Effect of low pH on the chemical composition of aquatic invertebrates from tundra ponds at the Smoking Hills, N.W.T., Canada

Abstract

Experiments were conducted to compare the relative sensitivity and chemical composition of aquatic invertebrates (insects and crustaceans) exposed to low pH. Test organisms were collected from tundra ponds at the Smoking Hills, N.W.T. One of the ponds was alkaline (pH 8.2), the other was acidified (pH 2.8) as a result of natural SO2 fumigations. Based on mortality rates, crustaceans were considerably more sensitive to low pH than insect larvae. Sensitive species (Crustacea: Daphnia middendorffiana, Diaptomus arcticus, Branchinecta paludosa, Lepidurus arcticus; and Diptera: Orthocladius consobrinus) were unable to maintain high internal levels of Na and Cl. K concentrations were also lower in dead and dying Daphnia but not in the more tolerant Diptera larvae (O. consobrinus and Chironomus riparius). There was a net loss of Ca at low pH, but this did not correlate with mortality. Daphnia middendorffiana recovered following brief exposure to pH4.0. During recovery Na and Cl concentrations returned to their original levels. Acid-exposed Daphnia became infected by pathogenic fungi. No evidence of fungal infection was observed in any of the other treatments. Water chemistry also altered the chemical composition of aquatic invertebrates. All of the crustaceans as well as the trichopteran Limnephilus pallens had lower body Na, Cl, and Ca concentrations in the acidified pond water than in the alkaline pond water adjusted to pH 4.5. Part of this difference in their chemical composition may be due to elevated Al concentrations in the acidified pond water.