Study of Historical Changes of Lake landscape in the Middle Reaches of the Yangtze

摘要

Jianghan Plain is one of the most important lake regions in the middle reaches of the Yangtze River in China. Over thousands of years, there has been a dynamic relationship between human impacts and the lake-river system, especially in the second half 20th century. Here, we analyze lake evolution in Jianghan Plain in the last fifty years with lake size large than 0.1 km2 by using drainage network and relief maps, historical maps and gazette, and remote sensing images of different periods. Historical changes of lakes were evaluated by total area, total number, annual variation rate in the whole regions and the area and number in four scale levels (0.1-1km2, 1-5 km2, 5-10 km2 and >10 km2) using a time series of lake maps. Lake landscape pattern dynamics were assessed by the landscape index of FRAC_AM which can reveal the change processes and features of lake shape by human impacts. The results show that during the second half of the 20th century there has been a general trend of significantly decreasing in lake area and number and the elimination of the large size lakes was the key to the rapid reduction of total area. The value of FRAC_AM was gradually increasing with the lake scale levels in every period except 1995. In the past fifty years, the FRAC_AM of large scale lakes decreased to minimum and that of other scale lakes did not have the law. The study indicates that the decrease in lake area in Jianghan Plain is caused by land reclamation and excessive soil erosion and sedimentation while the human impacts are likely the main factor. The reproduce of lake change process will benefit the ecological restoration and rehabilitation of lake area in the middle reaches of the Yangtze.