Colonization of acidic mining lakes:: Chydorus sphaericus and other Cladocera within a dynamic horizontal pH gradient (pH 3-7) in Lake Senftenberger See (Germany)

Acidic mining lakes are man-made habitats, which differ greatly from natural acidic lakes in their water chemistry. In order to study the potential for colonization of mining lakes by Cladocera we investigated their in situ distributions within a pH gradient from 3 to 7.5 occurring in Lake Senftenberger See (Germany). We found that species in situ pH minima were higher and the overall diversity at the respective pH values was lower in the investigated mining lake in comparison to natural acidic lakes. Possible explanations involve the specific water chemistry in mining lakes. Chydorus sphaericus was the most acid-tolerant species and occurred along the entire pH gradient. We experimentally tested the effect of lake water of different pH values on C. sphaericus. Surprisingly, its survival was the highest at low pH (3-4), while moderately acidic and neutral pH (5-7) had a well-expressed toxic effect on the animals. About 20% of C. sphaericus survived when transferred from pH 3 to pH 7 and vice versa, which suggests that this species is a generalist in relation to pH. As Cladocera display species-specific pH tolerances, we suggest that they could be a useful group for ecological quality assessment of acidified mining lakes.