Gueguen, Celine

The Hudson Bay region is a sensitive environment, where anthropogenic (e.g., dams, diversions, and/or reservoirs) impacts have increased in recent decades, potentially influencing the functioning of the ecosystem. Dissolved organic matter (DOM) entering Hudson Bay comes from both terrestrial (allochthonous) and aquatic (autochthonous) sources. The chemical composition of DOM is important, as it controls carbon biogeochemistry, nutrient cycling, and heat exchange. In rivers, estuaries, and oceans, photochemical processes and microbial degradation play a significant role in the chemical composition of DOM. Yet, our knowledge is scarce into how photochemical and microbial processes effect DOM composition specifically in Arctic aquatic systems making it difficult to predict how the carbon cycle will respond to a changing environment. This Ph.D. thesis addresses: (1) the composition of photochemically altered autochthonous and allochthonous DOM; (2) the photochemical transformations of DOM in surface waters of Hudson Bay; and (3) the microbial transformations of DOM in Hudson Bay surface waters. Using multiple analytical techniques, this work demonstrated that photochemical and microbial effects were different for light absorbing DOM compounds and ionisable DOM analyzed by Fourier transform-ion cyclotron-resonance-mass spectrometry (FT-ICR-MS). Based on FT-ICR-MS analysis, microbial processes had a greater impact on the molecular composition of allochthonous DOM originating from riverine sources and estuary whereas photochemical processes were the dominant mechanism for degradation of autochthonous DOM in Hudson Bay. Photochemical processes significantly decreased colored dissolved organic matter (CDOM) and fluorescence dissolved organic matter (FDOM) loss whereas microbial degradation was minimal in Hudson Bay river, estuary, and coastal waters. The results of this thesis highlight the importance of photochemical and microbial alteration of DOM in Arctic regions, two processes that are expected to be enhanced under climate change conditions.

Author Keywords: Carbon cycle, Field flow fractionation, Microbial transformation, Optical properties, Photochemical degradation

This thesis investigated coloured and fluorescent dissolved organic matter in the Canada Basin, Arctic Ocean from 2007 to 2017. The first interannual time-series of its kind in the Canada Basin incorporated the use of EEM-PARAFAC to validate a seven-component model. Statistical temporal tests revealed (1) an increasing protein-like intensity in the upper polar mixed layer (UPML); (2) increasing intensities of humic-like components in the halocline due to increasing freshwater content; and (3) no change in DOM composition in deeper Atlantic waters (AW) congruent with the long residence time of the water mass (> 30 years). The significant decline in sea ice concentration was related to a decrease in humic-like FDOM due to enhanced photodegradation and an increase in protein-like FDOM, likely the results of increased biological activities in surface layers. This research provides evidence that the changes in physical and biological environment in the Arctic regions have already profound impacts on the composition and distribution of FDOM.

Author Keywords: absorbance, Arctic Ocean, dissolved organic matter, fluorescence, parallel factor analysis, time-series

Euglena gracilis is an enigmatic and adaptable organism that has great bioremediationpotential and is best known for its metabolic flexibility. The research done in this dissertation addresses (1) how growth conditions impact cellular composition, and (2) how chemometric approaches (such as statistical design of experiments and artificial neural networks) are viable alternatives to the conventional biosorption models for process optimization. Using high-resolution mass spectrometry for biosorbent characterization is a powerful way to assess the chemical characteristics of lyophilized and fractionated cells with high precision, especially to screen for compound classes that may have potentiality for rare earth element removal. Growth conditions impacted cellular composition and separated size fractions of cells yielded different molecular/chemical properties as described by compositional abundances, thus different biosorptive potential. Untargeted analysis demonstrated that exponential dark-grown cells with glucose supplementation were abundant in polyphenolic- and carbohydrate-like compounds, molecular species highly involved in rare earth element binding. Light grown cells had more heterogeneity and the highest molecular weighted fractions from light grown cells (fraction D) had the most abundances of polyphenolic- and protein-like structures. Chemometric modeling used identified the best and worst conditions for iii dysprosium sorption and showed that pH had the most significant influence on bioremoval. Bioremoval ranged from 37% at pH 8 to 91% at pH 3 at Dy concentration ranging from 1 to 100 μg L-1. The work presented in the PhD dissertation will aid in understanding the chemical characteristics of biosorbents by using a Van krevelen analysis of elemental ratios whether algal cells are grown in different environmental growth conditions, or when algal cell are size fractionated. This is especially applied for the screening for metal binding potentiality to Dysprosium. Chemometric methods provide an alternative method for the investigating factors for bioremoval, and applications for process optimization and for real-world applications. This dissertation will aid in understanding chemical characteristics when a biosorbent is grown in a given condition and which factors are important for rare earth element (REE) bioremoval. The significance of this work aims to look for alternate ways to screen biosorbents and using a more efficient experimental design for REE bioremoval.

