Since 1990, numerous highly acidic hardwater lakes have formed in Lusatia, eastern Germany, after decommissioning of most open-cast lignite mines. With regard to plans for neutralisation and subsequent use of these lakes for fisheries and the risk of reacidification of previously neutralised lakes, there has been an urgent need to determine the lower acceptable pH-limits for indigenous fish species.
In laboratory experiments, embryos and larvae of vendace (Coregonus albula), pike (Esox lucius) and tench (Tinca tinca) were exposed to reconstituted water (pH 3.50–7.40) with the major hydrochemical properties of the post-mining lakes. According to their acid tolerance, the early life stages of the investigated species had the following ranking: vendace (survival only at circumneutral pH) < tench (few survivors at pH 5.50) < pike (survival at pH 5.50 not affected, but growth reduced). High mortalities were generally recorded (1) throughout cleavage phase and early embryonic phase, (2) around hatching, and (3) at the transition to exogenous nutrition. These critical developmental periods as well as the observed effects were similar to those observed in soft, acid water. However, the critical pH-values established in this study tended to be higher than those derived from field observations on reproduction of the respective species in softwater lakes. The deleterious effect of the high Al concentrations in the reconstituted post-mining lake water was apparently greater than the protective effect of the elevated Ca level. When considering the severe effects of reconstituted post-mining lake water on embryos and larvae of pike, tench and especially vendace, maintenance of neutral pH is of critical importance when post-mining lakes are used for fisheries.