Determining the priority control factor of toxic metals in cascade reservoir sediments via source-oriented ecological risk assessment

Determining the priority control factor is crucial for managing sediment toxic metals (TMs) pollution. Therefore, the vertical profiles of TMs in core sediments from the Nuozhadu (NZD) and Jinghong (JH) cascade reservoirs in the Lancang River were studied to assess the source-oriented ecological risks. The geo-accumulation index (I-geo), enrichment factor (EF), potential ecological risk factor (Er), and potential ecological risk index (RI) were employed. Then, combined with principal component analysis (PCA) and the positive matrix factorization (PMF) model, the effects of TMs and contamination sources on ecological risks were revealed. Results showed that the concentrations of As, Cd, Hg, Pb, and Zn in the NZD Reservoir were significantly lower than those in the JH Reservoir, which might be related to the coarser grain size of the NZD Reservoir sediments. While both reservoirs demonstrated elevated contamination levels of Cd and As among all the TMs, the NZD Reservoir also exhibited high levels of Cr, whereas the JH Reservoir showed relatively high levels of Hg. Natural and anthropogenic sources of TMs were quantitatively identified in cascade reservoirs. Cd and Hg exhibited higher ecological risk levels than other TMs in both reservoirs. The JH Reservoir was exposed to significantly higher ecological risks from TMs compared to the NZD Reservoir, and 40.0 % of the sediments in the JH Reservoir were exposed to considerable risk (300 < RI < 600). Results of source-oriented ecological risks showed that Cd from anthropogenic sources was identified as the priority control factor in the NZD and JH cascade reservoirs. Our findings give scientific backing for the prevention and control of TM contamination and the planning of sustainable development of water resources in the Lancang-Mekong River.