Impacts of winter heatwaves on water quality in mining-affected environments

Sammanfattning

Climate change is leading to warmer and more variable winters in northern Europe, resulting inan increasing occurrence of winter heatwaves (WHWs), characterized by unusually high wintertemperatures. At the same time, mining-affected environments represent significant sources ofcontaminants in surface waters. This study investigates how changing winter conditionsinfluence water quality in a mining-affected area in south-central Sweden, with a particular focuson the relationship between winter heatwaves and metal transport in surface waters. The study is based on climate data from 1977–2025 and water quality data from 2013–2024collected at an active mining site. In addition, supplementary field sampling was conductedduring the winter of 2026. The results show that winter heatwaves have become more frequentover time, while a slight increase in intensity can also be observed. The findings indicate that variations in winter temperature and the occurrence of winterheatwaves may influence hydrological and geochemical processes controlling the transport ofmetals and sulfate in the study area. Several water quality parameters varied in relation totemperature conditions, although the relationships differed among metals and samplinglocations. Depending on the contaminant and the conditions, the study suggests that processessuch as freeze–thaw cycles, altered winter runoff, and varying geochemical conditions mayinfluence contaminant mobilization and transport during winter periods. This work highlights how a warmer and more variable winter climate may affect water quality inmining-affected environments. Although the relationships between winter heatwaves and waterchemistry remain complex and partly uncertain, the increasing occurrence of such events mayhave implications for future contaminant transport and water resource management.