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黄土丘陵区小流域侵蚀产沙对坡耕地退耕响应的137Cs法研究
Alternative TitleA Study on Responses of Soil Erosion and Sediment Yield to Closing Cultivation on Sloping Land in a Small Catchment Using 137Cs Technique in the Rolling Loess Plateau, China
Language中文
冯明义
Thesis Advisor张信宝
2003
Degree Grantor中国科学院成都山地灾害与环境研究所
Place of Conferral成都
Degree Name博士
Degree Discipline自然地理学
Keyword137cs含量 输沙模数 相对来沙量 小流域 黄土丘陵区
Abstract土壤侵蚀是全球普遍的环境问题。黄土丘陵区是中国水土流失最严重的地区之一,查明不同类型土地土壤侵蚀速率和相对来沙量,对于正确评价小流域坡耕地退耕的侵蚀泥沙响应和退耕还林(草)的水土保持效益具有重要意义。传统的侵蚀研究方法需要大量资金和长期观测,都存在一定的局限性。137Cs是土壤侵蚀研究的一种良好示踪源,在土壤侵蚀研究中137Cs法已经取得了丰硕成果,但通过坝库沉积泥沙137Cs含量的变化分析土地利用变化的侵蚀产沙响应的研究极少。论文在系统分析国内外侵蚀泥沙137Cs示踪研究进展的基础上,详细介绍了137Cs示踪技术的基本原理、样品采集、处理和测试方法。论文以黄土丘陵区赵家沟小流域为例,运用坝库沉积泥沙和137cs示踪技术分析了退耕引起的相对来沙量的变化。通过赵家沟的研究,揭示了黄土丘陵区坡耕地大规模退耕的侵蚀产沙响应。主要研究结论如下:1.1994-1996年期间,赵家沟年平均降水量528.4mm,接近多年平均降水量512.8mm,但3年的年均输沙模数29,650tkm-2yr-1,为多年平均输沙模数13,413tkm2yr-1的2.2倍,表明黄土丘陵区退耕不禁牧,小流域输沙模数不仅没有减少,反而有所增加。2.坝库沉积泥沙的137cs含量,从1994年的0.75 Bq kg-1,急剧减少到1995年的0.49Bq kg-1,1996年的0.18Bq kg-1。沟间地相对产沙量从1994年的23%减少到1995年的15%,1996年的6%;沟谷地相对产沙量从1994年的77%增加到1995年的85%,1996年的94%。3.梁如坡地退耕后,沟间地侵蚀明显减弱,输沙模数从1994年的14,335 tkm-2yr-1减少到1995年的7,037 tkm-2yr-1,1996年的3517 tkm-2,yr-1;沟谷地侵蚀明显加剧,输沙模数介于44,944 t km-2yr-1和62,136 tkm-2yr-1之间,远高于1993年前的21,118t km-2yr-1。4.梁筛坡地区退耕后,沟间地侵蚀减弱,沟谷地侵蚀加剧的主要原因可能是:退耕后耕作土逐渐密实,抗蚀性增强,侵蚀减弱,但土壤密实后入渗速率降低,梁饰坡地产流量增加,梁如坡地流入沟谷的径流加大,加剧了沟谷地的冲沟侵蚀和重力侵蚀,沟谷地的侵蚀量和相对产沙量增大,从而导致流域输沙量增加。5.黄土_.陵区梁饰坡地大面积退耕对于控制该地区严重的水土流失,长期(而不是短期)是有益的,因为黄土地貌是一种刘径流变化极为敏感的地貌类型,小流域的产汇流变化势必要影响到地貌的演化,地貌形态调整到适应退耕后的土地利用格局和水文态势,需要有一个过程。这一过程的初期沟谷侵蚀的加剧是不可避免的,但随着梁如坡地和沟谷内植被的恢复,沟谷侵蚀将逐渐减弱,流域输沙量也将随之减少。
Other AbstractSoil erosion has become a worldwide environmental problem. The Rolling Loess Plateau is one of the most severe areas with soil erosion in China. To evaluate the effectiveness of soil conservation countermeasuresi it is very important to investigate soil erosion rate and relative contribution of sediment yield derived both from the gully area and inter-gully area. Traditional methods present many limitations in cost and time for observation and monitoring. Cs, is now widely applied in soil erosion researches, for it is easy, cheap and effective. But few publications can be consulted about sediment sources changes in the same catchment by comparing the change of relative contributions of sediment yield from different sources. Based on progress analysis of 137Cs techniques, this thesis comprehensively introduced the basic principles of this field as well as methodology involving sampling, pre-treating and measuring. Taking a small catchment, Zhaojia Gully catchment, on the Loess Plateau of China as a sample, relative sediment sources changes resulted from closing cultivation was analyzed by using reservoir deposits and 137Cs technique.The main conclusions are as follows: 1. The mean annual precipitation was 528.4 mm during the period of 1994-1996, which was close to the average value of 512.8 mm for a long term since 1950s. However, the mean specific sediment yield of 29, 650 t km-2 yr-1 during the period of 1994-1996 was 2.2 times of the long-term average specific sediment yield of 13,413 t km-2 yr-1 in the Zhaojia Gully catchment. It indicated that closing cultivation without prohibition of heavy grazing could not reduce sediment yield but increase it. 2. I37Cs content of the deposited sediments in the reservoir in the catchment sharply declined from 0.75 m Bqg-1 in 1994 to 0.49 m Bqg-1 in 1995, and 0.18 m Bqg-1 in 1996. Relative contributions of the sediment derived from the rolling plateau area to the total sediment yield in the catchment decreased from 23 per cent in 1994 to 15 per cent in 1995 and 6 per cent in 1996, while the relative sediment contribution from the gully area increased from 77 per cent in 1994 to 85 per cent in 1995 and 94 per cent in 1996. Due to closing cultivation on sloping land, soil erosion in the inter-gully area has been clearly reduced, and the specific sediment yields of the area dropped from 14, 335 t km-2 yr-1 in 1994 to 7,034 t km-2 yr-1 in 1995 and 3,517 t km-2 yr-1 inl996. But, erosion in the gully area has become severe, and the specific sediment yield of the area varied between 44,944 t km'2 yr"1 and 62, 136 t km-2 yr-1, which was much greater than the value of 21,118 t km-2 yr-1 before 1993. It is suggested that compacting of ploughed soils increased erosion resistance but decreased precipitation infiltration rate, therefore, the soil erosion was reduced but the runoff amount increased on the inter-gully area. Increase of delivering runoff from the inter-gully area to the gully area should result in activeness of gully erosion and mass movements, consequently, increased the sediment yield and relative sediment contribution of the gully area as well as the total sediment yield of the catchment. Closing cultivation on vast rolling plateau surface area is beneficial for control of the severe soil erosion in the Rolling Loess Plateau in a long term, but not in a short term. It is because that the loose loess soil is susceptive to water erosion, therefore, the loess plateau landform is susceptive to hydrological condition changes. It may be a long way to go for the landform adjusting to the hydrological condition changes after closing cultivation in the Loess Plateau. Therefore, an increased gully erosion immediately after closing cultivation can not be avoided. But the gully erosion will be reduced and the specific sediment of the catchment will be decreased after the vegetation rehabilitated both on slope and in the gully area.
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/7796
Collection成都山地所知识仓储(2009年以前)
Recommended Citation
GB/T 7714
冯明义. 黄土丘陵区小流域侵蚀产沙对坡耕地退耕响应的137Cs法研究[D]. 成都. 中国科学院成都山地灾害与环境研究所,2003.
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