Effect of past century mining activities on sediment properties and toxicity to freshwater organisms in northern Sweden

Abstract

The release of toxic metals from local mining activities often represents a severe environmental hazard for nearby lake ecosystems. Previous studies on the impact of mining activities and the recovery thereof have primarily focused on single lakes. However, little attention has been focused on assessing spatial and temporal recovery patterns of multiple lakes within the same catchment but with different hydrological settings and distance to the pollutant source. This knowledge gap prevents us from assessing the real environmental risk of abandoned mines and understanding ecosystem recovery. This study explores the intensity and spatial patterns of sediment contamination and the potential for ecosystem recovery in three lakes in close vicinity of a lead (Pb) and zinc (Zn) mine that has been inoperative for more than 20 years. Dated (²¹⁰Pb and ¹³⁷Cs) sediment cores were used to reconstruct temporal patterns in trace element deposition and relate those with past mining activities. All lakes displayed increased Pb and Zn concentrations after the start of mining operations, coincident with a decrease in organic matter content. Lakes used as clearing ponds received higher loads of Pb, with a sharp increase in Pb concentration occurring when tailing ponds were constructed and a decline after the cessation of mining. Zn concentrations increased gradually from the beginning of the mining operation to the present. The estimated probable effect concentration quotient (PEC-Q) indicated severe toxic effects throughout the mining and post-mining period, but with spatial and temporal differences between the lakes. Although normalized PEC-Q to organic matter content decreased during post-mining conditions, sediment Pb concentrations were still >10 times higher than pre-mining values. This study highlights the importance of considering spatial and temporal heterogeneity of local impact from mining activities, both in metal load and sediment properties, to better assess lake-specific ecosystem responses and recovery from metal contamination.