Widespread decrease in chromophoric dissolved organic matter in Chinese lakes derived from satellite observations

Chromophoric dissolved organic matter (CDOM) can significantly influence underwater light fields, nutrient availability, and microbial activity; thus, it plays an essential role in physical, chemical, and biological processes in aquatic ecosystems. China has undergone significant changes in climate, water quality improvement, and human processes over the past few decades. However, the impact of these processes on CDOM in Chinese lakes is unclear. Therefore, in this study, we aimed to reconstruct long-term and high-resolution CDOM data from Landsat satellite images using a simple model to characterise changes in CDOM in 2462 Chinese lakes (surface area >= 1 km(2)) from 1986 to 2021. Validation results demonstrated that the model performed adequately in deriving the CDOM absorption coefficient at 350 nm, with a root mean square deviation, median deviation, median absolute percentage difference, and median ratio of 0.68 m(-1), 0.02 m(-1), 19.76%, and 1.01, respectively. We observed a distinct spatial pattern of CDOM, with higher CDOM in eastern China with intensive human activities but lower CDOM in western China with strong ultraviolet radiation. Temporally, mean a(CDOM)(350) of Chinese lakes from 1986 to 2021 decreased at a rate of - 0.25 m(-1)/10 years. We also revealed that increased regional vegetation coverage and improved water quality mainly drive CDOM decline in lakes on the Qinghai Tibet Plateau Region and Eastern Plain Region, respectively. The widespread decrease in CDOM, in turn, has contributed to changes in the optical properties and biogeochemical cycles of Chinese lakes. Our results provide valuable insights for lake environmental protection and water quality management in China