青藏高原开发中的冻土问题

THE PROBLEMS ASSOCIATED WITH PERMAFROST IN THE DEVELOPMENT OF THE QINGHAI-XIZANG PLATEAU

在国家决策西部大开发战略之际，正确评价青藏高原开发中所面临的冻土问题，为生态环境建设和国民经济持续稳定发展提供依据，显得更为重要。多年冻土占据着青藏高原一半以上的疆土面积，受全球气候变化和人为活动的共同影响，在过去的几十年中已发生了不同程度的变化，且随着人类活动增强，变化必将加剧，冻土问题也将显得日益突出。多年冻土的变化主要表现为多年冻土的地温升高、上限下降和面积缩减等，进而影响到各类工程的地基稳定性，使工程建筑受到不同程度的破坏；同时，由于气候变化、过度放牧和工程活动的影响，地面水热状况改变，尤其是地表土壤层中水分含量的降低，导致了草场退化，生态环境恶化。在分析这些冻土问题原因的基础上，作者预测了在未来开发中可能出现的冻土问题，并提出了建议。

About 54.3% area of the Qinghai-Xizang Plateau is underlain by permafrost. It is the largest in area and highest in elevation in the low and middle latitude regions. Since Pleistocene, the plateau permafrost experienced a series of changes following the alternate changes of glacial and interglacial periods. Especially during the past two decades, the degradation of plateau permafrost is becoming more obvious. The permafrost degradation will continue under the global warming trend. In order to set the strategy for the development of the western China, it is imperative to assess the problems associated with permafrost in the Qinghai0izang Plateau, to study the impact of anthropogenic activities on permafrost in lieu of climatic and environmental changes, and to predict possible changes in permafrost environment to meet the requirement of sustainable development of the Qinghai-Xizang Plateau. The major problems in the development of the Plateau are engineering geology and environment protection. The problems about engineering geology are mainly frost expansion caused by water movement and freezing in permafrost, and subsidence caused by thermal karst and deformation. These are the causes of all engineering geology problems in permafrost zone. The destructions of all kinds of structures in the permafrost zone are caused by frost heave and poor geological conditions. The ecosystems of the Qinghai-Xizang Plateau are very fragile and closely related with the permafrost dynamics. The vegetation communities of the permafrost zone in the Plateau gradually changed from temperate communities to younger ones adaptable to cold and arid environment following the rising of the Plateau. Because of the long period of adaptation to the Plateau environment, many plants developed a series of morphology cology characteristics to adapt the alpine environment. The internal structure exhibits many characteristics. Permafrost limits the moisture exchange between ground surface and the upper permafrost. This is the primary factor controlling the moisture regimes of the plant communities and wetland distribution in both time and space. The drastic and extensive periglacial process also produced different ecological effects. Since the 70′s, the plants colonial superiority increased and the biodiversity also increased following the degradation of permafrost. The combined effects enhanced desertification. The permafrost of the Qinghai-Xizang Plateau is very sensitive to changes in climateand ground surface conditions. Changes in permafrost directly affects hydrological processes. Permafrost is a special thick regional aquater. It separates the same aquatar into super ections and sub ections. It retards the direct hydrological interaction between the two sections and formed two totally different aquafers. The ground water of the Qinghai-Xizang Plateau can be divided into three basic types: aquafer above permafrost, aquafer below permafrost and talik. Water sequestration and release during seasonal freeze and thaw adjust the soil water, subsurface and even ground water flow, which vary obviously with seasons. During the development of the western China, the first priority is to protect the water resources. Over ithdraw of water resource will unavoidably cause a series of environmental and engineering problems in water resources and peripherial regions. Currently, there are two major kinds of human activities in the permafrost zones on the Plateau; livestock and engineering activities. On the premise of global change, human activities have already caused permafrost and environment changes. Scientifically designed model for sustainable livestock development and associated management practices are the key to optimum livestock development. There are increased various human activities including tourism, thus it is important to establish scientific and economic design and construction for different permafrost regions to ensure the normal function of different projects. Meanwhile, it is essential to ensure the minimization of destruction and