Aquatic sciences

Lake Huron's food web has experienced drastic changes in response to multiple stressors including declines in offshore productivity, decreased trophic transfer efficiency and a transformation of the benthic food web. However, how these changes have affected the diets and isotopic niches of predatory fish is largely unexplored. My diet study analysed stomach contents from five predatory fish species (lake trout, lake whitefish, chinook salmon, rainbow trout, and walleye) from the Ontario waters of Lake Huron. My isotopic study focused on lake trout and lake whitefish, based on community concerns that recovering lake trout are competing with or consuming lake whitefish. By contrast, I found that lake whitefish were a minimal component of lake trout diets, and the diet and isotopic overlap between these two species was low overall, but varied regionally. Both the dietary and isotope analyses reflect the high regional diversity of energy sources used by predatory fish.

Author Keywords: Food web, Isotopic Niche, Lake Huron, Predator-prey, Regime shift, Regional Energy Sources

Animals are essential to freshwater biogeochemistry and productivity. Through their excretion, aquatic consumers release bioavailable nutrients and carbon that can vary with animal taxonomic rank, trophic position, and abiotic factors such as light and nutrient supply. In fresh waters, light and nutrient supply is often modulated by dissolved organic matter (DOM), a "murky" component in the water that gives it a brown color and that may indirectly affect animal nutrient and carbon excretion. Additionally, contaminants can impact animal physiology, altering metabolism and inducing stress, further affecting nutrient and contaminant excretion. The size and structure of the ecosystem, including community composition and biomass, can also impact the contribution of aquatic animals to the elemental pool. To understand these dynamics, I examined animal‐mediated elemental cycling in freshwater ecosystems across gradients of DOM concentration and composition and under contaminant exposure. I tested fish and invertebrate nitrogen, phosphorus, and DOM excretion across trophic positions during two sampling events in Lake Erie and in naturally DOM-variable streams and lakes. I also investigated the effects of chronic exposure to silver nanoparticles (AgNP) under environmentally relevant conditions on fish nutrient and silver (Ag) release. I found that aquatic animals can be a substantial nutrient contributor to the nutrient pool, particularly when their population biomass is high and ambient nutrient concentrations are low. I also detected nonlinear relationships between animal nutrient excretion and DOM characteristics that varied with taxonomic rank and trophic position and that dampened at larger ecological scales. Importantly, I identified several fish DOM excretion signatures that differed relative to ambient DOM and reported the first fish Ag excretion rates under AgNPs exposure. My results underscore the context-dependency and variability inherent in animal-mediated elemental cycling, highlighting the critical role of animals as both modifiers and conduits of nutrients, DOM, and contaminants in aquatic ecosystems.

Author Keywords: carbon, consumer-nutrient driven dynamics, ecological stoichiometry, nitrogen, phosphorus, silver nanoparticles

My study was primarily focused on the comparison of life history traits between stocked American eel and their naturally recruited conspecifics in Lake Ontario and the upper St. Lawrence River (USLR/LO). I found that stocked eels experienced faster annual growth than their naturally recruited conspecifics and were comprised of a greater proportion of males. These findings indicate that the life history patterns of American eel may be genetically predisposed. Additionally, my study served to characterize the diets of stocked American eel and examine possible associations between eel and prey size. The eels consumed a number of macroinvertebrate prey orders as well as fishes and macrocrustaceans, with the latter prey items being more prevalent in the diets of larger eel specimens. A disparity in eel growth and body condition was observed between two primary stocking locations and were likely attributable to differences in available forage and habitat. Lastly, growth, body condition, and stocked eel diet were compared between lentic and lotic habitats. Eels from lotic streams experienced slower annual growth and had reduced body condition, and their diets were comprised of smaller prey items. The results of this study suggest that the current stocking methods employed in the USLR/LO are not suitable to restore the natural recruitment of individuals that will exhibit desired life history traits.

Brook trout (Salvelinus fontinalis) are declining across Ontario in both numbers and distribution, prompting concern for their future. Here, conventional, emerging, and predictive tools were combined to document brook trout occupation across seasons using streams in Haliburton County, ON as model systems. By using the Ontario Ministry of Natural Resources and Forestry's (OMNRFs) Aquatic Ecosystem Classification (AEC) system variables with environmental DNA (eDNA) sampling and backpack electrofishing, my research supports the development of species occupancy models (SOMs) and eDNA as tools to document brook trout occurrence. To do this, eDNA sampling was validated in Canadian Shield stream environments by comparison with single-pass backpack electrofishing before seasonally sampling two river systems across their main channel and tributaries to assess occupancy. Streams were classified as potential high, moderate, and low-quality brook trout habitats using indicator variables within the AEC and sampled seasonally with eDNA to quantify occupancy and relate it to habitat potential at the county scale. Results showed eDNA to be an effective tool for monitoring fish across Canadian Shield landscapes and that brook trout occupancy varied seasonally within and across watersheds, suggesting that habitat and fish management strategies need to consider seasonal movement and spatial connectivity. Using these tools will enable biologists to efficiently predict and document brook trout occurrences and habitat use across the landscape.

