Stratification of mining Lake Goitsche during flooding with river water

From May 1999 until 2002, the mine pit Goitsche in Central Germany was filled with river water from the nearby river Mulde to expedite filling and reduce the acid contained in the residual lakes at the base of the pits. The low pH before the flooding originated from acid mine drainage. A continuous inflow over the period of flooding and beyond could be suspected, as monimolimnia of different chemical composition of dissolved substances could establish and persist over the entire observation period at two deep locations of the lake. During summer, a thermal stratification of the water column allowed the neutral river water only to mix into the epilimnion, while the deeper water layers were not directly affected by the incoming waters. Hence a pronounced stratification of pH through the water column and differences between the separate basins could be observed. Winterly deep circulation could remove the vertical gradients of pH, except for the small volumina of the monimolimnia. By the end of year 2002, the entire lake was neutral with the exception of the small volumes of both monimolimnia.