| Summary: | Due to the increasing number of acidic mining-pit lakes and a growing awareness of the environmental risks associated with them, pit lakes have attracted more and more attention. This study started with a full-year- round investigation of two abandoned sulphide mine pit lakes, the Rävlidmyran and Udden pit lakes in northern Sweden, followed by studies of two full-scale remediation treatments, liming and sewage sludge treatment, respectively, in the Rävlidmyran pit lake. The aim of this study is to understand the geochemistry of pit lakes and the factors influencing pit lake water quality. Based on this knowledge, effects of different remediation methods are investigated and possible improvement of these methods is explored. Furthermore, the possibility of manipulating the pit lakes to obtain efficient metal attenuation is also explored in this study. The results showed that these two pit lakes have some common characteristics; they have low pH, they are oligotrophic and have high metal and sulphate contents. However, they have developed distinctly different limnology and geochemistry. Rävlidmyran is a meromictic lake, which has a rather stable stratification due to more saline groundwater inflow at depth. Three layers have been developed: the mixolimnion at the top, in which the water is well mixed and saturated with oxygen; the monimolimnion in the deeper lake, which is poor in oxygen and which does not mix with upper water; and the chemocline, which separates the upper and deeper water. The distribution of elements such as Ca, Mg, Na, K, S, Mn, Fe and Zn is seen to be strongly controlled by the stratification with lower concentrations in the upper layer and higher concentrations in the deeper water. The Udden pit lake is a dimictic lake without permanent stratification; only seasonal thermal strata develop. The water is well mixed, which results in rather uniform distribution of parameters such as pH, dissolved oxygen, conductivity and elemental concentrations. It is concluded that a careful characterization ...
|
|---|