Properties and Stability of Mining-Induced Meromixis in Two Small Boreal Lakes in Eastern Finland

Abstract Mine waters are a significant point source stressor for aquatic environments, not only due to their acidity and high metal concentrations, but also because of electrolyte concentrations. Ion-rich mine can disturb the seasonal mixing lake waters, even leading permanent stratification, i.e. meromixis. In this study, we investigated two small natural lakes receiving from closed Ni-Cu mines. To characterize present chemical physical conditions these boreal lakes, collected water samples in-situ column measurements seasonally in 2017 2018. We modelled stability meromixis under varying physico-chemical meteorological with MATLAB-based open-source model code, MyLake. Chemical analyses show that both currently meromictic chemocline separating circulating, well-oxygenated upper non-circulating, hypoxic bottom water. The main anion was SO 4 while cations were Ca, Mg, Na, K. Elevated concentrations conservative elements flowing areas crucial maintaining Modelling scenarios suggest would be sustained several decades if external load ceased completely. Lake morphology sheltered surroundings seem contribute lakes. Consequently, our results indicate headwaters sensitive persistent when loading is mild.