Metals in Chironomidae larvae and adults in relation to lake pH and lake oxygen deficiency

Summary

Concentrations of Fe, Mn, AI, Zn, Cu and Cd were measured in chironomid larvae and adults sampled from 3 acid lakes (pH range 4.8–5.3), 2 of which became anaerobic at depth, and 2 circum- neutral lakes (pH = 6.3), 1 which became anaerobic in south-central Ontario, Canada. Larvae from acid, anaerobic lakes contained lower concentrations of Zn and Cu and adults contained lower Zn and Cd vs. those sampled from the 2 non-acid lakes. In contrast, larvae from the acid oxic lake contained the greatest concentrations of Zn and Mn and adults contained greater Zn vs. the 2 non-acid lakes. Concentrations of Fe and A1 in larvae were inversely related to lake pH. Mn and A1 tended to be lower in adult chironomids from the acid lakes, whereas, Fe and Cu of chironomids did not differ among the 5 lakes sampled. Transfer efficiencies showed that 60 to 100 % of Zn, Cu and Cd concentration was transferred from sediments to larvae and to adults. In general, 20–50 % of Fe, A1 and Mn concentration was transferred from sediments to larvae with 10 % of this amount transferred from larvae to adults. Abundances of larvae (# m⁻²) were up to 5 fold greater in 2 of 3 acid lakes vs. non-acid lakes with the Chironomini and Tanytarsini dominanting the chironomid community in the acid lakes. In contrast, the non-acid lakes had a more diverse chironomid communities. Estimates of the mass of metal transferred from lake sediments to winged adults show that the mass that leaves the lake via insect emergence is the same for both acid and non-acid lakes, due to the greater densities of chironomids in acid lakes.