Tracing The Migration And Changes Of DOM Under The Karst Underground River By Fatty Acids

Karst carbon sink is of great signality in karst area of Southwest China, and 0.2 billion tons atmospheric CO2 carbon sink are fixed by karstification. However, carbon sequestration produced by karstification hasn’t been widely identitied up to now. In recent years, it is found from the studies that aquatic plants can absorb the DIC dissolved into waters by photosynthesis. When aquatic plants are putrefaction and decomposition, part of them may be stored in waters in the form of DOM and other forms of organic carbons. And being the largest organic carbon pool, DOM also plays an important role in global carbon cycle and linking the process between land aquatic ecosystems. Although most DOM is easily degraded, there’s still a part of DOM that can resist degration and be the long-term carbon sink. In addition, HCO3- in karst underground river can not only be absorbed by microorganism through photosynthesis, but also it can be utilized by nonphotosynthesis microorganism, which increases the microorganism carbon sink.When the DOM that comes from the land surface, especially lake aquatic plants, flows into the karst underground river with the water, since the yearly variation of water temperature is of little difference and avoid of light, combined with the effects of non-photosynthetic microbial flora function, which makes it of great significance in studying the sources, migration and changes of DOM under karst underground river. DOM has various sources and it also has different molecular structures, which forms a challenge in discussing the migration and changing of DOM in underground river. Biomarker(fatty acids, alkanes, sterols, and etc.) can characterize the source of organic matter, record and store the information of organic sources, which plays an important role in tracing the sources and the changing characteristic of DOM during the migration process. In this study, Qingmuguan underground river watershed was selected as the study object, and discussed the source, the changing influence factors of DOM during the process of migration by utilizing fatty acids and water physical properties.(1)Dissolved fatty acids contents in Qingmuguan underground river was decreased by the increasing distance of migration. Dissolved fatty acids contents were predominated by saturate straight fatty acids, followed by monounsaturated fatty acids, polyunsaturated fatty acids. In addition, dissolved fatty acids contents in Qingmuguan underground river was influenced by precipitation. During rainy seasons, dissolved fatty acids contents in Qing mugan underground river were mainly from the organic matter which came from headwater storage reservoir through Yankou sinkhole, and the monthly contents of dissolved fatty acids Changed significantly. During dry seasons, the dissolved fatty acids were controlled by the supply of fissure water, and the monthly contents of dissolved fatty acids Changed slightly.(2)By PCA method, the source of dissolved fatty acids among different sampling site in Qingmuguan underground river were discussed. In Yan kou spring, dissolved fatty acids mainly came from autogenous sources, followed by exogenous sources. Alga, microorganism(bacterial, fungi and etc.) constituted the major source of DOM, but its contents were mainly controlled by biological activities. In Jiang jia long dong spring and Jiangjiaquan spring, the source of dissolved fatty acids contents was mainly not only controlled by the organic matter which came from headwater storage reservoir, but it also received the organic matter from the land surface during the migration of underground river.(3)The degradation degree of DOM in Qingmuguan underground river was studied by the CPI ratios and water phusical proteries. It was found that during the dry seasons, the DOM was highly degraded because of the long migration distance from the surface to underground river. However, in rainy seasons, the DOM was lighly degraded, which was resulted from the short migration distance of DOM in underground river. The migration and changing characteristic of DOM among different sources was similar, but the causing factors that influences the migration and changing characteristic of DOM were different. For example, dissolved fatty acids content(alga, bacteria or other microorganism) was mainly controlled by temperature variation. Dissolved fatty acids contents from land higher plants in the migration of underground river was mainly influenced by degradation activities, in addition, rainfall also had important role in influencing the contents of dissolved fatty acids.(4)Rainfall can influence the input characteristic of dissolved fatty acids among different sources in underground river. During the precipitation, low carbon fatty acids in surface soil were washed out of the soil and been transported into the underground water, resulting in the increasing contents of fatty acids from alga, bacteria and other microorganism, but the fatty acids contents from aquatic plants and land higher plants was relative decreased. During dry seasons, the fatty acids content(aquatic plants and land higher plants) was relative increased.