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土壤侵蚀被认为是喀斯特地区土壤退化的主要形式，其作为一种自然地貌的形成过程是可以被人为活动影响的，主要通过森林砍伐、过度放牧和粗放的农业活动等行为加剧这种过程。同时，各种地貌形成的过程也依赖于化学风化作用；化学风化作用将基岩转化为可侵蚀的风化层，从而加速地表的演化。由于中国西南喀斯特地区土壤侵蚀状况严重，岩石风化提供的矿物养分在不同土壤侵蚀状况及不同地貌条件下的迁移特征一直是值得研究的重点。本文采集了重庆南川区、广西南丹县和桂林市三处坡地不同部位的土壤剖面为研究对象，运用地球化学与137Cs核素技术方法分析了元素地球化学行为、坡地土壤侵蚀特征等，得出以下认识：南川坡地在山顶森林覆盖土壤发生土壤沉积现象（侵蚀模数为-11.88 t ha-1 yr-1），山腰和山脚处侵蚀模数大于微度侵蚀规定的500 t ha-1 yr-1，属于轻度侵蚀。该研究进一步表明，人类活动的影响，如道路建设、采矿和森林砍伐，可以显著加快土壤侵蚀速度。常量和微量元素数据表明，该坡地土壤是下覆基岩的原位风化产物。山顶沉积剖面土壤元素损失以化学侵蚀为主。山腰发生显著侵蚀，且经历了强烈的化学风化作用，从而得出在一定的土壤侵蚀速率下，没有新鲜土壤物质输入的剖面会经历最强的化学风化作用，导致易风化矿物（如长石）的大量溶解。广西南丹坡地在山腰林带位置发生土壤沉积现象，然而坡地平均侵蚀模数为轻度侵蚀。山腰林带沉积现象和山顶及山脚土壤侵蚀的鲜明对比，仍然强调了植被覆盖对土壤保持的重要性。元素数据显示三个剖面土壤来自同一种物源，且坡地山腰和山脚剖面有着山顶剖面侵蚀物质的继承性。不活化元素在山腰剖面（沉积剖面）富集、在山脚剖面亏损，这些元素主要以颗粒态的形式物理横向迁移；而溶解度较好的微量元素并不会随土壤沉积发生富集现象。广西桂林硅酸盐岩坡地山顶和山腰剖面的土壤侵蚀模数分别为-22.28和36.71 t ha-1 yr-1，山腰处属于中度侵蚀。山腰剖面近期遭受严重的人为扰动是导致该位置遭受严重土壤侵蚀的原因。与山顶沉积剖面土壤样品相比，山腰侵蚀剖面中的所有常量与微量元素均亏损，含量明显减少。与山顶沉积剖面相比，山腰侵蚀剖面所有稀土元素均发生亏损现象，这个现象也暗示着化学侵蚀（溶质态）的稀土元素并不易富集于某处。对不同植被覆盖土地137Cs浓度来说，得出林地>草地>荒地>人为扰动土地。土壤侵蚀模数与影响因子的相关性分析表明植被覆盖与侵蚀模数呈显著正相关（R2 = 0.70），此结果进一步明确了加大植被覆盖和减少人为干扰对喀斯特地区水土保持的重要性。坡度也是影响坡地土壤侵蚀的另一个关键因素，坡地越小，侵蚀状况越小。本文还测得南丹地区2014年137Cs面积比活度本底值为883.86 Bq m-2，通过对比其他学者2006年与2009年该地区周边的137Cs本底值得出该本底值合理可靠。该值将为桂西北地区137Cs示踪法的应用提供可靠时效的数据支持。植被覆盖有效减少土壤侵蚀，但对元素化学侵蚀起到了促进作用，在南川和南丹坡地上植被覆盖最好的剖面处土壤元素均显亏损，其中南丹坡地山腰林带土壤常量元素富集系数达到-0.6。土壤元素迁移行为表明物理侵蚀和化学侵蚀间存在着拮抗作用，两者此消彼长。然而桂林坡地山腰处土壤元素却亏损严重，由此得出人为扰动会打破这种平衡，加剧二种侵蚀过程的进行。

Erosion, as one of the major forms of human induce soil degradation in karst areas, are natural landscape-forming processes, which can be accelerated by human activities through deforestation, overgrazing and poor farming practices in different geomorphological hillslope components. At the same time, the process of geomorphic formation also depends on chemical weathering. Chemical weathering transforms bedrock into erodible weathering layers, thus accelerating surface evolution. Due to the serious soil erosion in the karst region of southwest China, the migration characteristics of mineral nutrients provided by rock weathering under different soil erosion conditions and different geomorphological conditions have always been the focus of research. In this study, we investigated the spatial characteristics of soil erosion modulus, the mechanism of soil element behaviors in three typical karst hillslopes in Nandan County of Guangxi Province, Nanchuan District of Chongqing City and Guilin City of Guangxi Province.The soil deposition phenomenon (erosion modulus -11.88 t ha-1 yr-1) occurred in the forest profile of Nanchuan hillslope located at the sumimit position (erosion modulus -11.88 t ha-1 yr-1), and the erosion modulus at the shoulder and toeslope profile were larger than 500 t ha-1 yr-1 that defined as mild erosion. The study further suggests that the effects of human activities, such as road construction, mining and deforestation, can significantly accelerate the rate of soil erosion, particularly at the toeslope of hillslopes with sparse vegetation cover. The data of major and trace elements indicate that the soil in this hillslope is the in-situ weathering product of underlying bedrock. The loss of soil elements in the summit deposition profile is dominated by chemical erosion. Significant erosion