Effects of subacute doses of cadmium on pH-stressed Leptophlebia marginata (L.) and Baetis rhodani Pictet (Insecta: Ephemeroptera).

Cd uptake, emergence, survival and locomotory activity at two pH levels were studied in a 27-day experiment with Leptophlebia marginata and in a 19-day experiment with Baetis rhodani. Model ecosystems containing recirculating stream water, patches of sediment and leaves, simulated a natural stream. During the experiments, concentrations of Al, Cd, Fe and Zn increased in the water at pH 5, while conductivity decreased. Cd was taken up by both species at a rate which indicated linear uptake kinetics. No steady state of Cd in the animals was observed. The larvae of B. rhodani contained significantly more Cd than the adults (p<0.001). Uptake of Cd by Baetis rhodani was higher at pH 7 than at pH 5 (p<0.05). The survivial of L. marginata was not influenced by pH and Cd stress, but emergence was significantly reduced (p<0.05). The survival and the emergence of B. rhodani were reduced by low pH and also by Cd addition (p<0.01). At pH 7, Cd had no significant adverse effect on survival. Locomotory activity of Baetis rhodani was reduced by low pH and additionally by Cd stress.