【作者】 李晓丽；

【导师】 张成君；

【作者基本信息】 兰州大学 ， 环境科学， 2008， 硕士

【摘要】 黄土高原西部的定西地区生态环境极其恶劣,水土流失、土地贫瘠、水资源短缺等一系列生态环境问题严重制约着人类社会和经济的可持续发展。本文通过研究定西鲁家沟黄土剖面的环境变化记录,以¹⁴C、磁化率、碳酸盐、粒度、有机质含量等手段,恢复了定西地区全新世的气候变化过程。在此基础上,结合其它历史文献资料,探讨了全新世以来人类活动的过程,指出人类的活动与气候环境的变化密切相关。主要研究结果如下:定西地区全新世以来的气候环境变化可分为以下三个阶段:（1）全新世早期（11200-7560 cal aB.P.）,气候虽然转暖转湿,但整体上较为寒冷,期间存在多次气候冷暖、干湿变化。9740-8300 cal aB.P.,地层中频率磁化率增加,有机质含量保持一个较高值,表明夏季风增强,降水量增加,表现为一层弱发育的古土壤层:早全新世期间也出现一个短暂的冷干事件,时间在8000-7560 cal aB.P.。（2）全新世中期（7560-3600 cal aB.P.）,气候较为温暖湿润,但前期降水量较少,在后期4350-3600 cal aB.P.期间为本地区降水量最多的时期。期间存在发生在4100-3900cal aB.P.的气候冷干事件。（3）全新世晚期（3600-1167 cal aB.P.）,气候向干旱化方向发展,期间在2800-2560 cal aB.P.发育古土壤层,但是成壤强度很弱,表明夏季风有短暂的增强。通过与其他地区气候变化对比,发现本区全新世的气候变化不仅具有鲜明的区域性特征,同时也具有全球一致性。但气候阶段与气候事件的起讫时间、变化幅度和持续时间有区域差异,可能是由于区域性地形和大气环流形势的差异,致使对全球气候变化的响应时间和敏感程度都不一样。全新世早期就已经有古人类开始在黄土高原西部繁衍生息,主要以狩猎等非农业生产方式生活,虽然进行了简单的农业生产,但是生产力十分低下,刀耕火种的生产方式还不足以对环境产生影响。到了全新世中期,温暖湿润的气候,为古人类的生存和发展提供了优越的自然环境,史前文化开始大规模向西扩展到祖厉河流域。6000年左右定西地区人类活动范围急剧扩大,同时对环境的影响也就增强。本区先后发展了仰韶文化、马家窑文化、齐家文化,原始农业虽然发达,但是这一时期人类的生产力水平落后,会对植被造成一定破坏,但也只是局部的,人类活动对环境的影响还非常有限。而且,由于气候适宜,环境的自我调节和抗干扰能力也比较强。全新世晚期以来,气候向干旱化方向发展。秦汉以前,定西地区植被覆盖较好,气候的干旱化发展以自然因素为主;秦汉以后,一方面由于气候条件的恶化,另一方面定西地区人口的急剧增加,生产力水平的提高,人类为了自己的生存创造更好的物质条件,人类开始不顾一切的开垦土地、滥垦滥伐滥挖、过度放牧以维持生存,再加上自古以来就盛行的广种薄收轮荒制度,致使地表植被严重破坏。正是这种大规模的人类活动,导致自然植被的破坏,地表缺乏植被的保护,造成土壤侵蚀加剧,从而导致水土流失、土地贫瘠、水资源短缺等一系列生态环境问题。定西地区生态环境的恶化,大体上始于北宋,而在明清以后则急剧恶化。由此可见,现代定西地区生态环境的恶化,是过去3600多年来,在气候条件恶化的背景下,叠加了人为恶化因素的结果,但是这种变化以人为因素居多。由此而导致的严重的水土流失和水资源的极度缺乏,是导致定西生态环境恶化和经济落后的直接原因。更多还原

