Browsing by Author "Wissel, Bjoern"

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Open Access
Analysis of Lakewater Isotopes in the Northern Great Plains: Insights From Long-Term Monitoring and Spatial Surveys
(Faculty of Graduate Studies and Research, University of Regina, 2018-10) Haig, Heather Ann; Leavitt, Peter; Wissel, Bjoern; Simpson, Gavin; Hodder, Kyle; Weger, Harold; Stadnyk, Tricia
General circulation models predict that the precipitation deficit of the Northern Great Plains (NGP) will become more pronounced in the future, and that human adaptation to future climate change will require a greater understanding prairie hydrology in order to maintain freshwater ecosystems. One method for disentangling hydrological complexities is to use stable isotopes of hydrogen and oxygen in water to measure the hydrological properties of lakes, including their water balance. In this thesis, I present a long-term (2003-2016), bi-weekly record of water isotopes during summer to assess the differences between instrumental and isotopic measures of hydrology, and determine the variability in lakewater isotopes at the sub-annual and interannual scales. Insights from this long-term record were then applied to a spatial survey of over 100 lakes to quantify the spatial diversity of hydrologic parameters in lakes of the Canadian NGP and investigate the relationship between catchment characteristics and water balance of individual basins. Overall, lake-specific ratios of evaporation to inflow (E/I, %) from direct measurements (mean (μ) = 15.0%, standard deviation (σ) = 20.7) agreed well with isotopic estimates using headwater basin models (μ = 15.3, σ =7.8). Isotope-instrument agreement was improved (μ =12.6 vs. 6.2%) when basin-specific isotope models that considered local connectivity to upstream water bodies were used in calculations. In my assessment of isotope variability, seasonal variation in water isotope values routinely exceeded that at annual scales and demonstrated rapid changes in water sources within a single season, particularly in systems with water residence times <1 year. Inter-annual variability was regulated mainly by large hydrological events that caused isotopic source waters to become more similar across the Qu’Appelle River watershed. A spatial survey of 100+ prairie lakes revealed that isotopic values of inflow to basins was more similar to that of rainfall (δI, μ = -13.5‰, σ = 2.0) than to snow, and further showed that the flow regimes of most lakes (71%) were categorized as open despite the scarcity of channelized surface inflows. Mean water yield 100.8 mm yr-1 (σ= 181.0) and runoff coefficients 22.1% (σ= 45.9) were elevated relative to average conditions in the region, suggesting that lakes were an important feature capturing water on the prairie landscape. Together, these three studies provided a comprehensive assessment of the hydrological status of lakes in the Canadian NGP, and can be used to inform future research and management projects.
Open Access
Dietary Niche and Foraging Ecology of a Generalist Predator, Double-Crested Cormorant (Phalacrocorax Auritus): Insight Using Stable Isotopes
(Faculty of Graduate Studies and Research, University of Regina, 2012-04) Doucette, Jennifer Lee; Somers, Christopher; Brigham, Mark; Wissel, Bjoern; Fallat, Shaun; Hobson, Keith
The ability of predator populations to expand their ranges and adapt to new environments is often attributed to having a generalist dietary strategy, which is thought to be represented both at the population and individual level. Cormorants (Phalacrocorax spp.) are considered to be opportunistic generalists capable of using a wide variety of aquatic prey. This reputation is partially responsible for the global conflict between piscivorous cormorants and fish harvesters, which is one of the most widespread wildlife management issues in history. Despite the persistent belief that cormorants adversely affect economically important fish populations, relatively little is known about their trophic ecology and habitat use. Stable nitrogen and carbon isotopes are popular tools for studying food webs, and offer a comprehensive assessment of diet, trophic position, and ecological niche when combined with traditional diet analyses. However, the interpretation of isotope data may be confounded by variation in the lipid content of sample tissues. No validated lipid-normalization procedures are currently available for any cormorant species, or any fish-eating birds. As such, I first determined the effect of lipids on the stable carbon and nitrogen isotopes (δ13C and δ15N) values in cormorant tissues, and tested three published lipid-normalization models on stable isotope signatures in double-crested cormorant (P. auritus) muscle and liver tissues. The presence of lipids in cormorant muscle and liver altered the stable isotopes values, indicating corrections were required. However, the effects of lipids in cormorants were unpredictable and thus violated a major assumption of published lipid-normalization models. As a result, lipids must be chemically removed from cormorant muscle and liver tissue. I then examined the diet and trophic position of breeding populations of double-crested cormorants from three different lakes. The results revealed that cormorants generally occupied top-predator positions and relied heavily on pelagic prey in all food webs examined. The isotopic values of cormorants and pelagic predatory fish were sometimes similar, suggesting that dietary overlap is possible. To determine whether cormorants are true dietary generalists I studied double-crested cormorants from breeding colonies spanning three major ecoregions. Analyses of stomach contents revealed that at the population level cormorant diet varied widely by location, likely reflecting local food-web structure. However, within populations individuals were much more specialized than expected. Temporal shifts in δ13C and δ15N values in cormorant tissues with different turnover rates (muscle vs. liver) indicated that foraging varied among populations. The dietary niche occupied by cormorants will affect their interactions with fish, highlighting the importance of understanding their impacts to fish populations both at the population and individual level. Ultimately, my research has shown that cormorants do not consume prey indiscriminately, and instead may have more specific and uniform dietary niche requirements than previously considered. From a management perspective, cormorants should not be assumed to have negative effects on fish in all situations; however, further attention is required to determine the impacts of dietary overlap with sport fish. Ecologically, I have shown that generalist species can be much more consistent and specialized than previously considered. Further, individuals within generalist species may be highly specialized, which will change the overall effects of the population on other species in the food web.
