Tolerance of Ceriodaphnia quadrangula and Diaphanosoma brachyurum(Crustacea: Cladocera) to experimental soft water acidification

Abstract

We analysed in how far the decrease of pH, that is part of the ongoing restoration of the softwater Lake Windsborn (conductivity below 30 μS cm−1), may in future influence the occurrence of the two cladoceran species Ceriodaphnia quadrangula and Diaphanosoma brachyurum. In the field, the abundance of Ceriodaphnia was positively correlated with lake water pH, whereas there was no correlation between abundance and pH for D. brachyurum. Experiments on the tolerance against acidification included dynamic (24 h) and static tests (24, 48 h, 30 d), and were conducted with acidified lake water. C. quadrangula tolerated a slight acidification to pH 5.2, but not pH 4.8, whereas the NOEC value seems to be between pH 4.2 and 4.5 for D. brachyurum. Differences between the experimental NOEC values and field data may be explained by diurnal pH fluctuations and the low ion content of Lake Windsborn which puts an additional physiological challenge to its inhabitants.