| Wetlands are known as the "kidney of the earth",and,wetlands,forests and oceans are three major ecosystems on Earth.It is not only an important natural resource,but also one of the most important living environments of mankind.It is an important foundation for human survival and sustainable development.On the one hand,wetlands can be used as a direct source of water or to supplement groundwater and soil desertification can be effectively prevented by them;on the other hand,runoff and microclimate can be regulated,water quality can be improved,biodiversity can be protected,tourism resources can be provided by wetlands.The Yellow River Delta is the broadest,most complete and the youngest wetland ecosystem in warm temperate zones in the world.The tidal channels are widely distributed among them.They are the intermediary of material exchange and information transmission between inland water and ocean.Based on remote sensing images and principle of landscape ecology,RS and GIS technology were used and some software like ENVI,ArcGIS and Canoco were adopted in this study.Combining with principal component analysis,multiple linear regression analysis and redundant analysis,the dynamic changes of tidal channels and landscape patterns in the Yellow River Delta from 1989 to 2016 were analyzed.The effects of tidal channels on the spatial distribution of typical wetland landscaped were studied,and the impacts of multiple stresses on the landscape types of the Yellow River Delta were revealed.Based on the spatial distribution of tidal channels from 1989 to 2016 by visual interpretation,the dynamic changes of tidal channel development in the Yellow River Delta wetland over the past 20 years were analyzed by calculating the spatial distribution,morphology and network structure of the tidal channels.The results showed that the total number of tidal channels first decreased and then increased,and the total length is in the fluctuating change of increasing and decreasing.The frequency of tidal channels was relatively small,and the tidal density had a fluctuation of decreases and increases.The curvature of the tidal channels was small,that is,the tidal channels were relatively stable.And the tidal channels had a fractal feature,but the network connectivity of the tidal ditch was generally low.Compared with the northern of the Yellow River Delta,the tidal channels in the southern were relatively well developed,but its network connectivity between the tidal channels was relatively poor.According to the characteristics of the wetland landscape in the Yellow River Delta,the wetland landscape of the Yellow River Delta was divided into five types:Phragmites australis,Suaeda salsa,mudflats,Spartina alterniflora and others.The landscape pattern analysis software was used to analyze the landscape pattern dynamics of the Yellow River Delta wetland over more than 20 years.The results showed that the wetland area in the Yellow River Delta was a fluctuation of increasing and decreasing.The landscape was fragmented and the shape tended to be simple.The area proportion of mudflats had been the largest,and the Suaeda salsa was the smallest.The change trend of the area proportion of Phragmites australis,Suaeda salsa was basically opposite to that of mudflats.It was the process of decreasing first and then increasing.The patch density of mudflats was the largest,and the patch density of Suaeda salsa was the smallest,that is,the degree of fragmentation of mudflats was the highest,and the degree of fragmentation of Suaeda salsa was the lowest.The patch shape and structure of Phragmites australis,Suaeda salsa,mudflats were relatively simple.Based on the typical landscape classification of the Yellow River Delta,the effects of tidal channel development,road construction and runoff on its variation were explored.In the past few decades,the road length in the Yellow River Delta had increased significantly,while the Yellow River runoff(Lijin station)had shown a significant downward trend.The higher the tidal channel development,the larger the wetland landscape area;the higher the Yellow River runoff,the smaller the landscape area.The roads had the greatest impact on the fragmentation of the Yellow River Delta landscape.The stronger the road construction activity,the higher the degree of landscape fragmentation.The tidal channels and roads had a negative effect on the proportion of Phragmites australis,Suaeda salsa,and the runoff had a positive effect on them.Road construction had a great positive influence on the shape and structure of Phragmites australis and mudflats.With the help of redundant analysis methods,the effects of various indicators of tidal channels on the changes of typical landscapes were explored in the Yellow River Delta.The results showed that there was a strong positive correlation between the tidal channel length and the overall landscape area,the fractal dimension of tidal channels and the perimeter-area fractal index of Phragmites australis,the frequency of tidal channels and perimeter-area fractal index of mudflats.The number,length and fractal dimension of tidal channels had a negative correlation with the area ratio,fragmentation degree and perimeter-area fractal index of Suaeda salsa.There was a large negative correlation between the number,length of tidal channels and fragmentation degree and area ratio of Phragmites australis.The effects of tidal density on the landscape pattern index was the smallest,and the number of tidal channels was the tidal zone index that contributed the most to the landscape pattern of the Yellow River Delta. |
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