| 题名 | 三峡库区消落带干湿交替作用对土壤磁性的影响 |
| 作者 | 朱宏伟 |
| 学位类别 | 博士 |
| 答辩日期 | 2012-05-21 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 贺秀斌 |
| 关键词 | 三峡库区 消落带 干湿交替作用 土壤磁性 磁性矿物 |
| 其他题名 | Soil Magnetism Changing with Alternation of Wet-dry Process at the Riparian Zone in the Three-gorge Reservoir |
| 学位专业 | 自然地理学 |
| 中文摘要 | 三峡水库消落带是目前世界上面积最广、水位涨落幅度最大、人类活动影响最为频繁与强烈的消落带，且水位涨落呈反季节枯洪规律。目前针对消落带土壤特性变化等方面研究较少。土壤磁学作为一门较新的多学科交叉应用科学，在近些年的环境学和土壤学中应用的越来越广泛。土壤磁性能够综合反映土壤矿物、容重、含水量、质地、结构等物理性质和pH值、有机质含量等化学性质。近年来，土壤磁性在考古、全球环境变化、古气候演变等研究领域广泛应用，成为表征土壤发育、生物气候的替代性指标。本研究选择3个典型的紫色土消落带监测断面，通过现场和实验室土壤磁性与其他土壤特性的测试分析，揭示三峡水库水位变化与干湿交替作用引起的土壤磁性变化规律。本文主要结论如下： （1）从三峡库区消落带内所有监测断面的土壤磁性分布结果来看，其整体上呈现随淹没水深的增加而增高的特征。如共和村附近消落带表土质量磁化率最高值与最低值相差5倍以上。其它磁性指标如IRM、SIRM、ARM、(BO)CR和χ-T曲线等，从不同角度反映出消落带中低水位土壤相对中高水位有磁性强度增强、磁性矿物晶粒减小、强磁性矿物增多等趋势。 （2）消落带土壤磁性以质量磁化率（χ）值为代表，随受干湿交替的频次增加而增高。库区在夏季低水位和冬季高水位时，都会在各自位置频繁涨落，从而使得消落带上部和下部受到干湿交替的反复作用。而对中部土壤影响频率有限且时间较短，从而会造成上下两部分土壤磁性的增强。又因为目前是三峡蓄水初期，2010年才正式达到175米高程，从年限上讲消落带上部土壤接受干湿交替作用小于下部，从而其磁性增强效果还远不及下部明显。另外，消落带内表土容重也随着海拔降低而小幅度增大。 （3）干湿交替作用不仅导致土壤理化性质变化，还导致了土壤矿物组成发生显著的变化。由消落带表土所得的频率磁化率（χfd%）与低频质量磁化率（χlf）相关关系分布规律可得消落带不同水位土壤的主要磁性矿物发生了变化。磁化率较强的分布于消落带下部，其磁性矿物组成与中上部产生了明显的区别。经χ-T曲线等磁性参数表明，消落带下部土壤中含有了中上部不存在的新的磁性矿物纤铁矿和磁铁矿。前者常温下一般不具备强磁性，况且三峡大坝蓄时间短，江水作用的时间有限，氧化还原作用的影响暂时不是主要因素。据(BO)CR、扫描电镜(SEM) 等磁性参数等实验证实，消落带下部土壤存在浑圆状的磁铁矿，海拔越低越容易找到。推测其来自上游重工业企业等，在频繁的干湿交替的过程中吸附和沉积在了土壤颗粒上。 |
| 英文摘要 | The riparian zone in the Three-gorge Reservoir is the area that the vastest, the biggest water level fluctuation amplitude, and the most frequent human activities, all over the world. And it is characterized by water level fluctuation against the season of rainy or dry. They have been changed dramatically that the terrestrial ecological environment, terrestrial ecosystems, especially biomes and soil characteristics, when the early stages of the fluctuating zone formation. Currently, the study about vegetation restoration and soil erosion are numerous, however, the field of soil characteristics changing is fewer. Soil magnetism, as a new multi-disciplinary cross-applied science, is applied in environmental science and soil science more and more widely in recent years. Soil magnetism can reflect physical properties such as soil mineral species, bulk density, moisture content, texture, structure, and chemical properties such as pH value, organic matter content and so on. As there are lots of advantages and features about the soil magnetic measuring including high sensitivity, high resolution, good repeatability, low cost, simple, rapid, and it just need very small amount of sample with non-destructive, it is used in research fields of archeology, global environmental change, and paleoclimate evolution widely in recent years. It has also become an alternative characterization of soil development, bio-climatic indicators. In this study, three typical purple soil monitoring sections are selected in riparian zone. Soil magnetic variation and influencing factors are discovered caused by wet and dry alternating after water level changes in the Three Gorges reservoir, through field measuring, laboratory experiment, more importantly, the analysis of soil magnetic and other soil characteristics test. The main conclusions are as follows: (1) From the soil magnetic distribution results of all monitoring sections in riparian zone of the Three Gorges Reservoir, it shows that soil magnetic increased with the augment of the submergence. Topsoil magnetic susceptibility (χ) values in riparian zone near Gonghe village are about 20 to 30 (10-8m3/kg) at higher elevation (169 to 175 m), similar to local background values. It begins to slowly decline to 15 to 20 (10-8m3/kg) or so near the middle (169 to 157 m). While the lower elevations, especially below 157 m, it climbs gradually to 100 (10-8m3/kg) or more. The overall rise range is more than five times. Other magnetic parameters such as the IRM, SIRM, ARM, (BO)CR and