UBC Theses and Dissertations
Assessing midges as paleoecological indicators Dickson, Travis
Three exclusive studies (in-vitro, observational and empirical) comprise this doctorate dissertation aimed at assessing the capacity of midges (Order Diptera: Families Chironomidae, Chaoboridae and Ceratopogonidae) as paleoecological indicators. In-vitro experiments were conducted to determine the impact that temperature and salinity have on midge development and survival. Results indicate that some taxa may achieve optimal development at cooler temperatures; most taxa are cued for emergence by, and require, warmer temperatures; exposure to temperatures that are too warm may result in developmental stress and sometimes death; midge emergence events appear more or less synchronous; and emergences may be controlled by a threshold temperature as opposed to accumulated degree-days. Also, in-vitro experiments were conducted to assess larval midge salinity thresholds (LD50s). Dasyhelea (Ceratopogonidae), Cricotopus/Orthocladius, and Cladotanytarsus mancus type appeared to have the highest salinity LD50s while Chironomus anthracinus type and subtribe Tanytarsina displayed the lowest. In the second study, water chemistry and environmental data were compared with midge assemblage data using multivariate analysis to assess the environmental gradients that limit midge distributions in the Hudson Bay Lowlands (northeastern Manitoba). The results demonstrate the midges’ potential as paleosalinity indicators. The third study involved extracting sediment cores from four separate lakes within the Hudson Bay Lowlands, each extracted from a pond at a different elevation (range from 127 to 10 m above sea level) and distance from the current Hudson Bay shoreline (range from 104 to 2.5 km). My reconstructions suggest that two inland ponds experienced an initial gradual freshening trend from their inception to <1,000 cal. years BP, followed by more recent rapid freshening. Reconstructions for two ponds situated proximal to Hudson Bay indicate stable salinity through the entirety of the sediment records. Quantitative salinity reconstructions for each of the four sampled ponds were ‘statistically insignificant’ (P ≤ 0.05). Predicted isostatic rebound rates, inferred by linear extrapolation of age depth models constructed for four Hudson Bay Lowland ponds, do not indicate an exponentially declining salinity trend as expected.
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