Spatial and temporal variability of physicochemical characteristics in Lancang River sediments amid hydropower...

The construction of river dams disrupts river continuity and sediment transport, altering the riverbed between sediment "sources" and "sinks" and changing the sediment characteristics of the river. In this study, 256 sediment samples from 54 major control cross-sections of the Lancang River (LCR) were analyzed to examine the spatial and temporal distribution of clay and non-clay minerals in the sediment and their relationship with the environmental changes caused by the construction 11 hydropower plants. The results indicate that the construction of terrace dams on the LCR interrupted the downstream refinement trend of sediments, which reappeared once the terrace reservoirs stabilized. Additionally, the interception of the dam increased the accumulation of clay mineral in sediments. From 2011 to 2023, the relative abundance of clay mineral in the regulated reaches (RRs) increased by 2.4 %, the quartz content decreased by 26.2 %, and the contents of calcite, mica, kaolinite, and chlorite increased, respectively. Consequently, the main non-clay mineral assemblage in the sediments shifted from quartz+feldspar to quartz+feldspar+mica. Furthermore, the clay mineral content was higher upstream the main dams (15.3 %) than downstream (14.8 %), with the sediment quartz and calcite contents being higher downstream, and mica and chlorite contents being higher upstream. The feldspar content showed a minimal change. However, the mineral composition of the sediments in individual reservoirs varied significantly, owing to the specific environmental conditions of each reservoir. The distribution of sediment clay also differed between the dry and rainy seasons. This study provides a scientific basis for managing reservoir sediment scheduling and regulating the ecological and environmental safety in watersheds.