Author Keywords: bioremoval, biosorption, chemometrics, dysprosium, euglena, mass spectrometry

The efficacy of the diffusive gradients in thin films (DGT) passive samplers to provide accurate measurements of free metal ions and those complexed with dissolved organic matter (DOM) was investigated. DOM controls the diffusive properties of DOM-complexed metal species in natural systems. Knowing the diffusion coeiffiecent (D) for DOM of different molecular weights (MW) and the major environmental variables influencing D is critical in developing the use of DGT passive samplers and understanding labile species. D and MW were determined for natural and standard DOM. No noticeable changes in DOM MW were observed during the diffusion process, suggesting that DOM remains intact following diffusion across the diffusive gel. Data analysis revealed that MW had the greatest influence on D, with a negative relationship between D and MW, except in tidal areas where ionic strength influence on D was significant. This study provides further characterization of the variables influencing D using the DGT technique.

Author Keywords: Diffusion coefficient, Diffusive gradients in thin films, Dissolved organic matter, Flow field-flow fractionation, Principal Component Analysis, UV-Vis Spectroscopy

Selenide is cited as a geochemically important selenium (Se) species, but it is unknown whether selenide is a stable aqueous ion in natural waters. The feasibility of using anoxic anion exchange chromatography (AEC) coupled to dynamic reaction cell-inductively coupled plasma-mass spectrometry to separate aqueous selenide was investigated with the goal of quantifying this anion to determine its importance in reducing waters.

It was possible to qualitatively identify selenide using AEC, but much of the aqueous selenide oxidises to Se0 faster than the separation procedure could be completed. AEC analyses of solutions containing polyselenides produced peaks for unidentified Se compounds, which have been assigned tentative structures Se2O22-, Se2O32-, and Se2O62- based on close matches in retention time to stable S compounds.

The results of this work show that aqueous selenide can be qualitatively observed in synthetic solutions using AEC, but it is unknown whether these conditions are relevant to natural waters.

Author Keywords: anoxic speciation, polyselenides, selenide, selenium geochemistry, selenium speciation, selenoselenate

This study presents a detailed assessment of the chemical speciation of aluminum and zinc in three streams of a small, acid-sensitive forested catchment on the southern edge of the Precambrian Shield.

Speciation analysis was achieved using an in-situ analytical technique known as Diffusive Gradient in Thin film (DGT) which measures labile metals, and a predictive computer algorithm (WHAM VI) which calculates metal species concentrations. Three types of DGT with different metal scavenging capabilities were used and a total of 11 deployments performed across four seasons. WHAM VI predictions showed that the organic fraction of aluminum was the main contributor to the dissolved concentrations in the main inflow stream (PC1) (~ 80 %) and the lake's outflow (PCO) (~ 75%); in the upland stream (PC1-08) the inorganic fraction contributed ~ 75%. For zinc the free ion was the single most important contributor to the dissolved concentration (< 90%) in all three streams. A comparative study of the DGT and WHAM methods showed an agreement between their inorganic concentrations during the spring season. Both methods indicate the greatest environmental impact for Al takes place during snow melt period in PCO and PC1-08 and in the summer for PC1. The greatest environmental impact for Zn predicted with WHAM VI, occurs during the spring in all three streams.

