Fossil midge associations and the historical status of fish in acidified lakes |
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| Authors: | M G Johnson J R M Kelso O C McNeil W B Morton |
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| Institution: | (1) Department of Fisheries and Oceans, Canada Centre for Inland Waters, P.O. Box 5050, L7R 4A6 Burlington, Ont., Canada;(2) Department of Fisheries and Oceans, Canal Drive, Ship Canal, Post Office, P6A 1PO Sault Ste. Marie, Ont., Canada;(3) 50 Montana Rd., N1E 3M2 Guelph, Ont., Canada |
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| Abstract: | Chaoborid and chironomid (Diptera) fossils were examined in sediment cores form nine Ontario Precambrian Shield lakes that were fishless in 1979. An abundance of Chaoborus americamus (intolerant of predation by fish) throughout cores from four lakes indicated that they were fishless historically. Occurrence of Chaoborus punctipennis and C. flavicans and absence of C. americanus in cores, except near the surface in two cases, indicated that four other lakes were inhabited by fish historically. One of these was probably periodically fishless as suggested by fluctuations among these Chaoborus species. The ninth lake was not suitable for Chaoborus; only one specimen of C. trivittatus was found in this core. Chironomid fossil associations were substantially different in historically fishless and inhabited lakes. Fishless lakes had chironomids typical of eutrophic conditions indicating that seasonal oxygen depletion likely was inimical to fish. Chironomid associations of oligotrophic waters occurred in lakes historically inhabited by fish. Both good water quality and accessibility were required for long-term habitation by fish. Partial recovery of alkalinity and rise in pH were accompanied by substantial re-invasion by fish in two lakes which had been inhabited historically by fish. Diptera associations provide valuable information on the historical suitability of lakes for fish and the presence/absence of fish in regions where acidification of surface waters has occurred. |
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| Keywords: | paleoecology Chaoboridae Chironomidae fish acidification |
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