Analyzing The δ¹³ C_DIC Variability Characteristics And Influencing Factors Of Cave Drip Water Under The Different Rocky Desertification

Rocky desertification in karst areas is regarded as fragile as the surrounding ecological environment of deserts. Under the condition of tropical, subtropical, humid, semi-humid climate of karst, rocky desertification is extremely developed, and is disturbed by human activities. It brings about vegetation destruction, serious soil erosion, a large area of bare bedrock, land degradation, and other secondary geological disasters, such as flash floods, landslides and mudslides. The carbon cycle is an important part in the process of karstification. we monitor cave pH value, electrical conductivity (EC), HCO3_, Saturation Index of Calcite(Slc), concentration of Ca2+,Mg2+and carbon dioxide partial pressure of caves in order to evaluate carbon sink and research climate change accurately.Guizhou Province is located in the heart of karst area in southwest China, where the serious rocky desertification endanger the ecological environment and economic development. Although some measures have been carried out to control the rocky desertification and have achieved initial success, the management of rocky desertification is not satisfactory. Therefore, researching the reason and evolution of rocky desertification is particularly important. We analyze the variability of δ13CDIC and surface environmental information by the modern monitoring in rocky desertification area to understand the mechanism of rocky desertification and provide a theoretical basis for controlling rocky desertification.The major research objects of study are different rocky desertification karst caves(the Shijiangjun Cave and the Benzhai Cave) in the central Guizhou plateau surface, Xixiu of Anshun City in Central Guizhou Province. Continuous monitoring of cave environment, chemical characteristics of drip water in two caves and δ13CDIC test were gone on from October2010to December2011. Through analyzing modern monitoring for two adjacent caves, we discuss about the relationship between δ13CDIC of dripping water and overlying vegetation to find out the response mechanism of the modern environment so that to provide a theoretical basis to study the rocky desertification mechanism. At the same time, we make a simple discussion on the possible driving mechanism of the carbon cycle and its karst carbon sinks and draw the following conclusions:(1)Comparing the chemical characteristics of the two caves, it shows that:because of the different rocky desertification level of the Benzhai Cave and the Shijiangjun Cave and there are more plants upper Benzhai Cave than Shijiangjun Cave, the CO2released by plant respiration is very important for carbon cycle in kast areas, although it produces little effect on δ13CDIC of dripping water. Conductivity and Ca2+concentrations of dripping water in the Benzhai Cave are higher than the Shijiangjun Cave, for the participation of surface plants. Therefore, finding the mode of production for changing strength of karst carbon sink in the rocky desertification region not only improves the ecological environment of the rocky desertification region, but also produces important effect on the study of global carbon cycle research.(2) Following the drip rate variation,8dripping points of the Shijiangjun Cave and7dripping points of the Benzhai Cave are divided into the changeable type and stable type. There is little correlation between drip speed and δ13CDIC in the Shijiangjun Cave and Benzhai Cave. Because dropping speed maybe not the most important factor of δ13CDIC variation, in another word, the cave roof thickness have no direct impact on δ13CDIC value of dripping water.(3) Contrasting the variation of δ13CDIC from dripping water between Shijiangjun Cave (the intense rocky desertification) and Benzhai Cave (the potential-mild rocky desertification), we found that it shows the same trend:The δ13CDIC tends to be lower in the whole dry season, however, it fluctuates greatly in rainy season. From October2010to April2011, the δ13CDIC of Shijiangjun Cave became lower and lower. This is because that the Shijiangjun Cave belong to intense rocky desertification, and there is little soil and vegetation. The temperature became lower and the plants and microbial activity weaken in October, while the rainfall still large. The light carbon from plants and microorganisms is washed away by the rain. It is the reason that the813CDIC was not low in the late period of rainy season. The δ13CDIC of8dripping points in Shijiangjun Cave become so high may be associated with freezing rain in January. In the rainy season,δ13CDIC value fluctuates greatly each month in the Shijiangjun Cave and the Benzhai Cave, and they did not present a low or high trend as the dry season. The collective effect of rainfall and evaporation may be the main factor, which controls the variation of δ13CDIC in the rocky desertification region during the rainy season.(4) The impact of vegetation variation is less important for δ13CDIC than evaporation and other factors. The light carbon from plants may be affected by environment because there is little soil upper the cave. And from atmospheric precipitation to dripping water, the δ13CDIC is affected easily by many factors, which contribution to813CDic differently in different environment.In summary, comparing the features of δ13CDIC and analyzing the influence factors in different rocky desertification areas, we find that:the minimal amount of soil, the uneven spatial distribution, precipitation, evaporation, and many other factors are influential to δ13CDIC in rocky desertification regions. When we use813C to interpret the change of environment, we have to consider the difference in different areas in order to determine the factors controlling δ13CDIC accurately and find a theory to explore the rocky desertification.