Mining lakes in a disturbed landscape: Application of the EC Water Framework Directive and future management strategies

Some of the several hundred Lusatian mining lakes originating from lignite mining will be among the largest and deepest lakes in Germany. A special problem of many of these lakes is severe acidification. According to the EC Water Framework Directive (WFD), artificial lakes larger than 0.5 km2 have to be monitored and managed in order to establish or maintain a state of so-called good ecological water quality. Therefore the WFD demands the definition of type-specific reference conditions as those of the closest comparable surface water body type in nature, such as natural acidic volcanic crater lakes or oligo- to mesotrophic neutral hard water lakes. We propose a classification scheme for mining lakes applying acidity and planktonic colonization as criteria. Five types of lakes are distinguished ranging from extremely acidic to neutral hard water lakes. Phytoplankton and especially metazoan zooplankton are introduced as intriguing and simple indicators for different states of ecological quality in highly acidic mining lakes. We recommend that extremely and very acidic lakes should remain in the acidic state to protect these as valuable ecosystems, whereas moderately and weakly acidic lakes can be managed by external flooding, chemical or ecotechnological measures to achieve neutral water quality conditions necessary for recreation or fishery use.