Open Access
Double-Crested Cormorant Feeding in Multiple Lake Environments: Intrinsic Markers Reveal Several Prey Sources and Frequent Site Switching by Breeding Birds
(Faculty of Graduate Studies and Research, University of Regina, 2011-12) Bugajski, Aleksandra; Somers, Christopher; Hall, Britt; Wissel, Bjoern; Wilson, Scott D.
Conflicts between piscivorous cormorants (Phalacrocorax spp.) and humans over fisheries resources occur worldwide. To determine the level of cormorant impacts on fisheries, fish biomass removals are estimated but typically assume only one source of prey near the roost or breeding colony. Cormorants can fly long distances (>30 km) to forage, possibly resulting in fish removal being spread out over several areas within large lakes, or among other bodies of water. I examined the diet and feeding locations of double-crested cormorants (Phalacrocorax auritus; hereafter cormorants) breeding in a multiple lake environment in north-central Saskatchewan, Canada. A majority of their diet was composed of non-sport and non-commercial fish species. Yellow perch (36-196 mm) were a common prey item for cormorants, making up 30-55% of fish biomass consumed, and were therefore used as a model species to determine sources of cormorant prey. Comparison of carbon (δ13C) and nitrogen (δ15N) stable isotopes values in yellow perch collected by cormorants and those from known locations revealed several prey sources (different lakes and areas within lakes) and frequent, large-scale switching of feeding locations on a daily and seasonal basis. These findings were also substantiated by cormorant surveys throughout the study area using transect counts, and examination of flight directions to and from a major breeding colony. Prey from areas well-removed from the breeding colony lake (up to 30 km away) were an important part of cormorant diet, representing 70% of fish fed to nestlings in 2010 during the early chick rearing stage. Cormorants began to feed closer to the breeding colony during the late chick rearing stage. Linear discriminant analysis revealed classification accuracy of known location yellow perch to range from 69% to 86%, suggesting that stable isotopes of carbon and nitrogen performed well as intrinsic markers of fish source in my study area. My research clearly shows that cormorant consumption of fish happens at a variety of locations, negating the value of the traditional approach of estimating biomass removal from the breeding colony lake as the guideline for making fisheries management decisions. Knowing where prey fish come from and estimating relative proportions taken from various sites will refine biomass removal estimates to help managers better understand potential interactions between cormorants and fisheries. In addition, my research shows that cormorants make decisions about foraging and feeding locations that are independent of breeding colony site selection; i.e., they often use sites well removed from the breeding colony. Factors that influence cormorant foraging locations need to be more thoroughly identified to advance our understanding of their ecology, and to aid fisheries management.
Open Access
Effects of spatial variation in benthic phototrophs along a depth gradient on assessments of whole-lake processes
(Wiley, 2021-09-16) Gushulak, Cale A. C.; Haig, Heather A.; Kingsbury, Melanie V.; Wissel, Bjoern; Cumming, Brian F.; Leavitt, Peter R.