Author Keywords: Aquatic Ecosystem Classification, brook trout, Canadian Shield, connectivity, environmental DNA, seasonal occupation

Recent agricultural land use change in east-central Ontario, including the expansion of intensive agriculture (corn and soybean crops) and tile drainage (TD) infrastructure, may alter the fluxes of both phosphorus (P) and nitrogen (N) to the Lower Great Lakes. Through intensive monitoring of several sub-watersheds that encompassed a range of row crop and TD extents, this study examined differences in stream N and P concentrations both seasonally and during variable flow conditions, to better understand land use/land cover (LULC) relationships with nutrient export. There was no clear relationship between total P (TP; concentration or export) and agricultural LULC, and instead, TP delivery was highly sensitive to flow events, and TP concentrations (especially particulate P; PP) were significantly higher during event flow compared with baseflow. In contrast, the dissolved fraction of P (total dissolved P; TDP) and dissolved nitrogen as nitrate (NO3-N) were not sensitive to flow, but were instead positively related to row crop agriculture, and associations between NO3-N concentrations/export and tile-drained row crop area were particularly strong (concentration r2 = 0.93; export r2 = 0.88). Regression relationships showed that with every 10% increase in row crop area in watersheds, NO3-N and TDP flow-weighted concentrations increased by 0.34 mg/L and 1.5 µg/L, respectively. As well, the same 10% increase in row crop agriculture translated to an increase of NO3-N export of as much as 130 kg/km2. Geospatial records of TD are incomplete in east-central Ontario, which presents challenges for evaluating the contribution of TD to nutrient export. Understanding the response of nutrients to changes in agriculture and agricultural practices is an integral part of watershed management as rapid changes in both urban and agricultural LULC continue to put pressure on water quality in the Lower Great Lakes.

Author Keywords: East-Central Ontario, Nutrient Export, Row crops, Streams, Tile Drainage, Water Quality

Recent declines in growth and condition of Great Lakes' lake whitefish (Coregonus clupeaformis) have been linked to ecosystem-wide changes stemming from the invasion of dreissenid mussels. To test the influence of invasive mussels on this commercially important coregonid species, we collected archived scale samples from ten Great Lake locations and analyzed long-term changes in growth rates, delta 13C and delta 15N stable isotope ratios before and after mussel establishment. There was a decrease in pre-maturation growth after establishment in all four locations where we examined back-calculated growths. In six of the seven locations with dreissenid populations, a significant increase in delta 13C and a significant decrease in delta 15N was found. In dreissenid-absent locations of Lake Superior, we did not see changes in growth or isotope ratios indicative of a major regime shift. Observed shifts in isotopic signatures provide evidence for an increased reliance on nearshore food sources and shallower depth distribution as a result of dreissenids, which likely contributed to lowered growth of lake whitefish.

Author Keywords: Diporeia, Dreissenids, food web, Great Lakes, invasive species, lake whitefish

The purpose of this study was to quantify the variation of baseline carbon and nitrogen stable isotope signatures in the Lake Simcoe watershed and relate that variation to various physicochemical parameters. Particulate organic matter samples from 2009 and 2011 were used as representatives of baseline isotopic values. Temporal data from two offshore lake stations revealed that δ15N of POM was lowest mid-summer and highest after the fall turnover. POM δ13C was variable throughout the summer before declining after fall turnover. Spatial data from the lake and the tributaries revealed that POM stable isotope signatures were highly variable. Various physicochemical parameters indicative of phytoplankton biomass were significantly positively correlated with POM δ15N and significantly negatively correlated with POM δ13C. The correlations were mostly significant in the tributaries, not the lake. Moreover, many of the correlations involving δ15N of POM were driven by extreme values in Cook's Bay and its tributaries. In general, it's likely that different processes or combination of processes were affecting the δ15N and δ13C POM in the Lake Simcoe watershed as physicochemical parameters alone could not explain the variability. Measuring the δ15N of ammonium and nitrate, as well as the δ13C of DIC would help discern the dominant nitrogen and inorganic carbon cycling processes occurring in the Lake Simcoe watershed.

Author Keywords: δ13C, δ15N, isotopic baseline, particulate organic matter, spatial variation, stable isotopes

