Small 110-year old mine in northern Sweden leaves disproportionately high metal impact on water quality

Pollution from small abandoned mines is usually overseen compared to larger historical mining sites. Especially in the Arctic more research is needed on long-term water quality degradation from mine waste (e.g. metal leakage). We have studied changes in water quality from a historical copper (Cu) mining area, Nautanen, northern Sweden, that was shortly in operation for six years before abandonment in 1908 (~110 years ago). Water quality data from previous studies of the site (1993-2014) was compared to results from our own field campaigns in 2017, which provided us with a rare Arctic case study of 25 years of data. The results showed Cu, Zn and Cd concentrations at the mining zone being orders of magnitude larger than local background levels. This was surprising considering Nautanen’s short time of operation, the small scale of the mining site, and the long time since closure. We found no declining trend of metal concentrations over the surveyed 25-year period (1993-2017) and during the past 110 years (1907-2017) a mass flow of 43 tons of Cu was estimated to have been released to the local surface water system from the mining zone and 7 tons of Cu at 4 km downstream. Nautanen stands out with its high metal leakage relative to its small volume of mine waste compared to mass flows of other larger historical mining sites in e.g. Sweden and Canada. Small abandoned sites, which are numerous, could add disproportionately large amounts of metals to surface water systems. This information is crucial in upscaling local low-priority sites to regional assessments of total pollution pressures in sensitive Arctic environments. We are currently further investigating pollution transport pathways through oxygen and sulfur isotopes to trace water originating from the mine and other sources (e.g. atmospheric deposition, bacterial sulfate reduction). This method could give valuable information in data scares sites where e.g. groundwater data is inaccessible.