occurred on the shoulder prifile, which experienced strong chemical weathering. It was concluded that at a certain soil erosion rate, the profile without fresh soil material input would experience the strongest chemical weathering, leading to massive dissolution of easily weathered minerals (such as feldspar).Soil deposition occurred on shoulder forest belt of the Nandan hillslope, but the average erosion modulus of the hillslope was belong to slight erosion. The contrast between shoulder forest soil deposition and soil erosion at the summit and toeslope of the hillslope still highlights the importance of vegetation cover for soil conservation. Element data showed that the three profile soil draw from the same source, and the shoulder and toeslope profile had the inheritance of the eroded material in the summit profile. The inactive elements were enriched in the shoulder profile (sedimentary profile) and lost in the toeslope profile. The trace elements with better solubility will not be enriched with soil deposition.The soil erosion modulus of the summit and shoulder profile of Guilin silicate hillslope were -22.28 and 36.71 t ha-1 yr-1 respectively, and the shoulder profile is belong to moderately eroded. The recent severe anthropogenic disturbance in the shoulder profile is the main reason for the severe soil erosion in this position. Compared with the soil samples in the summit deposition profile, all the major and trace elements in the shoulder erosion profile were deficient. The loss of all rare earth elements in the shoulder erosion profile compared to the summit deposition profile also suggests that the rare earth elements migration via chemically eroded (solute) are not readily concentrated in one place.For the concentration of 137Cs in different vegetation covered lands, it can be concluded that woodland>grassland>wasteland>human disturbed lands. The correlation analysis of soil erosion modulus and impact factor shows that there is a significant positive correlation between vegetation coverage and erosion modulus (R2 = 0.70), which further confirms the importance of increasing vegetation cover and reducing human disturbance for soil and water conservation in karst areas. Slope is another key factor affecting soil erosion on hillslope. This study also measured the reference value of 137Cs in Nandan region in 2014 as 883.86 Bq m-2, which is reasonable and reliable by comparing the other scholars’ 137Cs reference values around the region measured in 2006 and 2009. This value will provide reliable and timely data support for the application of 137Cs tracer method in Northwest Guangxi. Vegetation coverage effectively reduced soil erosion, but promoted element chemical erosion. Soil elements were significantly reduced in the profiles with the best vegetation coverage on the hillslope of Nanchuan and Nandan, and the enrichment factors of soil major elements in the hillside forest belt of Nandan hillslope reached -0.6. The magration of soil elements indicates that there is antagonism between physical erosion and chemical erosion. However, the soil elements loss in the shoulder of Guilin hillslope are seriously, so it can be concluded that human disturbance will break the balance and intensify the two erosion processes.