Speciation Distribution Characteristic and Ecological Risk of Heavy Metals in Surface Sediments of Cascading Hydropower Dams in Lancang River

In order to study the speciation, contamination statues, and distribution characteristic of heavy metals in the surface sediments of cascading dams, the reservoir regions of Manwan and Dachaoshan cascading dams were sampled and investigated. The speciation and its contents of heavy metals (As, Cd, Cr, Cu, Pb, and Zn) were analyzed by the modified European Community Bureau of Reference (BCR) sequential method. The ecological risk assessment of heavy metals was performed by the ratio of secondary phase and primary phase (RSP) method. The source identification of heavy metals was performed by correlation analysis (CA) and principal component analysis (PCA). The results indicated that the values of RSPcd were from heavy pollution (IV level), and those of RSPZn were from light pollution (II level) to moderate pollution (III level) in the lacustrine zone of the upper-stream Manwan dam. The values of the RSP were no pollution (I level) in the downstream of the Dachaoshan dam. The ecological risk assessment of heavy metals (Cd, Zn, and As) at the upper stream of the Manwan dam was generally higher than that at the downstream Dachaoshan dam. Cascading dams operation showed significant accumulation effects on heavy metals in surface sediments. The source identification of heavy metals showed that Cd and Zn were mainly from anthropogenic activities; As, Cu, and Pb were affected by both natural processes and anthropogenic activities; and Cr was mainly from natural processes.