Due to their effective antibacterial and antifungal properties, silver nanoparticles (AgNPs) have quickly become the most commonly used nanomaterial, with applications in industry, medicine and consumer products. This increased use of AgNPs over the past decade will inevitably result in an elevated release of nanoparticles into the environment, highlighting the importance of assessing the environmental impacts of these nanomaterials on aquatic ecosystems. Although numerous laboratory studies have already reported on the negative effects of AgNPs to freshwater organisms, only a handful of studies have investigated the impacts of environmentally relevant levels of AgNPs on whole communities under natural conditions. This thesis examines the effects of chronic AgNP exposure on natural freshwater littoral microcrustacean, benthic macroinvertebrate and pelagic zooplankton communities. To assess the responses of these communities to AgNPs, I focused on a solely field-based approach, combining a six-week mesocosm study with a three-year whole lake experiment at the IISD – Experimental Lakes Area (Ontario, Canada). Our mesocosm study tested the effects of AgNP concentration (low, medium and high dose), surface coating (citrate- and polyvinylpyrrolidone [PVP]-coated AgNPs), and type of exposure (chronic and pulsed addition) on benthic macroinvertebrates in fine and stony sediments. Relative abundances of metal-tolerant Chironomidae in fine sediments were highest in high dose PVP-AgNP treatments; however, no negative effects of AgNP exposure were seen on biodiversity metrics or overall community structure throughout the study. I observed similar results within the whole lake study that incorporated a long-term addition of low levels of AgNPs to an experimental lake. Mixed-effects models and multivariate methods revealed a decline in all species of the littoral microcrustacean family Chydoridae in the final year of the study within our experimental lake, suggesting that this taxon may be sensitive to AgNP exposure; however, these effects were fairly subtle and were not reflected in the overall composition of littoral communities. No other negative effects of AgNPs were observed on the pelagic zooplankton or benthic macroinvertebrate communities. My results demonstrate that environmentally relevant levels of AgNPs have little impact on natural freshwater microcrustacean and benthic macroinvertebrate communities. Instead, biodiversity metrics and community structure are primarily influenced by seasonal dynamics and nutrient concentrations across both lakes. This thesis highlights the importance of incorporating environmental conditions and the natural variability of communities when examining the potential risks posed by the release of AgNPs into the environment, as simplistic laboratory bioassays may not provide an adequate assessment of the long-term impacts of AgNPs on freshwater systems.

Author Keywords: Benthic macroinvertebrates, IISD - Experimental Lakes Area, Littoral microcrustaceans, Silver nanoparticles, Whole lake experiment, Zooplankton

The main goal of this thesis was to assess the potential impacts of discharges of treated effluent from a small facultative sewage lagoon serving approximately 300 residents of the Mississaugas of the Credit First Nation to freshwater mussel populations in Boston Creek, a small tributary of the lower Grand River. The current resident mussel populations inhabiting Boston Creek were assessed using semi-qualitative visual surveying methods. In addition to various population level observations, other possible point and non-point influences on water quality in Boston Creek were identified. Following this, Lasmigona costata mussels were deployed as biomonitoring organisms alongside passive samplers during the October 2017 lagoon discharge period. Time weighted average (TWA) concentrations of select Contaminants of Emerging Concern (CECs) and Polycyclic Aromatic Hydrocarbons (PAHs) were estimated from levels of these compounds accumulated on passive samplers to understand the influence of wastewater on water quality in Boston Creek. Finally, mussel tissues were analyzed for various biomarkers of exposure to contaminants. Population surveys indicated that Boston Creek supports a plentiful and diverse community of freshwater mussels and may be a refuge for the Species of Special Concern, Villosa iris. Passive sampling revealed that most PAHs measured were present at concentrations below detection limits, while CECs were typically detected at relatively low concentrations (ng/L) directly downstream of the lagoon discharge. Biomarker responses detected in Lasmigona costata generally could not be attributed to exposure to the lagoon effluent but these data may indicate response to other point and non-point sources of pollution that could be affecting resident freshwater mussel populations in Boston Creek. The mussels surveyed in Boston Creek may be displaying community level effects of exposure to other sources of pollution in the area. The results of this thesis will help in establishing water quality guidelines in the lower Grand River watershed that will assist in the recovery strategy for freshwater mussel species at risk in Ontario.

Author Keywords: Biomarkers, Biomonitoring, CECs, First Nations, Freshwater Mussels, SAR

The potential impacts of domestic wastewater (DWW) on the source of drinking water for the M'Chigeeng First Nation were monitored as part of the development of a Source Water Protection plan. During a period of continuous overflow of the Gaaming Wastewater Lagoon serving the community, the chemical tracers, caffeine and sucralose were tracked in West Bay with Passive Organic Chemical Integrative Samplers (POCIS). From the results, we speculated that DWI impacts could have been from three possible DWW sources. POCIS deployed above and below the thermocline indicated a higher mean sucralose concentration of 2.52 ± 1.83 ng/L in the hypolimnion of West Bay relative to mean epilimnetic sucralose concentrations of 0.56 ± 0.02 ng/L, suggesting possible wastewater percolation with an estimated time of travel of 61.5 days. Microbial loads of 200 CFU/100 ml E. coli from the lagoon overflow into Mill Creek decreased to 60 CFU/100 ml before entering West Bay. West Bay's wastewater assimilative capacity met Provincial Water Quality Objectives in the epilimnion and hypolimnion except for dissolved oxygen in the hypolimnion at 4.16 ± 1.86 mg/L, which is a threat to the onset of hypoxia for fish (i.e. <5 mg/L). Assimilative capacity results support a Fall lagoon discharge.

Author Keywords: caffeine, drinking water, Passive Organic Chemical Integrative Samplers (POCIS), sucralose, thermocline, wastewater