χ-T curve also can reflect the trend of magnetic intensity, grain size decreases, and the strong magnetic minerals increased at lower water levels from different angles. (2) Soil magnetism, such as magnetic susceptibility (χ), is the higher value the more frequent of the wet and dry alternating in riparian zone. Water level is always uninterrupted fluctuations in their respective location, regardless to maintain the low water level in the summer or to maintain a high level in the winter at the Three Gorges reservoir area. Thus the top and the bottom of the soil in the zone will have more chance of repeated wet and dry alternately. Whereas the frequent effect is limited and its time is short for the soil at middle part. The soil magnetic enhancement is more obvious at the upper and lower part. Furthermore it is still at the beginning process of the Three Gorges reservoir, the water storage time is not a long time, not up to 175 meters high until 2010. From the process duration of speaking, the intensity of wet and dry alternation on the soil of upper part is much less than the lower. So its magnetic enhancement is also far less than the lower part. Besides, soil magnetism shows a certain extent downward trend, at the middle of the zone. This makes the soil magnetic showing “both ends higher, and middle lower”. That is significantly positive correlation with clay, silt volume fraction distribution in the topsoil. It can be judged that is caused by the river, after contrasting with the soil magnetic background. Because the fine-grained soil has relatively stronger magnetism locally, it shows that the fine-grained part, maybe due to poor erosion resistance, has been moving to the lower for the role of the fluctuating water. In addition, the topsoil bulk weight has a little increase with the altitude decrease. (3) Alternating wet and dry role is not only making soil physical and chemical properties changing, also led to changes of mineral composition significantly in riparian zone soil. The main magnetic minerals in the soil at different water level are changed attributed to the distribution and the relationship between frequency dependent susceptibility (χfd%) and low-frequency magnetic susceptibility (χlf) at the topsoil. The stronger magnetic susceptibility soil is located at the lower riparian zone，where the magnetic mineral composition is obvious differences with the upper. By the χ-T curve and other magnetic parameters shows that, there are new magnetic minerals in the topsoil at lower level, lepidocrocite and magnetite, which are not exist at the higher. The lepidocrocite is generated in soil during the period of the alternation of redox environment by fluctuating, and the traces have been found by field survey. But it do not have strong magnetic generally at room temperature, so it is not the main reason to enhance soil magnetic properties. Moreover, the Three Gorges Dam has built several years before, the role of river is limited, and oxidation reduction is not a major factor temporarily. According to the experiments of (BO)CR, scanning electron microscopy (SEM) and other magnetic parameters, it is confirmed that there are rounded magnetite at the lower part, and the lower the altitude the more easy to find. They could not find in the upper part. It can be speculated that the rounded magnetite generated by burning fossil fuels from heavy industry upstream. They are carried to downstream along the river, then adsorbed and left to the soil particles in the process of frequent alternating wet and dry. It is the major input source of the foreign magnetic substances. |
| 语种 | 中文 |
| 公开日期 | 2013-01-16 |
| 内容类型 | 学位论文 |
| 源URL | [http://192.168.143.20:8080/handle/131551/4816]  |
| 专题 | 成都山地灾害与环境研究所_山地表生过程与生态调控重点实验室 |
| 推荐引用方式 GB/T 7714 | 朱宏伟. 三峡库区消落带干湿交替作用对土壤磁性的影响[D]. 北京. 中国科学院研究生院. 2012. |
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