Differentiated Characteristics of Suspended Particulate Matter and Their Effects on Water Quality in the Middle and East Routes of the South-to-North Water Diversion Project

• • Middle Route SPM is dominated by coarse particles (>63 μm, 61.43%–94.68%) with TP <0.01 mg·L−1, indicating low nutrient levels and algal-driven aggregation; this necessitates targeted algal bloom control to prevent deposition and potential nutrient release. • • East Route SPM is dominated by fine particles (<20 μm, 51.26%–88.61%) with TP ranging from 0.03 to 1.11 mg·L−1, reflecting high external nutrient loading; fine particles enhance nutrient adsorption, requiring sedimentation and wetland strategies to mitigate pollution. • • Carbon and nitrogen isotope analysis shows that Middle Route SPM is predominantly autochthonous (algae contribution >46.75%), whereas East Route SPM is a mix of terrestrial C3 plants and algae, indicating different source management priorities. • • Chlorophyll a correlates significantly with coarse particles (r=0.60) in the Middle Route, confirming that algal aggregation is a key mechanism for particle formation; this correlation can be used as a monitoring indicator for algal proliferation and water quality management.