| Summary: | Waterborne pollution from mining is impacting groundwater and surface water resources in many regions of the world. Main problems include acidification and high levels of dissolved toxic metals that adversely affect humans and ecosystems. Over the past millennium, mineral extraction has left behind vast amounts of waste rock, tailings and exposed rocks across landscapes that, in contact with air and water, risk generating acid mine drainage (AMD). In comparison with large-scale mining sites, the impacts of the numerous abandoned small-scale mines have received limited attention in the scientific literature, in particular in the Arctic region. Furthermore, whereas the immobilization and retardation of toxic substances through sorption and (chemical) precipitation have been relatively well investigated, less is known about the potential impact of microbial processes on the large-scale transport and retardation of AMD. Main objectives of this thesis are to improve the understanding of contributions from abandoned small mines to the waterborne mining pollution, and to determine how the spreading of AMD via ground- and surface water may be mitigated on catchment scales by microbial sulfate reduction (MSR), which is a process that transforms sulfate into sulfide and facilitates metal precipitation from the aqueous solution. Multiple field measurement campaigns were conducted in Arctic Fennoscandia to evaluate the water quality downstream of mining sites, and a data-driven sulfur isotopic fractionation and mixing scheme was developed to quantify field-scale MSR. Results showed that small abandoned mines could contribute disproportionately to downstream water pollution, as compared with larger mines. Copper mass flows in a stream passing the abandoned Nautanen mines (northern Sweden) was for instance found to be 450 kg/year one century after mine closure. Furthermore, across five study areas (both mining-impacted and reference catchments) spanning geographically from southern Sweden to the Kola Peninsula (Russia), MSR ...
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