内陆干旱区水分驱动的生态演变机理

Water-driven ecological evolution mechanism in inland arid region

我国内陆河流域约占国土面积 1/3,降水集中在山区 ,盆地干旱少雨 ,形成内陆河平原独特的非地带性生态群落。针对内陆河干旱区水资源条件与生态特点 ,从水分 -生态相互作用机理入手 ,系统研究了以绿洲为中心的内陆干旱区沿河平原生态问题 ,以此作为干旱区生态需水研究的基础。由于径流运动的作用 ,平原生态系统表现出有序的层次结构 :以河流为中心向两岸依次为绿洲、过渡带、荒漠 ;植被等级和盖度逐渐由高向低演变 ,分别为有林地、灌木林、疏林地和高盖度草地、中盖度草地、低盖度草地、沙漠、戈壁。植被生态系统的这种规律性反映了地下径流 (潜流场 )的变化。在干旱少雨 (年降雨量小于 10 0 mm)的环境中 ,来自河川补给的潜水蒸发 ,成为植被水分最主要来源 ,对植被生态系统起决定性的作用。根据生态景观的需水补给条件界定内陆河盆地生态系统的组成 ,给出了平原生态圈层结构的定义。当水资源开发利用方式和土地利用方式发生变化时 ,水资源分布和补给条件相应发生变化 ,并导致生态系统圈层结构随之发生变化。生态圈层结构理论成为干旱区生态需水计算的理论依据和方法基础 ,据此构造定量化的水分驱动生态演变模型。利用 2 0世纪 70年代和 90年代遥感影像 1∶ 10万解译图 ,结合地面观测资料 。

In the inland river basin, the area of which is about 1/3 of China, the precipitation mainly concentrates in the mountain area but it is arid and rainless in basins. Then the special azonal ecosystem has been formed. In the inland river basin, according to the water resources condition and ecological characteristic point, starting with the interaction mechanism of between water and ecosystem, this paper systemically researched the plain ecological problems along the narrow belt of riverbank as the center of oasis, and regarded this as the foundation of researching the ecological water demand. Because of the runoff movement action, the plain ecosystem configuration is presented in a sequential hierarchy. From the river bank to the outside area are distributed as oasis, transition zone, and desert. The plant ecosystem and vegetation cover rate change as forest, shrub, sparse shrub, high cover rate grassland, low cover rate grassland, sand desert and Gobi. The arrangement rule of the vegetation ecosystem reflects the change of groundwater runoff. In the arid and rainless environment (yearly precipitation less than 100mm), the groundwater evaporation from river runoff supply is vitally useful for vegetation ecosystem, for it is the main source of vegetation water demand. The inland river basin ecosystem configuration, namely the definition of plain ecological ring and layer structure, is plotted out according to the water demand and supply conditions of the local ecological landscape. When the mode of water and land resources development and utilization was changed, correspondingly the distribution and nourishment condition of water resources was also altered, and further resulted in the change of the ecological structure of ring and layer. The ecological structure of ring and layer was regarded as the foundation of theory and method about calculating the ecological water demand in arid region, hereby the quantitative water-driven ecological evolution model was formed. By satellite image analysis with a scale of 1∶100000 from 1970's to 1990's combined with some field observation, the northwest inland region ecological and environmental situation analysis from 1970 to 1990 was carried out. The result shows that it completely coincides with the ecological structure of ring and layer theory. The general trends of the ecological zone pattern: the artificial oasis has been expanded widespread and the natural oasis shrunk; the interlaced transition zone between the desert and the oasis has been in serious degradation; the desert area has gradually increased.