Author Keywords: Aluminum, DGT, Metal speciation, WHAM, Zinc

Perfluorinated carboxylic acids (PFCAs) are anthropogenic environmentally ubiquitous surfactants that tend to concentrate on water surfaces. This investigation looked at the effect of simulated rain on the atmospheric concentration of a suite of PFCAs (C2 - C12) above the bulk water system. Increased air concentrations of all PFCAs were detected during simulated rain events. Long chain PFCAs (>C8) were found to be much more concentrated in the air above the bulk water system than their short chain counter parts (

Author Keywords: aqueous aerosols, perfluorinated carboxylic acids, surfactants environmental fate, water to air chemical transfer

The damage to Sudbury's landscape from over a century of smelter and logging activity has been severe and impacts well documented. However, despite their abundance in the region, wetlands have received little attention. Recent studies have identified that nutrient limitation is as much a problem as metal toxicity and highlighted not only the importance of wetlands but also the need for more detailed studies examining the role of wetlands in the recovery of lakes. The objective of this work is to characterize the spatial and temporal variability in the geochemistry of 18 wetlands (poor fens) surrounding Sudbury, Ontario. Peat and water chemistry in the wetlands exhibited large spatial and temporal variability. Copper and Ni concentrations in surface peat decreased with distance from the largest smelter in the area, but water chemistry was also strongly influenced by natural factors such as climate, groundwater and peat carbon content. Redox processes contribute greatly to temporal variation in pore-water chemistry: the August and October campaigns were characterized by higher SO4, lower pH and higher concentrations of metals such as Ni, Cu and Mn compared with the May campaign. Other factors contributing to the temporal variability in pore water chemistry include DOC production, senescence and water source. Despite the large variability, soil-solution partitioning can be explained by pH alone for some metals. Modeling is significantly improved with the addition of other variables representing dissolved organic matter quality and quantity, sulphate concentration and hydrology.

Author Keywords: metal contamination, metal mobility, organic matter quality, peatland geochemistry

Extensive research has gone into measuring changes to the carbon storage capacity of Arctic terrestrial environments as well as large water bodies in order to determine a carbon budget for many regions across the Arctic. Inland Arctic waters such as small lakes and ponds are often excluded from these carbon budgets, however a handful of studies have demonstrated that they can often be significant sources of carbon to the atmosphere. This study investigated the CO2 cycling of tundra ponds in the Daring Lake area, Northwest Territories, Canada (64°52'N, 111°35'W), to determine the role ponds have in the local carbon cycle.

Floating chambers, nondispersive infrared (NDIR) sensors and headspace samples were used to estimate carbon fluxes from four selected local ponds. Multiple environmental, chemical and meteorological parameters were also monitored for the duration of the study, which took place during the snow free season of 2013.

Average CO2 emissions for the two-month growing season ranged from approximately -0.0035 g CO2-C m-2 d-1 to 0.12 g CO2-C m-2 d-1. The losses of CO2 from the water bodies in the Daring Lake area were approximately 2-7% of the CO2 uptake over vegetated terrestrial tundra during the same two-month period.

Results from this study indicated that the production of CO2 in tundra ponds was positively influenced by both increases in air temperature, and the delivery of carbon from their catchments. The relationship found between temperature and carbon emissions suggests that warming Arctic temperatures have the potential to increase carbon emissions from ponds in the future.

The findings in this study did not include ebullition gas emissions nor plant mediated transport, therefore these findings are likely underestimates of the total carbon emissions from water bodies in the Daring Lake area. This study emphasizes the need for more research on inland waters in order to improve our understanding of the total impact these waters may have on the Arctic's atmospheric CO2 concentrations now and in the future.

Author Keywords: Arctic, Arctic Ponds, Carbon dioxide, Carbon Fluxes, Climate Change, NDIR sensor

This thesis was designed to quantify absorbance and fluorescence characteristics of dissolved organic matter (DOM) in North Atlantic, Pacific and Arctic Oceans. DOM was described in water masses of distinct sources and formation pathways as well as in regions where environmental forcings such as deep water upwelling, enhanced biological activity and receipt of freshwater discharge were prevalent. Influence of sea ice on DOM in Beaufort Sea mixed layer (0 to 30 m) seawater was investigated based on sea ice extent as well as freshwater fractions of meteoric (f_mw) and sea ice melt water (f_sim) calculated from oxygen isotope ratio (δ18O). The effect of DOM exposure to simulated solar radiation was also assessed to determine the resilience of fluorescent fractions of DOM to photodegradation. This research aims to further our ability to trace DOM in marine environments and better understand its transformation pathways and predict its fate as part of the oceanic carbon cycle in a changing climate.

Author Keywords: Absorbance, Arctic Ocean, Dissolved organic matter, Fluorescence, Parallel Factor Analysis, Sea Ice