| 其他摘要 | River is the most essential way to connect the ocean with the terrestrial environments. The research on river is the crucial aspect of the global carbon cycling research. Therefore, the geohydrochemistry research of river is the vital method to trace the drainage erosion, weathering and element cycling among the terrestrial system, river and ocean. The main cations and anions from the carbonate weathering dominate the construction of the ions in the surface river. Hence, it plays a pivotal role in researching on the geohydrochemical character of the surface river in the carbonate drainage area for understanding the controlling factors of the erosion, weathering intensity, geochemical construction of river.
The research of the geohydrochemical character in Pearl River is limited and only concentrates on the monitoring of the climate change in pearl drainage area, migration of the organic pollutant in the river and isotope tracing in the Pearl River delta and estuarine river. However, there is nearly no systematical research on a large multitude of branch rivers of Pearl river, especially in the typical climatic and geological area. In fact, it is very essential to research on the geohydrochemical character and drainage erosion with the isotopic tracing method in the small branch rivers in Xijiang drainage area systematically, which is the main branch of Pearl River, owing to the geographic particularity such as morphological characteristics, soil, climate and vegetation. This research has a great contribution both to the geochemical characters of the chemical weathering and erosion of the rock and soil and environmental pollution in the typical Karst region, SW China, and to the systematical research on the global cycling of carbon.
This research was supported by the 973 National Programme on Key Basic Research Project- Stone Desertification and Ecological System Regulation in typical Karst drainage basin, SW China. This thesis analyzed the geohydrochemical character and carbon isotope geochemical character of the surface water in the different types of vegetation both in metamorphic clasolite area and marine face carbonate rocks area in Xijiang drainage area, Guizhou province and addressed some main conclusions as follows:
1. The lithologic features in the Xijiang drainage area were the crucial controlling factors of the geohydrochemical character of the surface water and the weathering erosion intensity. The pollution in the rivers from the human activities had some effects on the ion construction of the surface water as well.
2. The main resources of the surface water in the research area were rainwater and groundwater. Rainfall was more frequent in this period of time affected by Southwest Monsoon. Most of rainwater passed through the surface soil, and enter the aquifer of deep water. Then the rainwater might enter the open river as the direct surface runoff or took part in the cycling of groundwater. The surface water net and groundwater net were interconnected because of the frequent faulted structure in NNE direction; hence, the conversion between surface water and groundwater was very frequent.
3. The ion compositions and the physical and chemical properties of the surface water in this research area were controlled by the chemical weathering process of soil and rocks. The lithologic feather of bedrocks in different drainage area led to the big difference in ion concentration and geohydrochemical features of surface water.
4. It was found that DIC in the surface water of this research area derived from the chemical weathering of silicate and carbonate by soil CO2, based on the concentrations and carbon isotope analysis of DIC, DOC and POC in 75 surface water samples of Pearl River in Guizhou province. Generally speaking, the richer of the soil CO2 in the research area with better vegetational cover, the more intensive of the chemical weathering. The chemical weathering was easier to occur in carbonate than in silicate and the product of chemical weathering could change the ion compositions and the characters of surface water.
5. The organic carbon in the surface water was related to the type of vegetation in the drainage area. The concentration of DOC in surface water could reflect the types of vegetation and the rate of vegetational cover. The concentration of TSS and POC could illustrate the situation of organic matters in the soil of drainage area. The concentration of DOC and POC in surface water could help to distinguish the source and sink of carbon in Karst drainage area and to set up the carbon cycling model.
6. POC from the suspended matters in surface water, derived from soil organic matters and terraneous vegetation, was the crucial proxy of drainage erosion. The value of δ13CPOC had the inverse correlation with the ratio of TOC/TN in the surface water of research area; hence，POC in the surface water was probably coming from the deep soil in drainage area. The lower ratio of TOC/TN was with the stronger hydropower and more intensive drainage erosion. |
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