Zhu et al. (1) complement our recent study on the characteristics and change of inland water bodies (WBs) in China (2) by further examining the epochal changes of three types of WBs larger than 1 km2. They first categorize these WBs into saline lakes, freshwater lakes, and artificial reservoirs based on multiple national lake/reservoir surveys, and then reexplore their area changes using the Global Surface Water Dataset (GSWD) following Feng et al. (2). Their results show some additional thematic details of the WB change in China.
Feng et al. (2) provide a synoptic view of China’s WBs and their dynamics at the national and basin scales, opening doors for much more research. The study by Zhu et al. (1) shows that more detailed analyses can be sprung from Feng et al. (2). In addition, we believe it is essential to use a holistic approach to detect the spatial, temporal, and thematic (i.e., transitions among water and nonwater land covers) changes of WBs in the context of landscape dynamics so that the driving forces and consequences can be elucidated and understood. Here we use the yearly dynamics of WBs and other land covers in the eastern Dongting Lake to demonstrate this point.
Dongting Lake, the second largest fresh lake in China at present and a globally important area for freshwater aquatic biodiversity, has undergone drastic changes in recent history (3). The water surface area of the Dongting Lake was 4,955 km2 in the 1930s, but decreased to 2,518 km2 in 1998, with a reduction of 49% (4). The main driving force of this change was massive impoldering (cropland reclamation) from the early 1950s to the end of the 1970s. This trend was later reversed by land transformation from cropland to WB, propelled by government policies designed for ecological restoration and flood control. Annual land cover maps from 1987 to 2019, produced at 30-m resolution using the continuous change detection and classification (CCDC) approach (5) and all available Landsat images, show more details of the WB changes in the eastern Dongting Lake (Fig. 1). Analysis of the land cover transitions reveals that WBs experienced the largest net change in area, decreasing 93.5 km2 or 7.4%. The largest change was found between cropland and WBs: Around 111.3 km2 of WBs were converted to cropland and, meanwhile, 56.5 km2 of cropland converted to WBs, resulting in a net loss of 54.8 km2 in WBs to cropland. Urban expansion (76 km2) was mainly at the cost of cropland and forest, with WBs contributed a small fraction (about 8%). Large wetland expansion (13%) was also observed in the eastern Dongting Lake, mostly from WBs. Such detailed holistic analysis of land cover change is necessary to understand the rates, patterns, driving forces, interactions of ecological processes, and consequences (6–10).
Fig. 1.
(A) Location of the Dongting Lake, (B) annual changes and cumulative net change of WB area, and (C) water body changes between 1990 and 2015 in the eastern Dongting Lake area. Annual land cover maps from 1987 to 2019 were produced at 30-m resolution using the CCDC approach and all available Landsat images. Other land covers were masked to highlight the changes related to water bodies. B shows strong interannual variability and the impact of the Three Gorges Dam at full operation since 2003.
Acknowledgments
This work was supported by research grants from the National Natural Science Foundation of China (Grant 41971152) and Hunan Innovative Talent Program (Grant 2019RS1062) to S.L., and the Scientific Innovation Fund for Post-graduates of Central South University of Forestry and Technology (Grants CX20190631 and CX20192037).
Footnotes
The authors declare no competing interest.
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