Stewart Emily M 201801 Phd.Pdf
THE ROLE OF CHIRONOMIDS AS PALEOECOLOGICAL INDICATORS OF EUTROPHICATION IN SHALLOW LAKES ACROSS A BROAD LATITUDINAL GRADIENT by Emily Meaghan Stewart A thesis submitted to the Department of Biology In conformity with the requirements for the degree of Doctor of Philosophy Queen’s University Kingston, Ontario, Canada (January, 2018) Copyright © Emily Meaghan Stewart, 2018 Abstract The aquatic larvae of chironomids (Diptera, Chironomidae) were historically classified according to lake trophic status, and taxa classified as “eutrophic” were labeled as such because of adaptations for surviving hypoxic or anoxic conditions in the hypolimnion of stratified eutrophic lakes. As such, sedimentary chironomid assemblages have been used to reconstruct production-related variables (nutrients, chlorophyll-a), though this has been problematic, especially in shallow systems, because the response of chironomids to eutrophication is mediated through secondary environmental gradients including oxygen concentration, habitat, and food quality/quantity. In this thesis, eutrophic sewage ponds in the Canadian High Arctic were used to demonstrate that oxygen, not nutrients, is the primary control of chironomid species assemblages. The ability to explicitly test the influence of oxygen versus nutrients on chironomid distributions was made possible by the 24-hr daylight (continuous photosynthesis) and shallow, wind-mixed water column that resulted in oxygen concentrations that were decoupled from the effects of elevated nutrients and production. The subfossil chironomid assemblages were complacent during historical eutrophication, in contrast to marked changes in diatom assemblages, which have a direct physiological relationship with nutrients. Similarly, in shallow eutrophic ponds on islands in Lake Ontario, chironomid assemblages did not appear to be governed by the large gradient in total phosphorus due to the presence or absence of waterbird nesting colonies, but rather by habitat and possible bird- mediated heavy metal pollution.
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