| Hanjiang River Basin covers an area of 159,000 square kilometers,spanning five provinces and cities such as Hubei and Shaanxi,which is an important habitat for rare species such as crested ibis and one of the water sources of the South-to-North Water Transfer Project.Hence,It is an important support for the circulation and integration of resource elements among different regions and the healthy development of regional population,and plays an extremely important role in maintaining ecological balance.Due to the climate change and unreasonable utilization of human beings,the wetland is facing serious ecological problems.In recent years,more and more attention has been paid to the study of wetland degradation in Hanjiang River Basin.In this study,remote sensing images of the Hanjiang River basin in seven periods of1990,1995,2000,2005,2010,2015 and 2020 are used as the main data sources,combined with digital elevation data,zoning information and yearbook information of Shaanxi Province,and based on a reasonable classification of wetlands in the Hanjiang River basin,the area,structure and functional change characteristics of wetlands are taken as a starting point,and remote sensing technology is used to The changes of wetlands in the basin were monitored in the past 30 years based on remote sensing technology.And using the hierarchical analysis method(AHP),combined with the characteristics of wetland changes in the past 30 years,a comprehensive evaluation framework of wetland degradation was built based on seven indicators: wetland area change rate,habitat quality,landscape dimensionality,landscape patch number,landscape shape index,landscape aggregation,landscape spreading,using TOPSIS method to make a comprehensive evaluation of wetland degradation,from the basin as a whole to the key sub-basin to make a comprehensive evaluation of the degree of wetland degradation at different levels.The degradation degree of wetlands is evaluated in a hierarchical manner.We also combined the socio-economic data such as roads,population,GDP and natural environment related data such as annual precipitation and average annual temperature in the study area,and used BUDYKO theory and PLUS model to determine the main driving factors of wetland degradation.The main conclusions obtained here are as follows:(1)Through field research,it was found that the spatial distribution of wetlands in the basin was uneven.The topography of the Han River basin in Shaanxi province is from upstream to downstream,and the slope of the riparian zone transitions from low to high.Wetlands in the Han River basin are mainly distributed in the Han River Wetland Provincial Nature Reserve in Shaanxi.Based on the topography of the river basin,the Shaanxi section of the Han River basin was divided into 41 sub-basins according to the catchment area.Combined with the field research results,the average slope of the riparian zone was used as the discriminant condition to determine that wetlands are mainly distributed in sub-basins with an average slope of less than 20°.(2)The wetland area in the Shaanxi section of the Han River basin has shown a trend of increasing and then decreasing over the past 30 years,and the wetland area in the basin decreased the most by 17.4% during 2010-2020.30 years of wetland change in the basin can be divided into two stages,with a relatively gentle change in wetlands from 1990 to 2005 and a dramatic change in wetlands after 2005.Spatially,the decrease of wetlands in the upper part of the basin is particularly obvious,and the wetland area of sub-basins located in the upper part of the basin shows an overall trend of increasing and then decreasing,while the wetland area of sub-basins located in the lower part of the basin shows an increasing trend.The sub-basin with the largest decrease in wetland area is located in the upper part of the basin,where the area decreased by 211.5 ha over a 30-year period,with the most dramatic change between 2005 and 2010.(3)The overall trend of patchiness in the wetlands of the Han River basin over the past 30 years has shown an upward trend,and indicators such as landscape shape index,aggregation and spreading have been relatively stable for 30 years.Spatially,the sub-basin with the largest increase in the number of patches is located in the upper reaches of the basin,the number of patches in the basin was stable before 2000,and gradually increased after 2005,the patches in the sub-basin increased by 19.2% between2005 and 2020,and the degree of fragmentation increased.The sub-basin with the highest decrease in spreading index is located in the downstream,with a 5.2% decrease in spreading index over 30 years,with the sharpest decrease between 2005 and 2015,indicating that the connectivity between landscapes in this sub-basin has been damaged to some extent during this period.(4)Based on the In VEST model,we analyzed the habitat quality of the Shaanxi section of the Han River basin,and the results showed that the habitat quality of the basin showed a trend of first decreasing and then increasing over 30 years.Habitat quality in the basin was spatially low in the upper reaches and high in the lower reaches,and the areas with low habitat quality indices showed significant aggregation in the upper reaches,indicating that the upstream habitats were under more concentrated stress.(5)Based on the hierarchical analysis method,a comprehensive evaluation model of regional wetland degradation was constructed,and a comprehensive evaluation of wetland degradation in each sub-basin was conducted.The results showed that sub-basin 36,which is located in the downstream,has the highest comprehensive score,specifically in terms of increasing wetland area,stable patchiness and habitat quality,complex landscape boundary,and weakened by human interference;sub-basin 21,which is located in the upstream,has the lowest comprehensive score and is the key area of wetland degradation in the basin,specifically in terms of decreasing wetland area,fragmentation of the landscape,and decreasing habitat quality.(6)Through correlation analysis,it was found that the degradation drivers of wetlands in the basin varied greatly at different spatial scales.There was no significant correlation between the overall wetland degradation in the basin and each driving factor,and in the 21 sub-basin,where the wetland degradation was the most serious,the wetland indicators showed significant correlation with population and GDP,indicating that human activities were the main driving force of wetland degradation.Based on the PLUS model and BUDYKO theory,the quantitative analysis of wetland degradation drivers in 21 sub-basins showed that the change of substrate was the main reason for the difference of wetland degradation in different basins,and the contribution of four drivers to wetland degradation among the drivers in 21 sub-basins,namely,population,temperature,topographic slope and distance from secondary roads,reached more than50%,with the percentages of The quantitative analysis of the drivers showed that anthropogenic factors were the main factors of wetland degradation.Among them,the distance of wetlands from secondary roads is an important factor in relation to wetland degradation,and the planning of secondary roads is especially important for wetland protection. |
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