1. Phytobenthos are often underrepresented in both limnological and paleolimnological studies but may play key roles in whole-lake production and ecosystem processes including eutrophication, food-web dynamics, and ecosystem state changes. 2. Photosynthetic pigments, stables isotopes, and diatoms were quantified from surface sediments (0-1 cm) collected across a depth transect of a small, DOC-rich, mesotrophic lake in boreal northwestern Ontario to assess spatial variation in phytobenthos abundance and production. 3. Maximal concentrations of siliceous algae and cyanobacteria pigments occurred at ~2–6 m depth, with abundant tychoplanktonic diatoms, depleted sedimentary δ13C C values, and elevated 33 ratios of precursor chlorophyll a to product pheophytin a, all aligning well with the depths of the thermocline, epilimnetic mixing, and maximum light penetration. 4. These patterns demonstrated the presence of three discrete community assemblages, with greatest mass accumulation occurring at intermediate depths where warm illuminated sediments provide habitat for tychoplanktonic diatoms and cyanobacteria between turbulent shallows and cold and dark depths. 5. If widespread among boreal lakes, this tychoplanktonic zone may exert important effects on whole-lake production, carbon sequestration, benthic-pelagic food-web coupling, eutrophication, and ecosystem state change.
Open Access
Impacts of hydrologic management on the eutrophication of shallow lakes in an intensive agricultural landscape (Saskatchewan, Canada)
(Wiley, 2024-05-01) Gushulak, Cale A. C.; Chegoonian, Amir M.; Wolfe, Jared; Gray, Kristen; Stefano, Mezzini; Wissel, Bjoern; Hann, Brenda; Baulch, Helen M.; Finlay, Kerri; Leavitt, Peter R.
1. Hydrologic management of shallow lakes is often undertaken to prevent fluctua- tions in lake level, and to ensure sufficient water volume for economic, domestic, and recreational uses, but there is inconsistent evidence of whether lake-level sta- bilisation through hydrological management promotes or hinders eutrophication. 2. Here we used multi-proxy paleolimnological assessments of water quality (sedi- mentary carbon, nitrogen, total phosphorus, fossil pigments), and zooplankton community ecology (fossil Cladocera assemblages), combined with Landsat- derived estimates of lake surface area in two shallow eutrophic lakes, in the Prairies of southern Saskatchewan, Canada, to quantify how 8 decades of con- trasting hydrological management strategies (continuous or intermittent) affect primary production and phytoplankton composition. 3. Analysis revealed that irregular hydrological management of Pelican Lake led to sharp increases in primary production concomitant with lake-level decline. In contrast, continuously managed Buffalo Pound Lake, a drinking water reservoir for regional cities, exhibited slow, persistent eutrophication over decades despite active regulation of water levels. In both lakes, strong correlations of δ 15N val- ues with pigments from diazotrophic cyanobacteria (canthaxanthin) showed that N2-fixation increased during eutrophication irrespective of the timing of change. Finally, variation in fossil cladoceran density and composition reflected changes in pelagic and littoral habitats (e.g., reduced macrophyte cover) due to changes in both lake level and water quality. 4. Basin comparison shows that while hydrologic management can moderate water quality degradation due to lake-level change, it does not prevent eutrophication when nutrient influx remains high. 5. Given that regional water availability is forecast to decline in coming decades, we anticipate that continued hydrological management will be unavoidable and will be unable to improve water quality unless nutrient influx is also controlled.
