Remediation of Metal-Contaminated Shallow Wetlands: Hydro-Biogeochemical Controls and Sustainable Treatment Strategies

Shallow wetlands retain metals and metalloids from industrial, mining, agricultural, urban, and atmospheric sources; however, shallow water columns, active sediment–water exchange, and recurrent wetting–drying also favor remobilization. This critical narrative review evaluates physical, chemical, biological, and ecological engineering approaches for metal-contaminated shallow wetlands, focusing on the hydrological and biogeochemical conditions governing performance. Evidence was differentiated among natural or semi-natural wetlands, engineered wetland analogues, and transferable studies of contaminated sediments, soils, or wastewaters. Physical interventions rapidly control localized sediment inventories but can disturb habitats and redistribute particles. Chemical amendments reduce porewater concentrations and bioavailability, although durability depends on pH, redox conditions, dissolved organic matter, and competing ions. Biological and ecological engineering approaches can support ecological function recovery, but performance depends on plant traits, microbial processes, hydroperiod, and maintenance. No intervention was consistently superior across site conditions and outcome domains. Within this framework, sustainability is evaluated through durable risk reduction, ecological function recovery, life-cycle feasibility, responsible residual management, and accountable long-term stewardship. The reviewed mechanistic and conceptual evidence supports considering site-specific treatment trains, although direct comparative field evidence demonstrating their superiority over individual interventions remains limited. Future studies should prioritize hydrologically realistic field validation, standardized flux and bioavailability endpoints, mixed-contaminant scenarios, life-cycle assessment, and explicit measurement of ecological function recovery.