Abstract
Tracking cropland change and its spatiotemporal characteristics can provide a scientific basis for assessments of ecological restoration in reclamation areas. In 1998, an ecological restoration project (Converting Farmland to Lake) was launched in Dongting Lake, China, in which original lake areas reclaimed for cropland were converted back to lake or to poplar cultivation areas. This study characterized the resulting long-term (1998–2018) change patterns using the LandTrendr algorithm with Landsat time-series data derived from the Google Earth Engine (GEE). Of the total cropland affected, ~447.48 km2 was converted to lake and 499.9 km2 was converted to poplar cultivation, with overall accuracies of 87.0% and 83.8%, respectively. The former covered a wider range, mainly distributed in the area surrounding Datong Lake, while the latter was more clustered in North and West Dongting Lake. Our methods based on GEE captured cropland change information efficiently, providing data (raster maps, yearly data, and change attributes) that can assist researchers and managers in gaining a better understanding of environmental influences related to the ongoing conversion efforts in this region.
Highlights
Dongting Lake, once the largest freshwater lake in China, has shrunk to the second-largest due to land reclamation for agriculture; this has resulted in serious ecological degradation of the area’s wetlands [1]
We showed the effectiveness of a trajectory-based change detection approach to characterize two cropland change patterns in China’s Dongting Lake region
By using the LandTrendr algorithm with Landsat imagery derived from the Google Earth Engine, we detected and mapped the conversion of cropland to lake and poplar cultivation with overall accuracies of 87.0% and 83.8%, respectively
Summary
Dongting Lake, once the largest freshwater lake in China, has shrunk to the second-largest due to land reclamation for agriculture; this has resulted in serious ecological degradation of the area’s wetlands [1]. After the devastating flood in 1998, the government promoted the project of Converting Farmland to Lake (CFTL) and planned to abandon 785.7 km of cropland area, where conversion to lake or poplar trees cultivation could establish a new balance between economic benefits and the regulation of wetland ecological functions. These efforts have created a need for long-term monitoring of cropland change processes to provide scientific data for ongoing ecological management after project completion. Zhe [14] provided a comprehensive review of change detection approaches using Landsat time-series data, including the description of frequencies, preprocessing, algorithms, and applications
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