The effects of decreasing heavy metal concentrations on the biota of Buttle Lake, Vancouver Island, British Columbia

Abstract

Since 1966, a copper-lead-zinc mine operated by Westmin Resources Limited has been a source of heavy metal input into Buttle lake. Metal levels increased in the lake, peaking in 1980/1981; thereafter improved treatment and collection systems at the mine site have resulted in steadily decreasing metal levels throughout the lake system. The increase in metal concentrations in the lake water was accompanied by increased metal concentrations in salmonid muscle and liver tissues, by elevated levels of hepatic metallothionein and by declines in both species diversity and population for phytoplankton, periphyton and zooplankton. However, recovery of the biota of Buttle lake with decrease in metal concentrations has not followed a simple reversal of the earlier trends. While metal levels in rainbow trout muscle tissue have improved significantly, copper and cadmium liver tissue levels remain significantly higher than for the control lakes. Hepatic metallothionein levels in rainbow trout have declined steadily from a maximum of 269 ± 23 nmol/g in 1981 to a low of 64 ± 22 nmol/g in 1985, which is similar to the control lake. Interspecies comparison of muscle and liver tissue levels both for Buttle lake and for uncontaminated British Columbia lakes found that rainbow trout ( Oncorhynchus mykiss), cutthroat trout ( Oncorhynchus clarki) and Dolly Varden char ( Salvelinus malma) respond differently to metals in the environment. It is apparent that trends in rainbow trout data should not be generalized to include all three groups. As metal concentrations decreased, the phytoplankton community began to change so that beginning in 1983 and continuing well into 1985, a continuous phytoplankton bloom consisting of a virtual monoculture of Rhizosolenia eriensis was present throughout the lake. Accompanying the bloom was a scarcity of zooplankton. However, as levels of R. eriensis peaked in 1985, zooplankton and phytoplankton diversity and species number are improving as previously dominant species begin to reappear.