Open Access
Oligotrophication of downwind boreal lakes caused by oil sands-derived enhanced nutrient deposition
(Faculty of Graduate Studies and Research, University of Regina, 2016-12) Wolfe, Jared Daniel; Wissel, Bjoern; Leavitt, Peter; Finlay, Kerri; Simpson, Gavin
Development of the Athabasca Oil Sands Region (AOSR) in northern Alberta, Canada has resulted in the substantial release of emissions, such as reactive nitrogen (Nr) species and base cations, which can fertilize downwind lakes in the boreal forest of Saskatchewan. However, to address the potential impacts of nutrient deposition on these algal communities, interpretations must occur in the context of ongoing regional climate change. Here, I use a factorial paleolimnological analysis to isolate the unique effects of AOSR emissions and climate change on lake geochemistry (C and N stable isotopes and elemental content) and algal assemblages (fossil pigments) over the past ~100 years. Surveyed lakes were either nitrogen (N)- or phosphorus (P)-limited and were located either within an impacted area receiving enhanced AOSR-derived deposition or within an unaffected reference region. Common trends from generalized additive models indicated that all algal groups declined after 1980 in P-limited lakes receiving deposition, coinciding with industrial intensification of the AOSR. In contrast, total algal abundance (as β-carotene and declining C/N ratios) as well as abundances of mixotrophic cryptophytes (alloxanthin) and unicellular cyanobacteria (echinenone, but not canthaxanthin) increased regionally in reference and impacted, N-limited lakes since the mid-1900s. Biomarkers from obligate autotrophs, and sedimentary δ13C and δ15N values, changed asynchronously among lakes, reiterating a fundamental restructuring of the algal community. These patterns suggest that regional climate change has intensified primary production in Saskatchewan boreal lakes and increased cyanobacteria and mixotrophic phytoplankton abundance. However, oligotrophication of impacted, P-limited sites suggests a change in nutrient export from the catchment. Specifically, increased terrestrial vegetation growth due to enhanced nutrient deposition likely resulted in subsequent diminishing of P export to these lakes. This study provides the first evidence of detrimental effects of industrial development on remote downwind lakes. Moreover, I outline a potential mechanism that incorporates a holistic view of how unique effects of the AOSR and climate change have influenced algal community composition over the last century in boreal SK. Careful evaluation of the current and future AOSR industrial footprint is required to fully understand the ramifications of development on Canada’s economy and environment.
Open Access
Potential Impacts of Zebra Mussel Invasion on Gamefish Health and Prey Availability in Prairie Lakes
(Faculty of Graduate Studies and Research, University of Regina, 2022-03-30) Ofosu, Caroline Barbara; Wissel, Bjoern; Somers, Christopher; Brigham, Mark; Hansen, Gretchen
Invasive species are a threat to global aquatic ecosystems. Nonetheless, their impacts can be heterogeneous across systems. Recent reports suggest Saskatchewan (SK) prairie lakes are highly prone to zebra and quagga mussels (ZQM) given their proximity to invasive corridors of Manitoba and three US states (Montana, North Dakota, and Minnesota) where they have been reported. As the effect of ZQM on native species is variable and context-dependent across locations and time, an understanding of prevailing biological, physical and chemical conditions supporting various cohorts of fish communities is necessary for prioritizing mitigation efforts to address the potential effects of these dreissenids in uninvaded systems. To gain these important insights, I investigated diet composition and body conditions of three ecologically and recreationally important gamefishes; walleye (Sander vitreus), northern pike (Esox lucius), and yellow perch (Perca flavescens) sampled from 18 SK prairie lakes. In addition, I assessed the impact of fish size and environmental variables on gamefish body conditions. Twenty-three prey taxa were found in the diets of these fishes. While both invertebrates (amphipods) and fish formed significant constituents of walleye diets, pike concentrated more on fish prey, whereas perch relied more on invertebrates (chironomids and amphipods). Zooplankton was only a minor contributor to the diets of all three gamefish species. Body conditions of walleye and pike decreased with size, but yellow perch populations were in consistently good condition across all size groups. These results suggest preferred fish prey of larger piscivores (i.e., pike and walleye) may be present in insufficient quantity. Lake productivity and alkalinity influenced body conditions of large-sized walleye and yellow perch. The scarcity of pelagic zooplankton prey in the diets of small-sized gamefishes implies these populations may be less threatened by future ZQM invasion than previously assumed. Next, I contrasted stomach content data and Carbon (C), Nitrogen (N), with Sulfur (S) stable isotope analyses to better quantify the relative importance of various foraging habitats to the three gamefish species. Bayesian Mixing models predicted that in about 70% of our study lakes > 55% of gamefish diets were sourced from the littoral region, whereas in ~30% of surveyed lakes, > 55% of gamefishes diets was sourced from the pelagic habitat. General evidence of similar reliance on sediment S sources in lakes where two species co-occurred (walleye and pike or walleye and perch) was observed. Overall, the three predominant gamefishes exhibited comparable dependence on the three feeding habitats (littoral, pelagic, sediment) across SK prairie lakes. Findings of stomach content analysis (SCA) and stable isotope analysis (SIA) were assessed to determine how the two techniques corroborate, contradict or complement each other. Results indicated a lack of correspondence between the two methods utilized in examining walleye diets, suggesting the need to use both techniques as complements for more robust results. Finally, because future invasion by ZQM is expected to significantly impact energy sources of gamefishes, I examined the current environmental controls of reliance on pelagic, littoral, and sediment-based diets. Walleye reliance on pelagic energy sources increased with the maximum depth of lakes and decreased with total dissolved solids (TDS) concentrations, implying the contribution of pelagic diets increase for fish populations in deeper and less saline lakes. However, sediment-based diets were not influenced by any of the selected environmental parameters. Integrating SCA and SIA overall helped to advance our understanding of feeding habits of gamefish populations in SK prairie lakes and demonstrates the value of combining these analyses for a comprehensive understanding of feeding interactions within aquatic ecosystems.
