Aquatic Invertebrates from the Smoking Hills, N.W.T.: Effect of pH and Metals on Mortality

Abstract

Experiments were conducted on planktonic crustaceans and insect larvae from acidic and alkaline tundra ponds at the Smoking Hills, N.W.T. to determine their tolerance to low pH and elevated levels of potentially toxic elements, including Al. The crustaceans (Daphnia middendorffiana, Diaptomus arcticus, Lepidurus arcticus, Branchinecta paludosa), which are found only in alkaline ponds, died rapidly below pH 4.5. The insect larvae (Orthocladius consobrinus and Limnephilus pallens) from the same alkaline ponds were able to survive for extended periods at pH 3.5, though they do not occur in acidic waters at the Smoking Hills. The red chironomid (Chironomus riparius) is restricted to acidic ponds although it was able to survive not only at pH 2.8, but also in pond water of pH 8.2.Water from an acidic pond (pH 2.8) was markedly more toxic to crustaceans than water from an alkaline pond (pH 8.2) when both were adjusted to pH 4.5. Elevated concentrations of aluminum may account for this additional toxicity of the acidic pond water. Levels reached 20 mg/L Al, and in experiments with Al, additions to the alkaline waters and to the acidic pond waters, after metal removal, caused toxicity to the crustaceans.The absence of crustaceans from acidic ponds at the Smoking Hills may be due to their extreme sensitivity to low pH. The similarly restricted distribution of certain of the insect larvae, in contrast, cannot be explained this simply. Metal concentrations in acidic ponds impose an added stress. Aluminum was found to be the key additional factor to that of H+ ion concentration.Key words: acidic ponds, tundra ponds, Smoking Hills, bioassays, zooplankton, insect larvae, crustaceans, Daphnia, Diaptomus, Lepidurus, Brachinecta, Chironomus, Orthocladius, Limnephilus, heavy metals, aluminum, calcium, sodium, iron, zinc, nickel