Evolutionary Process of the Yangtze River

Abstract

From the examination of the Yangtze River’s evolutionary history, tectonic movement was determined to be the original driving force for the geomorphology of the river. Additionally, climate change, especially the alternate occurrences of the fourth ice age and interglacial periods and the change of land vegetation, was an important part of the main forces that drove the development of the Yangtze River’s alluvial plain in the middle and lower reaches. The current river characteristics of the Yangtze River have resulted from the combination of the natural evolution and human activities. The agricultural development since the Neolithic age and the dike construction over the last 2,000 years have had far-reaching impacts on the channel in the diddle and lower reaches and the river-lake relationship. Based on tectonic movement and climate change, this chapter discusses the evolutionary process of Yangtze River’s formation and ecosystem since the uplift of the Qinghai-Tibet Plateau. Additionally, this chapter emphatically analyzes the important time nodes formed by the Yangtze River, such as the channeling through the Jinsha River and the Three Gorges, and the eventual formation of the overall west-east landform pattern of the Yangtze River. Next, this chapter summarizes the formation and evolutionary process of the Yangtze River, Dongting Lake, Poyang Lake, Yangtze Delta, and Tai Lake and finally performs a section-by-section analysis of the basic characteristics of the Yangtze River channel.

The timescale, or design base period, considered by hydraulic engineers in the watershed planning and hydraulic engineering design, is generally over a period of several decades to 100 years or so. In preparing a plan for flood control or drought relief, historical flood or drought events for up to 2,000 years need to be investigated. However, geographers and landscape ecologists need to consider the Quaternary period or more than two million years in analyzing the geomorphology of a river and the evolution of a regional landform. Geologists, paleontologists, and paleoclimatic scientists need to examine rocks, biological fossils, and glacier evolution on a timescale that needs to include geologic ages or tens of millions to hundreds of millions of years in studying the evolution of the earth and living things. The time and geometrical scales for different fields of study vary greatly. Therefore, it is necessary to use various timescales and different perspectives to study the river-ecological environment relationship and investigate the long-term effect of hydraulic projects on rivers so as to objectively and comprehensively understand the essence of the issues and predict the trend of the river evolution. Some of the Yangtze River’s rare and endemic fish species of concerns might first appeared on the earth tens of millions of years or even billions of years ago. According to the results of paleontological studies, marine fish species flourished on the earth as early as in the Devonian period 409–362 million years ago (Ma), and freshwater fish species, such as the Chinese sturgeon and other rare fish species of the Yangtze River, thrived in the Cretaceous period 135–65 Ma. As Chinese sturgeons appeared in those early ages, they were called “living fossils.” However, more studies will need to be performed on the relationship between the evolution of the Yangtze River and the evolution of aquatic organisms to answer the questions as to when the rare fish species started in the Yangtze River; where their early habitats were; and how their habitat environment is evolving at present and will evolve and be protected in the future. The beginning and evolution of living organisms in the Yangtze River basin are directly related to geographical, climatic, hydrologic, and habitat evolutions. Therefore, to protect the Yangtze River, it is necessary to understand the history of the river and analyze the current condition and predict the future condition of the river based on its history so as to better protect and manage the river.