Open Access
Quantifying Human and Ecological Dimensions to Advance Holistic Understanding of Prairie Lake Ecosystems
(Faculty of Graduate Studies and Research, University of Regina, 2018-05) Nanayakkara, Lushani Chaya; Wissel, Bjoern; Leavitt, Peter; Weger, Harold; Stavrinides, John; Diaz, Harry; Rusak, James A
Successfully managing the impacts of changing environmental conditions on complex socio-ecological systems (SES) requires identifying, quantifying, and understanding the multitude of threats facing such systems. Research that transcends disciplinary boundaries is the best means of accomplishing this task. Therefore, in this study, I combined multiple methods from the social sciences and natural sciences to quantify the human and ecological dimensions of prairie lakes in Saskatchewan, Canada. Firstly, to advance understanding of lake-use patterns and users’ perceptions of these systems, I designed and distributed a stakeholder survey. Results indicate primary lakeuses in this region are recreational, particularly fishing. Walleye (Sander vitreus) are targeted more than native fishes such as northern pike (Esox lucius) or yellow perch (Perca flavscens). Overall, respondents expressed concerns about pollution and urbanization, but invasive species and climate change were of minimal concern. Next, I quantified the current status and potential resilience of the aforementioned game fish species to changing environmental conditions using three parameters. I used Bayesian mixing models (MixSIAR) to evaluate resource-use, while body condition was expressed as relative weight indices (Wr), and parasite loads were enumerated via gut analyses. Based on the results, stocked walleye appear to be less resilient to environmental variability compared to naturally occurring species. This suggests that walleye will need to be continuously stocked in the future, particularly under climate change scenarios. Finally, because invasive species are expected to significantly impact game fish populations in temperate regions, and humans being key vectors in the spread and ii establishment of invasive species, I examined stakeholder knowledge about aquatic invasive species (AIS). Results from a survey questionnaire indicated low education and communication success, as respondents exhibited substantial knowledge gaps regarding non-native mussels and key preventative behaviours. Furthermore, I identified correlates of AIS knowledge and recommend exploitation of these predictors to improve effectiveness of education, outreach, and communication efforts. Based on the collated results from this interdisciplinary study, I recommend development of management strategies that focus on ensuring the long-term sustainability of recreational angling, improving AIS knowledge through re-structured education campaigns, and enhancing efforts for detecting AIS transfer. Overall, utilizing an interdisciplinary approach to examine the human and ecosystem dimensions of prairie lakes advanced comprehensive understanding of these complex SES.
Open Access
Resource Use and Ecological Population Structure of Lake Whitefish (Coregonus clupeaformis) Spawning Aggregations in Lake Huron
(Faculty of Graduate Studies and Research, University of Regina, 2015-12) Eberts, Rebecca Lena; Somers, Christopher; Manzon, Richard; Wissel, Bjoern
Lake Whitefish are a commercially and ecologically valuable freshwater species in Lake Huron. Recent environmental changes have had broad impacts on current populations, which threaten the sustainability of this fishery. To properly conserve this resource, multiple sub-populations in the lake must be adequately represented in management regimes. Of special importance are adult spawning aggregations, which collectively contribute to the productivity of the fishery. However, spawning aggregations in Lake Huron are perceived to represent multiple stocks, adding complexity to fisheries management. The current population structure for adult Lake Whitefish is not well understood at the lake wide scale, and previous assessments have primarily used only evolutionary markers (e.g., genetic and phenotypic markers). A shorter-term, food web based marker would be beneficial for understanding the current population structure of spawning aggregations based on ecological relationships. Stable isotopes are integrated food web tracers that encompass patterns in consumer resource use (i.e., prey, location, habitat). In this study, I used δ13C and δ15N stable isotope analysis to compare prespawning resource use by 32 spawning aggregations spanning most of Lake Huron. I found large isotopic variation across aggregations (ranges: δ13C = 10.2 ‰, δ15N = 5.5 ‰), and spatial heterogeneity in resource use identity and diversity (SEAC = 1.02 – 4.27‰2), indicating that aggregations in different lake areas used more local food webs. I used the isotopic structure of the population to classify individuals into 1 of 4 isotopically distinct clusters. Aggregations were composed of individuals from multiple clusters, indicating highly mixed populations. Aggregations in the Main Basin were particularly mixed (3+ clusters), while those in the North Channel and Georgian Bay represented fewer, and different clusters. To aid interpretation of isotopic structure I investigated factors of location, diet, sampling date, fish sex, and fish size as potential mechanisms of isotopic structuring. Analyses of summer fish and prey baseline variation across lake areas indicate locational feeding patterns are likely the primary mechanism driving ecological structuring. For example, δ13C values of summer assemblages explained 82% of the variation in spawning aggregations at overlapping locations. Lastly, to present an overall view of ecological population structure, I grouped spawning aggregations according to like compositions. To this end, spawning aggregations were divided into 6 putative ecological sub populations that reflect regions of local resource use in the lake. Comparison to the current management scheme suggests that current management units are too small and numerous to reflect the ecology of Lake Whitefish. Stable isotopes provided a powerful approach for identifying ecologically based population structure and composition in an inter-mixed freshwater fishery.
