Spatial and Temporal Changes in Wetland in Dongting Lake Basin of China under Long Time Series from 1990 to 2020

Wetland plays a pivotal role in sustaining ecosystems and adapting to climate change. This paper used remote sensing images from 1990, 2000, 2010, and 2020 to investigate the changes in wetland in the Dongting Lake Basin (DLB) and their possible causes. The land-use conversion matrix and contribution rate were calculated in 1990-2000, 2000-2010, and 2010-2020, and results showed that the total wetland area displayed an increasing trend, especially the reservoir ponds and channels across DLB from 1990 to 2020. Forest and agricultural land conversion into wetland accounted for the main proportion, with the greatest contribution rate (234.13%) of forest land and the smallest rate (-117.46%) of agricultural land between 1990 and 2000. On the contrary, agricultural land had the highest contribution rate (47.96%) for wetlands compared to other land-cover types from 2000 to 2010, followed by forest land (39.03%). The contribution rates of forest and agricultural lands to wetlands were 60.17% and 39.02% from 2010 to 2020, respectively. Wetlands showed a more significant net gain (a total of 259 km(2)) in Central and Southern Hunan Province. More specifically, the wetlands area in North Hunan Province decreased by 45 km(2) from 1990 to 2000. It increased over the next two decades (155 km(2) and 22 km(2), respectively). Southern Hunan Province continued increasing from 1990 to 2010 (a total of 149 km(2)) while decreasing from 2010 to 2020 (a total of -297 km(2)). Forestation was the principal driving force promoting the continuous increase in wetlands. In addition, agricultural land was mainly related to wetland change in this region, characterized by reclaiming land from lakes in the earlier period and returning agricultural land to wetland in the later period. Built-up land occupied a small area of wetlands over the study period. The study is beneficial to understanding the wetlands' dynamic changes in the past and present, as well as being useful for wetland management, consistent with sustainable development.