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Evaluation of the Impacts of Land Use on Water Quality: A Case Study in Erhai Lake Basin

Erhai Lake, the second largest freshwater lake in the Yunnan Province of China, has the flourishing tourist industry. Unfortunately, many problems such as deterioration of water quality and eutrophication were occurred in Erhai Lake, leading to numerous environmental problems. Chlorophyll-a (chl-a) and water transparency are critical ecological and environmental parameter for water quality, which play the important roles in the wetland environment and eutrophication of water. Human-induced land-use change can indicate the degree of the interference of anthropogenic activities on the regional ecological environment. Therefore, understanding the relationships between changes in land use and water quality is of great importance to improve water pollution control and for providing guidelines for land use planning. However, the effects of ongoing anthropogenic activities on water quality in Erhai Lake Basin are not well understood. Closing this knowledge gap first requires obtaining the accurate land use change information. A Random Forest classifier could be applied to spectral as well as textural features extracted from time-series of Landsat MSS/TM/ETM+/OLI imagery, ranging from 1973 to 2020, to increase the accuracy of land cover classification. The classification results show the spatiotemporal patterns and characteristics of land-use change in Erhai Lake Basin. Besides, the Landsat TM/ETM+/OLI, Medium Resolution Imaging Spectrometer (MERIS), MODIS (moderate resolution imaging spectroradiometer) and Sentinel-3 OLCI satellite data were used to estimate the chl-a concentration and water transparency in Erhai Lake from 1985 to 2020. Long-term water transparency and chl-a distributions of Erhai Lake revealed the changing trend of water quality. We use the geographically weighted regression (GWR) model to identify the impact of land-use change on chl-a concentration and water transparency. The land use change has a direct impact on water quality varied over nearly five decades; both positive and negative effects for certain land-use types were found in Erhai Lake Basin. These findings shed new light on the impact changes of land use on water quality and provide a scientific foundation for land use management and remediation plans.