Evolution characteristics of river longitudinal connectivity within Yangtze River basin in the past 60 years
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Abstract:
In the context of ecology,river connectivity refers to the smoothness of the transfer and diffusion of materials,energy and organisms among the various components of the river system.With the development of society and economy,the rapid human development and utilization of water resources has led to the decline of water systems and obstructed river connectivity in many river basins,which has seriously affected the function of rivers,such as maintaining the water body′s capacity of holding pollution and self-purification,ensuring the habitat of aquatic organisms and fish migration.As an important area of the national future development strategy,conducting evaluation and analysis about longitudinal connectivity of rivers within the Yangtze River basin to reveal its temporal and spatial evolution characteristics has great significance to the future construction of water conservancy projects and the protection and restoration of water ecosystems. Three different evaluation methods are adopted to explore the evolution characteristics of the rivers longitudinal connectivity within Yangtze River basin by taking construction data of four types of river blocking structures including reservoirs, hydropow-er stations,sluices,and rubberdams. Among them,the barrier coefficient method focuses on barrier characteristics of blocking structures on material flow,biological flow,energy flow,and information flow.The longest continuous reach ratio method focuses on embodying the distribution characteristics of blocking structures and their impact on suitable habitat areas for aquatic organisms represented by fish.The regional overall method focuses on the overall evaluation of the river′s longitudinal connectivity of the water resources regions（class Ⅱ）within the Yangtze River basin. Evaluation results of barrier coefficient method： among the 45 major rivers,in 1960,except Fu River and Xin Jiang,the longitudinal connectivity of the other 43 major rivers are rated as excellent.In 1980,37 rivers are rated as excellent,in 2000,there are 9 rivers with poor longitudinal connectivity while in 2018,the number has increased to 30.Evaluation results of the longest continuous reach ratio method： among the 45 major rivers,in 1960,the longitudinal connectivity of 41 rivers are rated as excellent.In 1980,there are 27 rivers with excellent evaluation grades.In 2000,there are 14 rivers with inferior evaluation grades.In 2018,there were 15 rivers each with poor evaluation grades.Evaluation results of the regional overall method： among the 12 water resources regions (class Ⅱ),in 1960,12 water resources regions (class Ⅱ) have excellent evaluation grades.In 1980 and 2000,there are 7 water resources regions(class Ⅱ) with excellent evaluation grades.In 2018,there are 3 water resources regions(class Ⅱ) with poor evaluation grades. The evaluation results of the barrier coefficient method and the longest continuous reach ratio method show that:In the time dimension,the longitudinal connectivity of rivers within the Yangtze River basin has gradually declined in the past 60 years,and the deterioration of longitudinal connectivity from 2000 to 2018 was the most significant,In spatial distribution,rivers with inferior evaluation grades are mainly distributed in three water resources regions (class Ⅱ)including Mintuo River water resources region,Jialing River water resources region,and Dongting Lake water resources region.The evaluation results of the regional method show that the longitudinal connectivity of the water resources regions (class Ⅱ) within Yangtze River basin deteriorated integrally in 2000-2018,and the overall regional connectivity of the western part of the Yangtze River basin is less damaged by the river blocking structures than the eastern part.Compared with large and medium-sized water conservancy projects,small water conservancy projects have more damage to the longitudinal connectivity.It is recommended to withdraw from the small hydropower stations in the Yangtze River basin in a reasonable and orderly manner.
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