Study On The Evolution And Driving Mechanism Of Typical Wetlands In The Middle And Lower Reaches Of The Yellow River

The wetlands in the middle and lower reaches of the Yellow River are an important part of the ecosystem of the Yellow River Basin,providing a natural habitat for many rare animals,and playing an important role in conserving water sources,regulating the climate and maintaining the stability of the ecosystem.However,with the effect of many factors such as global climate change and human activities,the hydrological characteristics of the Yellow River have changed significantly,and the wetland pattern of the Yellow River has also changed.Therefore,systematically exploring the evolution of the Yellow River wetland pattern and its driving factors can provide help for revealing the development process of the Yellow River wetland,protecting the wetland resources of the Yellow River Basin,providing a certain theoretical support for wetland restoration and is of great significance for accelerating the development of ecological protection strategies in the Yellow River Basin.This paper selects the basin from Sanmenxia to Xiaolangdi as the research area.The main research contents and conclusions are as follows:(1)Based on ENVI5.3 and Arc Gis10.2 software technology platform,remote sensing interpretation was used to study the wetland area and type changes of four remote sensing images in 1989,1997,2008 and 2018,respectively.It was found that natural wetland was dominant in the study area,accounting for more than 95% of the total wetland area,and the proportion of artificial wetland was not more than 5%.Using the pixel dichotomy model and ecological evaluation model to study the wetland vegetation and ecological changes,it was found that the average vegetation coverage in 1989,1997,2008 and 2018 were 0.59,0.51,0.72 and 0.55,respectively,and the comprehensive index of ecological environment were 6.11,5.70,5.55 and 5.86,respectively.The areas with high vegetation coverage were mainly located in the northwest and northeast of the study area.The ecological environment of the area near the main and tributaries of the Yellow River is more fragile than that of other places in the reservoir area,and the ecosystem function and self recovery ability are also weak.The ecological condition of the Yellow River and its tributaries has experienced a trend of getting worse at first and then getting better.(2)M-K nonparametric test and wavelet analysis were used to study the characteristics of climatic and hydrological variables in the study area,revealing the abrupt change and periodic characteristics of various climatic factors.All natural factors had abrupt changes in 30 years,accompanied by periodic changes in varying degrees.The environmental flow components of Xiaolangdi station changed significantly from2007 to 2018 around 2013,During the period,there were 5 small floods,the peak value of high flow pulse showed an upward trend from 2007 to 2018,the maximum duration was less than 2.5 days,and the pulse frequency appeared at most in 2012,generating40 high flow pulses.(3)Temperature,light and total wetland area were negatively correlated,humidity,rainfall and runoff were negatively correlated,and the correlation between light and it was significant;temperature,humidity,light and runoff were negatively correlated with vegetation coverage,and rainfall was positively correlated with it,in which the correlation between light and vegetation coverage was the highest,and the other correlations were not obvious;temperature and ecological evaluation index were negatively correlated Humidity,rainfall and runoff are positively correlated with it,among which humidity has the highest correlation.The construction and operation of reservoir can change the ecological process of wetland by changing the characteristics of habitat and hydrological and hydraulic factors.To some extent,rapid urbanization leads to wetland area shrinkage and habitat fragmentation.(4)Based on the analysis of the construction of water conservancy projects in the middle and upper reaches of the Yellow River and the urbanization development process in the study area,and based on the analysis of many natural and human factors in the evolution process of wetland,this paper puts forward relevant wetland protection measures from two aspects of engineering measures and non engineering measures.