A Study On Spatial-temporal Distribution And Geological Factors Of Eco-environmental Vulnerability In The Middle-lower Reaches Of The Dadu River Watershed,China

Ecological environment is the premise and foundation of human survival and development.Under the dual pressure of the climate change and the intensified human activities,the world was suffered increasingly serious resource and environmental problems,such as the biodiversity reduction,land desertification,forest vegetation destruction and water resources crisis,which pose a major challenge to sustainable development.China is one of the countries with the largest distributed area,the most fragile ecological types and the most obvious manifestation of ecological fragility in the world.At present,the research on eco-environmental vulnerability has become a hot issue in the field of sustainable development.Studying on ecological environment vulnerability and its geological influencing factors can understand the ecological environment more thoroughly and comprehensively from the perspective of earth system science research,so as to scientifically cope with the risks brought by global environmental changes and promote the harmonious development of human-land relations.The Dadu River Watershed is located at the transition zone from the southeast margin of the Qinghai-Tibet Plateau to the mountain area in western margin of Sichuan Basin.It is an important water conservation area in the upper reaches of Yangtze River and Yellow River and Chengdu Plain.The River spans two first-class tectonic units,with the upper reaches located in the Songpan-Ganzi orogenic belt and the middle and lower reaches are located at the Yangtze Block.The Dadu River Watershed belongs to the southwest mountain area of China's five ecologically fragile areas,with complex geology and geomorphology,diverse climate types and frequent geological disasters.It is a sensitive zone of climate and biological response and a natural experimental area for the study of vulnerability distribution and controlling its distribution factors.Scientific cognition of temporal and spatial distribution characteristics and influencing factors of ecological environment vulnerability in Dadu River Watershed is of great significance for ecological barrier protection and poverty alleviation development in western Sichuan.At present,the previous literature research are fouces on the river morphology,geological structure,geological disasters,climate change of the Dadu River Watershed,but the ecological environment vulnerability research of Dadu River is less,and the relationship between eco-environmental vulnerability and geological factors is lacking.This study takes the middle and lower reaches of Dadu River as the study area.the concepts and connotations of ecological environment,geological environment and ecological environment vulnerability are further elaborated for the first time.It uses the theories and methods of geology,geography,ecology,mathematics and other disciplines to establish the evaluation index system,construct the evaluation model,carry out the evaluation and analyze the spatial and temporal process of eco-environmental vulnerability in the study area.On this basis,aiming at the main geological factors in the geological environment of the study area,the association rules between ecological environment vulnerability and geological factors are constructed,and the main geological factors affecting the ecological environment vulnerability of the study area are explored by qualitative and quantitative methods.This study also provides decision-making basis for ecological environment protection and construction in Dadu River Watershed.The main results of this thesis are as follows: According to the actual situation of ecological environment in the study area,referring to the existing index system of ecological environment vulnerability,the evaluation index system of the study area is established by selecting 9 factors,such as elevation,slope,vegetation coverage,soil erodibility K value and economy.The projection pursuit model and GIS technology were introduced to evaluate the eco-environmental vulnerability in 2000 and 2015,and five divisions were obtained,including severe vulnerability,moderate vulnerability,slight vulnerability,slight vulnerability and potential vulnerability.Based on the principles of importance,correspondence and feasibility,starting from two aspects of geological formation and structure,lithology and fault are selected.And five dimensions of rock type,rock hardness,fault density,distance from fault and fault strike are established,and 26 geological factors are screened out by using relevant standards and natural breakpoint method.Rough set model is introduced as the relationship model between ecological environment vulnerability and geological influencing factors,and the correlation between vulnerability grade zoning and geological factors is studied.The results show that the fragility of ecological environment in the study area is mainly related to rock type,rock hardness,fault density(m/km2),distance from faults(m)and fault strike.It is found that the influence degree of these geological factors on the vulnerability of ecological environment in the study area is ranked as follows: rock type> rock hardness > fault density > distance from faults > fault strike.