A1 Refereed original research article in a scientific journal
Properties and Stability of Mining-Induced Meromixis in Two Small Boreal Lakes in Eastern Finland
Authors: Kehusmaa Karoliina, Kauppila Tommi, Österholm Peter, Juntunen Janne, Saarni Saija
Publisher: SPRINGER HEIDELBERG
Publication year: 2023
Journal: Mine Water and the Environment
Journal name in source: MINE WATER AND THE ENVIRONMENT
Journal acronym: MINE WATER ENVIRON
Number of pages: 16
ISSN: 1025-9112
eISSN: 1616-1068
DOI: https://doi.org/10.1007/s10230-023-00915-9
Web address : https://doi.org/10.1007/s10230-023-00915-9
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/178880326
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 their high electrolyte concentrations. Ion-rich mine waters can disturb the seasonal mixing of lake waters, even leading to permanent stratification, i.e. meromixis. In this study, we investigated two small natural lakes receiving waters from closed Ni-Cu mines. To characterize the present chemical and physical conditions of these two boreal lakes, we collected water samples and in-situ water column measurements seasonally in 2017 and 2018. We modelled the stability of meromixis in the lakes under varying physico-chemical and meteorological conditions with the MATLAB-based open-source model code, MyLake. Chemical analyses and water column measurements show that both lakes are currently meromictic with a chemocline separating the circulating, well-oxygenated upper water from the non-circulating, hypoxic bottom water. The main anion was SO4 in both lakes, while the main cations were Ca, Mg, Na, and K. Elevated concentrations of conservative elements flowing from the mine areas are crucial in maintaining the meromixis. Modelling scenarios suggest that the meromixis would be sustained for several decades even if the external load ceased completely. Lake morphology and sheltered surroundings also seem to contribute to maintaining the meromixis in these lakes. Consequently, our results indicate that small headwaters are sensitive to persistent meromixis even when external loading is mild.
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