【Abstract】 Dingxi area is located in the west of Loess Plateau, ecological environment is extremely bad. The soil erosion, poor soil, the water resources short and a series of ecological environment problems are restricting the human society and the economical sustainable development. Based on the records of environmental changes in Lujiagou loess section, ¹⁴C, magnetic susceptibility, carbonate, particle size, organic matter content and other means to obtain a higher resolution of the Holocene environmental changes sequence and reconstracted climatic changes process of the Holocene in Dingxi area. Meanwhile, in combination with other historical documents, we discussed the human activities process, points out humanity’s activities and changes of the climatic and environmental close related. The main findings are as follows:Climatic changes of the Holocene in Dingxi area can be divided into three stages: （l）Early the Holocene （11200-7560 cal aB.P.）, climate is becoming warm and wet, but it is cold, on the whole. But there are several times during the wet or dry and cold or warm changes.9740-8300 cal aB.P., this stratum frequency magnetic susceptibility increases, the organic content maintains a high value, indicated that the summer monsoon strengthens, the precipitation increases, there is a weak palaeosoil developmented.During the early Holocene also a short-term cold and dry event, the time is in 8000 - 7560 cal aB.P.. （2）Middle the Holocene （7560-3600 cal aB.P.）, the climate is warm and humid, but less precipitation early, in later 4350-3600 cal aB.P., maximum precipitation in this region during this period. There occurred a cold and dry weather event in 4100-3900 cal aB.P..（3）Late the Holocene （3600-1167 cal aB.P.）, the climate is becoming drying, in the period 2800 to 2560 cal aB.P., developed a palaeosoil layer, but a weak soil strength, and it indicated that the summer monsoon has a short-term summer monsoon enhancement. Contrast with the other areas of climatic changes, we found that climatic changes in this district during the Holocene not only has the distinct regional characteristics, but also has the global consistency.But the climate stages and the climate events’s beginning and ending time, the change scope and the duration have the region differences, possibly is as a result of the differences of regional terrain and the atmospheric circulation situation, causes differences of the global climate changes response time and the sensitive degree.Humans have already lived in the western of Loess Plateau in the Early Holocene, mainly hunts and non-agricultural production ways to life, although have carried on the simple agricultural production, but the productive forces is very low, the slash-and-burn cultivation production method have few influence on the environment.Middle Holocene, climate is warm and humid, and may be a superior natural environment for ancient human’s survival and development , the prehistoric culture started to expand massively to the west to the Zuli River basin.About 6000 the scope and depth of human activities in Dingxi area dramatically expanded, and simultaneously the influences also strengthened on the environment.Has developed the Yangshao culture, the Majiayao culture, the Qijia culture successively, although the primitive farming is developed, but this time humanity’s productive forces level is backward, the production of the original agriculture,to a certain extent,have influences on the vegetation, but it was only partial, the human activities does not significantly impact on the environment.Moreover, as a result of the climate optimum, the environment self-adjustment and antijamming ability is also quite strong.Since the late Holocene, climate is becoming dry, the impact of human activities also increasing. Before the Qin and Han Dynasties, Dingxi area vegetation cover is good, climate dry desiccation development by natural factor primarily.After the Qin and Han Dynasties, on the one hand as a result of climatic conditions worsening, on the other hand population of Dingxi area sharp growth, productive forces level enhanceed, humanity created the better physical conditions for their survival, they started to reclaim land, reclamation deforestation, over-grazing to maintain the survival, coupled with the prevalence of the Loess Plateau since ancient times were thin at the round-Arakawa system, which severely damaged the ecological environment. This kind of large-scale human activities,causes the natural vegetation’destruction, the surface lack the vegetation protection, causes the soil erosion to intensify, thus causes the soil erosion, the land to be barren, water resources short and a series of ecological environment problems. The deterioration of the ecological environment in Dingxi area, begins in the Northern Song Dynasty on the whole.But the massive destruction, in the Ming and Qing Dynasties.Thus it can be seen, The deterioration of the modern ecological environment in Dingxi area, has been past 3600 for many years, has superimposed the double impact of the natural process and human activities, but this kind of change by human factor majority.Serious soil erosion and the extreme lack of water resources are the main reasons for the deterioration of the ecological environment and economic backwardness in Dingxi area.更多还原