Regional sulfur isotopic end-member data (c_dep ,δ_dep and δ_rock ) for the Kola Peninsula and northern Sweden is summarized in Table 1. The Kola Peninsula showed higher average annual c_depcompared to northern Sweden. It is likely the result of nearby smelter emissions of sulfur dioxide (Forsius et al., 2010; Reimann et al., 1997), while the also higher δ_dep has been attributed to processing of high sulfide ores, which were transported from the Norilsk mine in north central Russia to Kola smelters (de Caritat et al., 1997). No

data was found on the specific δ_rock -value of sulfide bedrock in Khibiny. We argue that since the Khibiny bedrock is of magmatic origin (Kogarko, 2018) – as is the bedrock in the Imetjoki catchment – sulfide minerals in Khibiny would most likely also haveδ_rock -values close to 0‰ justifying the use of the isotopic dataset for Imetjoki also for the Khibiny catchments (Table 1). A reasonable range for the enrichment factor (ɛ) in shallow groundwater and surface waters was assumed to be −33 to −1‰, considering that most studies report values between −20‰ and −10‰ (Knöller et al., 2004; Robertson and Schiff, 1994; Wu et al., 2011) while some estimates reach as low as −33‰ (Massmann et al., 2003), and as high as −1‰ (Xia et al., 2017).