Heterogeneity and influencing factors of algal blooms in the reservoir-impacted tributary: Evidence from remote sensing and physical-based model

The construction of reservoirs often caused algae blooms but there is controversy over pattern and attribution of blooms in reservoir-impacted tributaries due to lacking of detailed records. Herein, the remote sensing data with resolution of 10-meter pixels and physics-based model were combined to explore spatiotemporal distribution of algae blooms in key tributaries of Three Gorges Reservoir, China. Self-organizing maps were used for identifying the drivers of blooms. The results revealed that algae blooms were more serious during dry years and there was little difference between dry or wet years for multi-stage gate river with coverage remaining at 42.90%. The open waters with slow currents were identified as high-risk zones. Hotspots of algae blooms changed during the year, which were close to estuary in spring, upstream in autumn, and dispersed in backwater region in summer. Water level was major measure for managing algae blooms, while meteorological conditions were identified as the key factor (40.25%) for river with multi-stage dams and characteristics of shallow lakes. For the nutrients-rich river, blooms were driven by both water level (13.98%) and climate factors (23.34%). The blooms of natural backwater river were stimulated by combination of water level, climate and waterhed nutrients. These results highlighted necessity of region water quality management in reservoir-impacted regions.