Biogeochemistry

DNAJC5, an HSP40 member, supports synaptic vesicle release and protein folding byactivating HSP70 ATPase activity. In humans, it localizes to presynaptic terminals and endomembrane compartments that are involved in protein trafficking. Mutations in DNAJC5 cause CLN4 disease, a rare adult-onset Batten disease. Dictyostelium discoideum, a model for neurodegenerative research, encodes a putative homolog of DNAJC5, Dnajc5 (DDB0306688), which remains uncharacterized. This study examined Dnajc5 localization and function in D. discodieum. Dnajc5 localized to the endoplasmic reticulum, cytoplasm and nucleolus under both growth and starvation conditions, suggesting a role in proteostasis. Unlike human DNAJC5, Dnajc5 was absent from endomembrane compartments and extracellularly during starvation. Protein quantification revealed increased levels during early development, peaking at the mound stage, and declining thereafter—paralleling gene expression. Immunoprecipitation of Dnajc5 showed no serine phosphorylation or ubiquitination, unlike human DNAJC5. These findings suggest functional differences despite a possible common role in proteostasis.

Author Keywords: actinomycin- D, CLN4, Dictyostelium discoiduem, DNAJC5, Immunoprecipitation, multicellular development

The Wabigoon River is known for an historic mercury (Hg) pollution source, caused by a chlor-alkali facility operating in the 1960s. As legacy Hg contamination continues to cause serious adverse health effects to the local communities living in the Wabigoon River region, it is imperative to undertake additional research to understand the deposition and transport of historical mercury in this system and more importantly, its conversion into methylmercury (MMHg) which renders it bioavailable for ongoing bioaccumulation. The aim of this dissertation was to evaluate the transport and accumulation of Hg species by doing a spatial and temporal analysis of concentrations of mercury and methylmercury along the Wabigoon River, as well as assessing rates of methylation and demethylation, identifying areas of higher methylmercury production. Results show that locations downstream from the pollution source still show elevated mercury concentrations, with levels at least five times higher in water and up to 134 times higher in sediments compared to background levels. Among selected study sites, the Hydroelectric dam, the Wabigoon Rapids wetland and Clay Lake were identified to have high capacity for methylmercury production in the system, with notably Clay Lake presenting a higher potential for methylmercury accumulation due to the observed lower methylmercury demethylation rate. Furthermore, the impact of wetting and drying cycles on Hg methylation in riverbed and wetland locations within the Wabigoon River system was investigated through a laboratory simulation. Findings indicated increased susceptibility of riverbed locations to wetting and drying cycles.

Author Keywords: Demethylation, Mercury, Methylation, Methylmercury, Wabigoon River

A meta-analysis revealed that while there is often a greater degree of contamination of soils and sediments with metals, contamination by mercury (Hg) is a large concern owing to its toxicity at low concentrations. The case study in Guyana characterized Hg and concentrations of other metals (As, Cd, Co, Cu, Mn, Ni, Pb, and Zn) in soil and sediment within gold mined areas. Metal concentrations were low in soil and sediment of sampled gold mines, while the concentrations of Hg were much higher in soil and sediment and contamination was not localized to the mine site. Moss bags and Hg passive air samplers (MerPAS) were deployed to measure atmospheric Hg around a gold mine in Mahdia, Guyana over a 90-day period as well as a 2-day period that encompassed a periodic burn (typically 2-hr). Mercury in moss and MerPAS were positively correlated over both deployment periods, but Hg concentrations measured during the 2-day event were several-fold higher in both moss and MerPAS compared with the 90-day exposure demonstrating that most of the Hg sorbed to both moss and passive samplers is lost during periods of inactivity. Using the 2-day deployment as a conservative estimate of atmospheric Hg exposure, Hg air concentrations around the burning station exceeded 100,000 ng m-3 averaged over a 48-hr period, and moss Hg concentrations were greater than 250,000 ng g-1 around the burning station, although Hg concentrations in both media decreased rapidly with distance. Mercury concentration in soil and sediment was strongly related to organic matter content, which tended to be higher away from the mine site. These controls of organic matter (carbon; C) cycling on Hg distribution and movement are clear at sites exposed to high atmospheric Hg and exist at the global scale, although Hg:C ratios in environmental media are greatly elevated at the gold mine site compared with the global average. Locally sourced biochar did not sufficiently improve physical properties (porosity) in overburden soil, which showed the worse plant response, possibly due to the high clay content that contributes to the "baked" condition of these soils and restrict root growth.

