LONG-TERM INVERTEBRATE COMMUNITY RESPONSE TO TOXAPHENE TREATMENT IN 2 LAKES - 50-YR RECORDS RECONSTRUCTED FROM LAKE-SEDIMENTS

Analysis of sediment cores from two toxaphene-treated and one untreated lake basin demonstrates both the short-term effect of toxaphene applied in 1961-62 and the longer term effect of subsequent trout stocking on invertebrates. In Chatwin Lake (higher toxaphene concentration), planktonic cladocerans decreased in abundance, and dominance quickly changed from small- to large-bodied types. Bosmina was reduced by 88% at the time of toxaphene application and was eliminated during the 1970's as invertebrate predators like Chaoborus americanus increased in response to the poor survival of stocked fish. Short-term toxic effects were not detectable in cores from Peanut Lake (lower toxaphene concentration). In both treated lakes, large invertebrates became dominant with the absence of native fish and during trout stocking. Chaoborus spp. remained at low levels throughout the 1960's in both treated lakes compared with the untreated lake, possibly due to residual toxaphene toxicity and/or to predation by stocked fish. Toxicity to total chironomids was not detected, although genera-specific responses were not analysed. While the higher toxaphene dosage caused residual toxicity in Chatwin Lake for at least a decade, the manipulation of fish communities was primarily responsible for long-term changes in the invertebrates of both lakes.