| 贵州碳酸盐岩风化壳剖面元素和同位素特征及碳汇效应 | |
| 李道静 | |
| Thesis Advisor | 季宏兵 |
| 2014 | |
| Degree Grantor | 中国科学院研究生院 |
| Place of Conferral | 北京 |
| Degree Name | 博士 |
| Degree Discipline | 地球化学 |
| Keyword | 碳酸盐岩风化壳剖面 硅酸盐岩风化壳剖面 化学风化 碳循环 稳定碳氧同位素 放射性碳同位素 |
| Abstract | 本文选择位于贵州省的四个碳酸盐岩风化壳剖面，以硅酸盐岩风化壳剖面作为对比，通过风化剖面中的元素变化，计算碳酸盐岩与硅酸盐岩风化过程中CO2的消耗量，了解碳酸盐岩在碳循环上的系统调控规律。同时还分析了碳酸盐岩风化壳剖面中碳氧同位素的演化特征以及与区域气候之间的关系。 风化剖面主量元素的分析结果表明，碳酸盐岩的风化作用主要发生在岩-土界面，为碳酸盐矿物的快速溶蚀过程，伴随着大量活泼元素（主要是Ca、Mg、Na、K）的淋失，这期间单位体积碳酸盐岩对CO2的消耗量约是硅酸盐岩风化剖面的4倍。碳酸盐岩风化过程的后期主要为酸不溶物的继续风化过程，由于大量元素的流失，此过程中单位体积碳酸盐岩风化壳CO2消耗量约是硅酸盐岩风化壳的十到千分之一倍，但仍然可以说明，碳酸盐岩的化学风化过程同硅酸盐岩一样能产生净碳汇。 在碳酸盐岩风化壳剖面中，土壤有机质稳定碳同位素（δ13CSOM）分析结果表明，C3与C4植物共存。土壤SEM扫描结果以及土壤中分散态碳酸盐稳定碳同位素值（δ13CSC）表明土壤中的碳酸盐以次生碳酸盐为主，其形成主要与根系活动有关。对于多数样品，通过δ13CSOM估算的次生碳酸盐的δ13C值（δ13CPC）高于δ13CSC，说明次生碳酸盐形成期间C3植物所占比例相比现今更高。贵州省西部地区相比中部地区，气候上的差异表现为西部的降雨量较小、雨期较短、雨水分布不均、年均温度较低，最终导致碳酸盐岩风化壳剖面中土壤碳酸盐的碳氧同位素（δ13CSC 和δ18OSC）值西部的更高，正相关性也更高。然而气候因素的影响却不能解释硅酸盐岩风化壳剖面中δ13CSC 和δ18OSC在不同剖面中的差异，土壤碳酸盐的稳定碳氧同位素比值有可能还受到岩石类型、植被类型等其他因素的影响。研究还发现δ13CSC与化学蚀变指数CIA之间存在一定的负相关关系，这与土壤中次生碳酸盐的形成过程有关。因此δ13CSC有可能成为判断剖面风化程度的指标之一，但同时也受到除了风化作用以外的其他因素影响。 土壤有机质放射性碳同位素的分析结果表明，有机质的平均驻留时间在所研究的剖面中由上自下逐渐增大，土壤有机质分解产生的CO2通量上层土壤高于小层土壤，反应了土壤剖面自上而下发育过程中有机质形成及更新的规律。受到人为种植农作物影响较大的剖面表层土壤有机质更新较快，因此表层土壤有机质分解产生的CO2通量远远大于其他剖面。相对于森林土壤，所研究区域的土壤储存碳的时间尺度更长。 |
| Other Abstract | To understand the roles of carbonate rocks in carbon cycle, four carbonate profiles in Guizhou Province were selected and compared with silicate profiles in CO2 consumption calculated based on elemental changes in the profiles. The carbon and oxgen isotopic value in the carbonate profiles was also studied and related to the local climate. The major elemental results demonstrate that the chemical weathering reaction of carbonate rocks mainly happened at the rock-regolith interface, with quick dissolution of carbonate minerals and great leaching of active elements (Ca, Mg, Na, K). During this process, the CO2 consumption per volume of carbonate rocks was about 4 times larger than that of silicate profiles. During the further weathering process of the insoluble residuas on carbonate rocks, the CO2 consumption per volume of silicate regolith was about tens to hundreds times larger than that of carbonate regolith because most active elements had been lost in the carbonate regolith. However, it implies that chemical weathering of carbonate rocks can produce net carbon sink as well as silicate rocks. To understand the roles of carbonate rocks in carbon cycle, four weathering profiles devoloped on carbonate rocks in Guizhou Province were selected and compared with that on silicate rocks.The CO2 consumption were calculated based on elemental changes in the profiles. The carbon and oxgen isotopic values in the carbonate weathering profiles were also studied and related to the local climate. The major elemental results demonstrate that the chemical weathering reaction of carbonate rocks mainly happened at the rock-regolith interface, with quick dissolution of carbonate minerals and great leaching of active elements (Ca, Mg, Na, K). During this process, the CO2 consumption per volume of carbonate rocks was about 4 times larger than that of silicate weathering profiles. During the further weathering process of the insoluble residuas on carbonate rocks, the CO2 consumption per volume of carbonate regolith was about tens to thousands times smaller than that of silicate regolith because most active elements had been lost in the carbonate regolith. However, it implies that chemical weathering of carbonate rocks can produce net carbon sink as well as silicate rocks. At carbonate weathering profiles, the δ13C values of soil organic matter (δ13CSOM) reflect a coexistence of C3 and C4 plants. The soil SEM observation and the δ13C value of soil disseminated carbonate (δ13CSC) demonstrate that the soil carbonate is dominant by pedogenic carbonate, and its formation is closely associated with root activities. The estimated δ13C value of pedogenic carbonate (δ13CPC) based on δ13CSOM is higher than δ13CSC, suggests that the C3 plant take a larger percent when carbonate precipitated. The different climate conditions in the west compared with that in the middle of Guizhou Province are shorter rainy season, less rainfall, more nonuniform precipitation and lower temperature, which resulted in a higher stable carbon and oxygen isotopic value of soil carbonate (δ13CSC and δ18OSC) and higher positive correlation coefficients of them in the west in carbonate weathering profiles. However, the climate factor can't explain the difference of δ13CSC and δ18OSC between silicate weathering profiles, demonstrate that the δ13CSC and δ18OSC are possiblely affected by other factors including the rock and vegetation type. This paper also find a negative correlation between δ13CSC and CIA (chemical index of alteration), which is related to the formation process of pedogenic carbonate. It demonstrates that δ13CSC can be an index that indicates weathering intensity, but it's also affected by other factors besides weathering. The radioactive carbon isotopes of the soil organic matter show that the average residence time of organic matter increase with soil depth, and the CO2 flux produced by decomposition of soil organic matter is higher in the upper layer |
| Subject Area | 环境地球化学 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/352002/5924 |
| Collection | 研究生_研究生_学位论文 |
| Recommended Citation GB/T 7714 | 李道静. 贵州碳酸盐岩风化壳剖面元素和同位素特征及碳汇效应[D]. 北京. 中国科学院研究生院,2014. |
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