Author Keywords: Biochar, Environmental contamination, Gold mining, Mercury, Metals, Organic matter

Increasing wildfire frequency, driven by climate change, can change the concentration andcomposition of dissolved organic matter (DOM) exported from land into receiving waters by removing terrestrial vegetation, changing soil hydrology, and interrupting microbial degradation. In this thesis, I tested how wildfire impacts the molecular composition and reactivity of DOM. I compared DOM from boreal headwater streams in northwestern Ontario, Canada between 10 catchments recently affected and 10 comparable catchments that were undisturbed for at least 20 years. Using optical spectroscopy, ultra-high-resolution mass spectrometry, and incubation experiments, I found that burned streams had 29% higher average DOM concentrations and contained less bioavailable DOM, which resulted in microbes respiring more CO2 in burned streams rather than using carbon to build biomass. These results indicate that the impacts of wildfire on carbon sequestration have been underestimated and highlight the need to consider wildfire in forest carbon budgets.

Author Keywords: boreal forest, carbon flux, dissolved organic matter, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), headwater streams, Wildfire

Although stormwater management ponds (SWMPs) are frequently used to mitigate flooding in urban areas, we still do not fully understand how these systems impact water quality in a watershed. Currently, most research focuses on the effectiveness of SWMPs to retain nutrients during high flows, even though there is potential for internal nutrient releases to occur in these systems during low flows. To investigate if SWMPs act as nutrient sources or sinks during low flow conditions, we analyzed how sewershed characteristics, pond properties, and hydrological and limnological factors influenced nutrient dynamics and stoichiometry in 10 SWMPs. Our study ponds were located in Peterborough, Whitby, and Richmond Hill, which are urbanized municipalities in southern Ontario, Canada. During October 2010 to 2011, we took monthly measurements of various carbon (C), nitrogen (N), and phosphorus (P) forms. We collected samples in the inlets, permanent pools, and outlets to determine any changes in concentrations, loads, and stoichiometric ratios into and out of the ponds. At the time of sampling, we also measured a variety of hydrological and limnological parameters. Our findings indicate that more urbanized sewersheds with higher drainage densities tend to have higher inflowing particulate and dissolved nutrient loads. In addition, we found that pond properties such as depth, length-to-width ratio, volume, and age differentially influence the retention of particulate and dissolved C, N, and P forms. Influential hydrological and limnological factors were antecedent moisture conditions, season, and thermal stratification. We found higher particulate P concentrations near the sediments when the catchments were drier and the ponds were ice-free and stratified. As well, we found higher outflowing stoichiometric ratios for DOC:TDN and DOC:TDP. This indicates an enrichment of C compared to N and P and suggests biogeochemical processes may be occurring in SWMPs. Overall, our results demonstrate that SWMPs are complex aquatic systems, and we need to consider biogeochemical processes in our design and maintenance activities, so that the effectiveness of SWMPs is not compromised during low flow conditions as a result of internal nutrient releases.

