CHIRONOMIDAE (DIPTERA) RESPONSES TO 2800 YEARS OF CULTURAL INFLUENCE; A PALAEOLIMNOLOGICAL STUDY WITH SPECIAL REFERENCE TO SEDIMENTATION, EUTROPHICATION, AND CONTAMINATION PROCESSES

Abstract

Chironomid fossil assemblages in sediment cores collected from the Bay of Quinte, Lake Ontario, were examined to assess the impact of cultural development on the aquatic environment and to estimate, semi-quantitatively, the relative importance of the various impact processes influencing the chironomid communities. The impact of the six cultures defined in the core—the British–Modern, French, Iroquois, Algonkian, Hopewell, and pre-Hopewell periods—was exerted through eutrophication, sedimentation, and contamination processes. Although the chironomid communities in general followed the accepted theories of faunal response to eutrophication, the impact of sedimentation compounded and at times overshadowed the impact of eutrophication. The chironomid community, which responded to initial European colonization by developing a more eutrophic fauna parallel with increased productivity in the bay, reverted to a more oligotrophic fauna when large scale deforestation of the watershed introduced massive amounts of clay sediments into the bay. The resulting unstable bottom conditions and dilution and/or burial of food materials led to an imbalanced oligotrophic fauna characterized by Micropsectra. This fauna was maintained until the high rates of mineral sediment accumulation declined and the effects of eutrophication became manifest. The transition from the imbalanced oligotrophic fauna to the depleted Chironomus/Procladius fauna tolerant of the present-day eutrophic conditions was so rapid that the intervening mesotrophic Phaenopsectra community was unable to develop fully. The recent increased incidence of deformed larvae implicates industrial and/or agricultural contamination in the continued degradation of the Bay of Quinte fauna.Primitive cultures similarly had measurable effects on the chironomid communities. The “more eutrophic” fauna engendered by the Hopewell culture was not inhibited by the accompanying accumulation of fine sediments as in the European periods and only reverted to a more oligotrophic fauna when reduced populations brought decreased productivity during the Algonkian and early Iroquois stages.