Open Access
Responses of Fish and Zooplankton to Climate Variation on the Prairies, and Their Sensitivity to Climate Change
(Faculty of Graduate Studies and Research, University of Regina, 2012-12) Starks, Elizabeth Raye; Wissel, Bjoern; Leavitt, Peter R.; Somers, Christopher; Hudson, Jeff
Climate change is anticipated to significantly increase temperatures and alter current rainfall patterns, which will have important ramifications for aquatic habitats and their biological communities. Current observations indicate that climate effects will vary depending on region and lake type, and some lacustrine areas, such as the Great Plains, are particularly sensitive to these effects. Variations in local climate and lake morphometry create different habitats, which each have unique environmental controls. The anticipated impacts of climate change on aquatic biota can be difficult to evaluate because of potentially contrasting effects of temperature and hydrology on lake ecosystems, particularly in closed-basin lakes within semi-arid regions. To address these challenges, I quantified decade-scale changes in chemical and biological properties of 20 endorheic lakes in central North America in response to a pronounced transition from a drought to a pluvial period during the early 21st century. Lakes exhibited marked changes in chemical characteristics and formed two discrete clusters corresponding to periods of substantially differing effective moisture (as per Palmer Drought Severity Index, PDSI). Discriminant function analysis (DFA) explained 90% of variability in fish assemblage composition and showed that fish communities were predicted best by environmental conditions during the arid interval (PDSI < -2). DFA also predicted that lakes could support more fish species during pluvial periods, but their realized occurrences may be limited by periodic stress due to recurrent droughts and physical barriers to colonization. Zooplankton taxonomic compositions in fishless lakes were resilient to short-term changes in meteorological conditions, and did not vary between drought and deluge periods. Conversely, zooplankton taxa that were exposed to fish decreased substantially in biomass during the wet interval, likely due to increased zooplanktivory by fish. Based on my results, climate change is expected to alter fish species distributions, but it is less clear to what extent non-lethal environmental effects will influence physical health of populations in fish-habitable lakes. To address this question, I investigated the environmental controls of body condition and parasite load in walleye (Sander vitreus), northern pike (Esox lucius) and yellow perch (Perca flavescens) in seven lakes from the prior study. Over a two-year observation period (2009 vs. 2010), I observed large differences in the number of days within the favorable temperature range for ambient fish species. Surprisingly, environmental variables such as lake morphometry and nutrient levels had little relevance, despite their importance in previous studies conducted in boreal lakes. Instead, temperature and salinity were important correlates of fish health. In regard to species-specific effects, walleye was most sensitive to interannual temperature differences, as well as salinity, while yellow perch and northern pike exhibited temperature sensitivity to a lesser degree. Apparently, temperature increases are of particular concern in prairie lakes, as their polymictic nature deprives fishes of a hypolimnetic thermal refuge. Together these findings suggest that semi-arid lakes provide a useful model system for anticipating the effects of global climate change on aquatic communities in closed-basin lakes of semi-arid regions. The particular importance of temperature and salinity indicates that the interaction of global climate change and local hydrology may have particularly detrimental effects not only on the health but also the survival of established fish populations of the Great Plains.