Author Keywords: Carbon, Nitrogen, Phosphorus, Urban biogeochemical cycling, Urban stormwater pond

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

Phosphorus is the growth-limiting nutrient in freshwater environments. Dissolved organic phosphorus (DOP) refers to phosphorus within dissolved organic matter (DOM). Much of DOP is bioavailable, but it is poorly understood due to its complexity. This thesis explores the export DOP to Lake Erie from its tributaries, by investigating its speciation and concentration seasonally through weekly sampling of two tributaries and spatially across a river to lake transect. The rivermouth was a site of rapid transition, with lower concentrations of DOP in the lake than in the river and a greater proportion of P as DOP in the lake. Phosphomonoesters and aromatic DOM were coupled in the medium-sized Grand River, but not in the Upper Great Lakes-influenced Detroit River. Phosphodiesters and highly processed DOM were coupled in the Detroit River, but only during periods of low terrestrial inputs. Finally, we found that DOP is a large contributor to tributary phosphorus exports.

Author Keywords: dissolved organic matter, dissolved organic phosphorus, enzymatic hydrolysis, Lake Erie, nutrient export, rivermouth

Rare earth elements (REEs) are in high demand globally for the green transition and high technologies. The growing demand leads to their release into aquatic ecosystems from various point and non-point sources, which creates urgency to investigate their fate and enrichment. This thesis further investigates the biogeochemical fate and REE uptake mechanisms throughout aquatic ecosystems. Rare earth element concentrations and fractionations were quantified to determine the natural uptake mechanism of three REE exposure pathways (dissolved, diet, and particulate) into aquatic organisms. Pelagic organisms accumulated heavy REEs, indicating they primarily uptake dissolved REEs. Benthic organisms were characterized by REE patterns specific for diet and particulate REEs. Furthermore, lanthanum (La) enrichment was investigated in a lake treated with La-based coagulants using La anomalies. Lanthanum enrichment in the water and organisms were directly related to La dispersion from sediments. This research provides information on preferential exposure pathways and REE enrichment in aquatic ecosystems.

Author Keywords: bioaccumulation potential, fractionations, lanthanum enrichment, metal organotropism, rare earth elements, uptake mechanisms

Recovery of forest soils from chronic acidification can be enhanced with the use of non-industrial wood ash (NIWA). Non-industrial wood ash is alkaline and contains high concentrations of macronutrients, but trace metal concentrations must be evaluated to limit risk of metal toxicity following application. Additionally, understanding how different forest ecosystem components respond to NIWA is essential to inform current policy regulating its use as a soil amendment. This study evaluated the response of sugar maple (Acer saccharum) sap yield and chemistry, the response of soils beneath maple, American beech (Fagus grandifolia) and mixed species canopies, and maple and beech fine roots, foliage, seedling abundance, and understory vegetation abundance and composition to an application of 6 Mg ha-1 NIWA. Eight 40 x 40 m plots were established in a hardwood stand in Bracebridge, Ontario and were sampled prior-to and up to two years following application of NIWA (n = 4). Non-industrial wood ash significantly increased organic horizon soil pH and macronutrient (Ca, Mg, and K) concentrations with increases in Mg and K extending to the mineral soils. Significantly higher concentrations of some trace metals (Al, Fe, Mn, Cd, Cu, Pb, Zn) were also observed, but these were restricted to the organic horizons. Sugar maple sap, pH, and sweetness were unaffected by NIWA application, and while increases were observed in nutrient and metal concentrations in sap, the differences were small and variable between years, and all concentrations were consistent with those commonly found in maple sap. Fine root biomass of maple and beech trees was not affected by NIWA application, but higher concentrations of K and Mg were observed in the roots of both species, consistent with higher concentrations observed in the mineral soil horizons beneath both species' canopies. Only significant increases were observed in K in sugar maple foliage. Both critical foliar concentrations and diagnosis and recommendation integrated system (DRIS) norms for sugar maple did not indicate mineral nutrient deficiencies at this site; although this site was acidic and nutrient-poor, this may account for the lack of differences observed, particularly between species. Changes observed in understory vegetation were driven by years rather than between treatments. These results suggest that moderate doses of NIWA can provide significant decreases in soil acidity and increase nutrient availability, with limited increases in metal concentrations that are primarily restricted to the organic horizons.

Author Keywords: American beech, metal toxicity, Non-industrial wood ash (NIWA), sap sweetness, sap yield, sugar maple