Risk Assessment of Heavy Metal Pollution Characteristics in Environmental Dredging Sediment from Dianchi Lake under Multi-Scenario Land Use
Sediment risk assessment for lakes and rivers often neglects the distinction between in-situ ecological risks and ex-situ comprehensive utilization risks. This study proposes a multi-scenario risk assessment model incorporating both in-situ and ex-situ contexts. For the in-situ scenario, a dual-background-value potential ecological risk assessment was applied using national and Yunnan soil background values. For ex-situ scenarios, pollution risk assessment models were established for agricultural land (paddy and other) and construction land (Class I and II). Taking the Dianchi Lake dredging project as a case study, 92 sediment samples from polluted and transition layers at 46 grid points were analyzed for six heavy metals (As, Hg, Cd, Zn, Cu, Cr). Results showed: (1) Under different background values, ≥97.83% of samples exhibited moderate or higher ecological risk, with Hg and Cd as main contributors, Hg posing higher risk. (2) In agricultural scenarios (paddy/orchard and other), 95.65% of points had unacceptable risk, with comprehensive pollution intensity order Cd>Cu>Zn>As>Cr; for Class I construction land, As was the target pollutant with 93.48% of points unacceptable, while Class II land was acceptable. (3) Spatial heterogeneity was significant: horizontal risk was higher at the lake outlet than at the Cixiang River inlet; vertical risk was higher in the polluted layer than in the transition layer, with Hg and Cd potential ecological risk coefficients 11.58% and 24.19% higher, and comprehensive potential ecological risk index 43.27% higher. Pollution coefficients for Cd, Zn, Cu (agricultural) and As (Class I construction) increased by 123.02%, 6.3%, 4.1%, and 41.02% in the polluted layer. (4) Different evaluation methods yielded significantly different results, indicating that metals without potential ecological risk may still pose pollution risk in utilization scenarios, necessitating comprehensive consideration in remediation.