Limnological and geochemical comparisons of two sulphide mine pit lakes

Geochemistry of two abandoned pit lakes, Rävlidmyran and Udden, were studied in northern Sweden. Both lakes show strong similarity with other mining lakes in terms of low pH, high metal and sulphate contents. Still, they have distinctly limnological and geochemical characteristics. The results indicate Rävlidmyran Lake is oligotrophic and meromictic. It is permanently stratified due to vertical density gradients, which strongly controls the vertical elemental distributions. Udden is a dimictic lake. The autumn overturning cause most limnological parameters and chemical components distribute homogeneously. The thermal strata when stratified do not control the elemental distribution. In both lakes, it is found that the scavenging processes by particles are not a significant factor controlling trace metal distributions due to the low suspended particle concentration. Sulphate reduction was not observed, although the oxygen concentration is poor in the deep waters. Thus precluding an important precipitation of trace metals as metal sulphides.