Contrasting Drivers of Water Clarity: A Multi-Decadal Satellite Analysis of Two Types of Lake Wetlands

Wetlands are unique ecological systems that exhibit both aquatic and terrestrial landscape characteristics. Wetland water quality is facing significant threats due to the combined impacts of climate variations and human activities. Therefore, analyzing the spatiotemporal dynamics of water clarity (Secchi disk depth, Zsd) across different types of wetlands, as well as revealing the relationship between driving factors and their responses, is crucial for monitoring and assessing variations in wetland water environments. The study utilizes Landsat data to analyze the spatiotemporal dynamics of Zsd and the response relationships of driving factors in typical flow-connected and non-flow-connected lake wetlands since 1984, focusing on Dongting Lake (DTL) and Poyang Lake (PYL) as examples of river-flow lake wetlands, and Baiyangdian Lake (BYD) and Hengshui Lake (HSL) as examples of non-flow-connected lake wetlands. The findings reveal that the variations in Zsd and the spatial variability in river-flow connected lake wetlands are greater than those in non-flow-connected lake wetlands, which may be attributed to abundant precipitation and frequent water exchanges. In terms of interannual scale, distinct stages of increase and decrease in Zsd are observed, characterized by peak values followed by declines. These interannual variations are driven not only by climate fluctuations but also by variations in landuse and landscape. Through quantitative analysis of the spatiotemporal dynamics of Zsd in various wetland types, the study further explores the driving mechanisms and the differing responses of climate factors, landuse, and landscape to Zsd variations in river-flow and non-flow-connected lake wetlands. The research provides a data foundation and scientific support for monitoring and managing water resources in large-scale wetlands under the dual impacts of climate variability and human activities.