Open Access
Spatial and Temporal Assessments of Zooplankton Community and Stable Isotope Indicators: Developing A Predictive Understanding of Ecological Dynamics In Boreal Lakes
(Faculty of Graduate Studies and Research, University of Regina, 2019-02) Mohamed Usoof, Mohamed Anas; Wissel, Bjoern; Simpson, Gavin; Leavitt, Peter; Scott, Kenneth; Fitzpatrick, Dennis; Vinebrooke, Rolf
Developing a predictive understanding of processes that regulate lake ecosystem dynamics is crucial in the face of environmental perturbations affecting boreal western Canada, particularly atmospheric pollutant deposition from oil sands operations in Alberta and climate change. Based on spatial and temporal analyses of zooplankton communities and their δ13C and δ15N values, my research sought to 1) assess the biological responses to climate and industrial deposition and 2) develop a holistic understanding of regulatory processes of these indicator dynamics to better assess future impacts. First, a spatial assessment of 97 lakes detected significant correlations of zooplankton community composition to environmental gradients vulnerable to industrial deposition, together with intriguing spatial patterns. Yet, unraveling industrial impacts from natural variability was precluded by lack of regional baselines. The effects of both environmental gradients and dispersal on species composition were scale-dependent, emphasizing the need for explicit consideration of spatial scale in regional bioassessments. Second, a multi-lake paleolimnological study revealed that trajectories of zooplankton community compositional turnover during the past century were largely asynchronous among lakes, indicating dominant local effects over climatic forcing. This cautions against regional extrapolation of site-specific results, highlighting the need for intensive replication in regional bioassessments. Specific changes in trajectories corresponding to intensified oil sands development were not detected, suggesting minimal industrial impacts. Third, evaluation of spatial patterns in δ13C and δ15N of taxon-specific zooplankton from a 233-lake survey revealed that relative effects of lake/catchment-specific factors (water chemistry, hydromorphology and land cover) on stable isotope (SI) variation were more important than potential regional factors (lithology, atmospheric nitrogen deposition). The relative importance of specific lake/catchment-specific predictors of δ13C varied among taxa, likely due to contrasting dietary niches and resulting differences in allochthony. This suggests δ13C may respond taxon-specific to limnological changes. Fourth, analyses of δ13C and δ15N time series of taxon-specific zooplankton subfossils during the 20th century demonstrated that they can better reflect environmental impacts on carbon/nutrient fluxes and trophic dynamics in different lake habitats compared to bulk sediment. Beyond indicating limited current biological impacts of industrial deposition and establishing crucial regional baselines, my research provided a comprehensive understanding of regulatory processes of zooplankton communities and SI dynamics, with broad ecological implications for developing indicator frameworks to assess future environmental perturbations in boreal regions.
Open Access
Winter Ecology and Ecophysiology of Prairie-Living Big Brown Bats (Eptesicus Fuscus)
(Faculty of Graduate Studies and Research, University of Regina, 2017-03) Baerwald, Brandon Jeremiah; Brigham, Mark; Wissel, Bjoern; Somers, Christopher; Candow, Darren; Buck, Loren
Hibernation allows animals to survive lengthy periods of energetic deficit, but is not without costs. Hypometabolism, low body-temperature, and inactivity are associated with a variety of costs such as immuno-incompetence, dehydration, and build up of harmful metabolites. Additionally, conditions within hibernacula have a profound influence on hibernation patterns and survival. Periodic arousals and site selection are thought to mitigate these costs, and often involve timing arousals to foraging opportunities and overwintering in locations with stable temperatures and high humidity. I studied prairie-living big brown bats (Eptesicus fuscus) that overwinter in rock crevices and take flight outside of the hibernacula despite a lack of foraging opportunity. My goal was to describe their winter ecology and behaviour, and investigate reasons for winter flight. I found that E. fuscus in my study area use relatively dry hibernacula compared to known cavernous sites and show fidelity to sites between and within years. I found that temperature and wind are important predictors of winter flight, and that arousals remain under diurnal influence. My data suggest that individuals from this particular population spend the majority of their winter energy-stores during steady-state torpor and have mechanisms to decrease evaporative water loss during hibernation. I found typical levels of dehydration as winter progressed and my data indicate no use by bats of a supplemental water source. My research elucidates novel behaviours and traits of this population of E. fuscus, and reduces the paucity of knowledge about winter bat-ecology in the prairies.