosystem. As the mass source of soil, element composition of bedrock had considerable influence on the element content of soil, soil infiltrating water and cave drip water. Additionally, the elements had mainly transfer for the Ca and Mg which is the dolomite in the carbonate-based bedrock out Furong cave, and influence on the migration or accumulation of other elements. Also the environment for the concentration of elements had obvious differentiation in soil profile is consistent with the dominated by dolomite bedrock.2) Contents of Ca, Mg and Sr in the soil profiles showed significant evidence of leaching and deposition, which had increased with depth of the main rock components and contents of trace elements and it had direct control over the concentration of corresponding element in soil infiltrating water. When the precipitation through the thin soil, lesser dissolved substances in the soil and increase the contribution of bedrock to chemical composition of drip. It had the directly or indirectly affect to the chemical characteristics of drip water about the thickness of overburden, soil physical, chemical and biological processes, the thickness of bedrock, karst water in the bedrock of the migration pathway and the time of water-rock interaction and so on.3) Precipitation, intensity and frequency of rainfall will influence on rainfall replenishment of this supply of cave water, which caused the differences on surface infiltration rate, rainfall through the aperture of the pores at all levels or cracks.4) The pH of cave drip had a bit more alkaline which would be larger in the dry season, and smaller varying in the rainy season. The concentration of Ca2+, Mg2+ and Sr2+ had obvious ranges in the six sites, it is showed that there were a consistent hydrochemical characteristics of cave water in the process of migration among different phases of bedrock and soil. Different migration paths and retention time of different drip sites have lead to different concentration of SO42-. The characteristics of Mg/Ca and Sr/Ca ratios in drip water indicated that the dry season be larger the rainy season, and both of these associated with the precipitation. In addition the ratios reflected the pre-deposition of the Ca2+ during the dry season.5) Through system monitoring to the hydrochemical characteristics about springs, soil infiltrating water and cave drip water, it is found that there are different variation ranges among the three types of water in epikarst ecosystem. In addition the elements concentration of different kinds of water almost changed simultaneously and coordinately with the seasonal variation:the amplitude of concentration of Ca2+, Mg2+ and Sr2+ would be larger in a dry season, while smaller in the rainy season, the amplitude of concentration of SO42- didn't have such characteristic. Thus different migration paths, time and environmental conditions of different drip points have lead to different response to precipitation.It is the important effect of elements migration under the control of dynamics system of the epikarst zone. Affected by differences of migration paths, environmental temperature, precipitation, humidity and other conditions, an understanding of temporal and spatial variability of the element migration showed complex changes in the process of physical, chemical and biochemical. Because of the diversity of transfer route, resort period, and environmental conditions for different drip water in cave, geochemical characteristics of multi elements and the relationship between element content and environmental factors should be investigated systemically in the reconstruction of environmental change out of cave by utilizing the variation of geochemical proxies from speleothems.