Near-natural Assessment And Conrtol System Of Stream Ecosystems Based On The Fuzzy Matrix Assessment

River is the essential natural ecological environment for people’s living. Meanwhile, various kinds of ecology function has been developed and utilized. However, with the development of human society and economic progress, river ecosystem are suffering damages in different degrees; near-natural state of river is gradually degrading and even ecological service function of river is in an annual downward trend. Therefore, overall near-natural assessment of river, which is helpful for its recovery, and proper development and utilization of river have become one of today’s problems that have to be settled urgently.Aiming at the phenomenon that the assessment of near-natural state of river in the suburb of Beijing has no unified standard, this paper analyze the content, application range and disadvantages of existing methods of near-natural assessment of river at home and abroad, combined with the actual condition of Bai river in Huairou district in Beijing. In this place, fuzzy matrix assessment has been established to assess the near-natural state of river. This evaluation system consists of three evaluation indicators -- target layer, criterion layer and index layer. According to the corresponding relation between evaluation indicator and river, analytic hierarchy process was used to determine the weight of each indicator. Moreover, mathematical techniques were used to establish the model of near-natural assessment of river in the foundation of fuzzy matrix assessment. The model was utilized to evaluate the near-natural state of Bai river in Huairou district in Beijing, and three evaluations were made as follows. Firstly, the descending order of importance of criterion layer relative to target layer are from hydrological characteristics to geomorphic characteristics, and finally, ecological characteristics, while the weight of hydrological characteristics achieves 0.535699. It means that hydrological characteristics is the most important factor that affects the near-natural state of river. Secondly, the descending order of importance of index layer relative to target layer were arranged as follows-clear degree, slope structure, dissolved oxygen, phosphate, slope gradient, velocity diversity, slope vegetation, water conservancy measures, depth of water, current velocity, pH value, surrounding land use types, cross section morphology, width of buffer zones, the structure integrity, smell, ammonia nitrogen and width of river. Among these factors, the weight of clear degree achieves 0.340535, which means the most important condition that help river meet the near-natural state is to keep river clear. Finally, both the quantitative evaluation and qualitative evaluation of geomorphic characteristics of Bai river are the degradation of the natural state; the quantitative evaluation of hydrological characteristics is the degradation of the natural state while the qualitative evaluation of this characteristics is near-natural state; the quantitative evaluation of ecological characteristics is natural state while the qualitative evaluation of this characteristics is near-natural state. These evaluations implied that the index of near-natural state of Bai river was 2.41. According to the principle of maximum degree of membership, the overall assessment of Bai river turned out to be "near-natural state".Research findings of this paper point out the vulnerable part of near-natural state of Bai river. As Bai river in Huairou district as an example, this paper put forwards corrective actions and corresponding suggestions for restoring Bai river to ensure the health of river and sustainable development of ecological environment construction.