Biology - Master's Theses

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Browsing Biology - Master's Theses by Subject "acidification"

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    Modelling trophic recovery, interactions, and food web dynamics across smelter-damaged lakes
    (2023-04-20) Dawson, Jade C.
    Unstable and simplified freshwater food webs threaten the long-term potential of Canadian fisheries due to lack of resiliency in response to stressors including pollutants, climate change, and invasive species. This study utilizes lakes in Sudbury, Ontario to highlight potential drivers and limiting factors of trophic recovery from acidification and heavy-metal pollution from historical nickel smelting emissions. Three lakes across the smelter-impact gradient were selected: one severely damaged lake with a barren watershed (Baby Lake), one severely damaged lake that received sub-watershed liming treatment but retained partial forest cover (Daisy Lake), and one minimally impacted lake with intact forest but had previously been limed to enhance a fish population (Nelson Lake). Two reference lakes far from Sudbury impacts were selected for comparison. Twenty Sudbury region lakes were examined to contextualize fish community assemblages and size data across the smelter deposition zone. Stable isotope ratios of carbon (δ 13C) and nitrogen (δ 15N) were quantified in yellow perch (Perca flavescens), smallmouth bass (Micropterus dolomieu), and baseline organisms to develop quantitative population metrics and describe dietary niche partitioning in each study lake. The barren watershed lake had lowest trophic positioning, smallest body size and niche area, and greatest niche overlap among fish species. The semi-barren and forested watershed lakes were more similar to reference lakes than barren lake in isotopic metrics, signifying significant trophic recovery; however elevated niche overlap revealed additional recovery in these lakes is ongoing. Including stable isotopes in recovering lake studies provides ecosystem insights overlooked by traditional biomonitoring approaches that are critical in understanding freshwater food web responses.
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    Set for success: ecological factors facilitating restoration of self-sustaining Lake Trout (Salvelinus namaycush) populations in acid-damaged lakes
    (2022-05-19) Louste-Fillion, Jasmine
    Sudbury, Ontario, Canada is a site of extreme biodiversity loss due to widespread acidification from over a century of metal mining and smelting. Lake trout (Salvelinus namaycush) were the most widely and severely impacted of the resident sportfish but with massive emission reduction in recent years, their populations have since shown significant signs of recovery. The objective of my study was to identify conditions associated with lake trout recolonization and recruitment by conducting fish and water quality surveys on 31 oncedamaged lakes across Sudbury’s historic acid deposition zone. Lake trout biomass and odds of lake trout recruitment success increased in lakes with more depth of usable lake trout habitat, higher zooplankton biomass and a lower concentration of dissolved organic carbon. A history of hatchery stocking of lake trout was a top predictor of total lake trout biomass in standardized gillnet surveys but did not emerge in top models for predicting natural recruitment or the total biomass of natural lake trout in the lake. These results demonstrate the importance of lake-specific ecological factors in the reestablishment of lake trout populations, regardless of whether the source of the population was hatchery stocking, migration from neighbouring lakes or residual populations that survived acidification. Overall, my study shows evidence that Sudbury’s historically damaged lakes have been extensively recolonized and are no longer limited by acidic conditions. In many cases, they have shifted to simplified fish communities in which zooplankton may be a primary prey source for lake trout. Water chemistry factors, in particular the increase in concentration of dissolved organic carbon and the associated decrease in water clarity also emerged as potential factors shaping lake trout recovery in my study lakes.