REMOBILIZATION AND EXPORT OF CADMIUM FROM LAKE-SEDIMENTS BY EMERGING INSECTS

Emerging insects including, Diptera, Odonata, Ephemeroptera, and Trich optera were collected from Lake 382 (L382) in 1991 and 1992 to estimat e quantitatively the export of Cd by aquatic insects from a natural sy stem having elevated Cd concentrations in the water and sediment. L382 is a Canadian Shield lake, located within the Experimental Lakes Area in northwestern Ontario, that received experimental additions of Cd f rom 1987 to 1992. Emerging Diptera (mostly Chironomidae), Odonata, and Ephemeroptera had mean Cd concentrations of 1.41, 0.11, and 0.30 mu g /g wet weight, respectively. An estimated 1.32 to 3.90 g of Cd per yea r were exported from the sediments of L382 depending on the estimate o f production rates used for these groups of insects. Approximately 0.0 5 to 0.17% of the whole-lake Cd load in L382 sediments was exported an nually or 0.12 to 0.39% of the epilimnion Cd sediment load. Insect eme rgence may have resulted in greater Cd export from L382 relative to lo sses via the outflow. Cadmium exported from the sediments by insects m ay be remobilized and become more available to aquatic organisms or en ter the terrestrial ecosystem and become available to insectivores.