Tracing pollution legacies in the Suances Estuary (N Spain): Challenges for dating methods and ecological recovery after mine closure

Estuaries are globally threatened ecosystems, requiring urgent assessment of their historical deterioration and recovery processes to inform realistic strategies for sustainable management. This study employs an integrated, multidisciplinary approach, including analyses of trace metals, foraminifera, and radionuclides in surface samples and short (47 cm) sediment cores, to evaluate the environmental evolution of the heavily polluted Suances Estuary (N Spain) and its response to the cessation in 2003 of historical mining activities of one of Europe’s largest carbonate-hosted Pb-Zn ores, the Reocín metalliferous deposits. Core samples showed elevated concentrations of Zn (maximum value >10,000 mg kg⁻¹), Pb (max. 2700 mg kg⁻¹), Cd (35.3 mg kg⁻¹), and Hg (41 mg kg⁻¹), exceeding local background values and often surpassing Sediment Quality Guidelines. Despite an overall decrease in metal concentrations from surface samples between 2003 (max. value of Zn: 11,200 mg kg⁻¹; Pb: 2200 mg kg⁻¹; Cd: 26.4 mg kg⁻¹) and 2022 (max. value of Zn: 8520 mg kg⁻¹; Pb: 990 mg kg⁻¹; Cd: 20.5 mg kg⁻¹), significant spatial variations suggest sediment redistribution within the estuary. Moreover, foraminiferal abundances remain extremely low (range of standing crops: 1–510 individuals per 80 cm³), indicating persistent unfavorable environmental conditions for life and reproduction. Abnormal ²¹⁰Pb_xs signals in the sedimentary record unveil the impact of anthropogenic events related to the development and subsequent abandonment of mining activities. These findings underscore the complexity of sediment chronologies and environmental responses in historically contaminated estuarine systems, highlighting the need for long-term monitoring programs within a multidisciplinary framework.