Identification of Degradation Process of Chenhu Wetland over Last 50 Years

Chenhu wetland is a typical freshwater lake-type wetland in the Middle-Lower Yangtze Plain, and has severely degraded since 1960s. In this study, aerial photographs or remote sensing images captured at eight different stages (i.e. 1964, 1975, 1987, 1997, 1998, 2007, 2016 and 2018) were analyzed to reveal the degradation processes and mechanisms of the Chenhu wetland in Wuhan over the past 50 years by the aid of remote sensing, dynamic degree models and transition matrix models.Our investigation reveals that the Chenhu wetland was gradually altered to fish ponds or agricultural lands from north to south, shrunk up to 77% in total between 1964 and 2018. Degradation of the Chenhu wetland by human impacts during this period can be divided into three stages: (i) between 1964 and 1975, degradation was dominated by filling of lakes into agricultural lands, with the rate of agricultural lands expansion exceeding 141%; (ii) between 1975 and 1994, artificial lake reconstruction projects has altered large areas of lakes into marshes; (iii) between 1997 and 2018, new marshes altered from lakes were further cultivated into agricultural lands or reserved as fish ponds. In general, population expansion and changes in land use policies have caused the degradation of ecosystem services, including impaired capacity in flood regulation and storage, natural self-purification and biodiversity losses. The degradation modes uncovered for the Chenhu wetland can also shed light on similar investigations on the degradation of other lake-type wetlands in Middle-Lower Yangtze Plain and even the whole China.