Koprivnjak, Jean-François

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

Environmental and seasonal processes are important watershed drivers controlling the amount, composition, and fate of dissolved organic matter (DOM) in aquatic ecosystems. We used ten months of water samples and eight months of bioassay incubations from two

contrasting catchments (agriculture and natural, forested) to assess the effects of seasonal variability on the composition, export, and biodegradability of DOM. As expected, the DOM composition and exports were more allochthonous-like and autochthonous-like in

the forest and agriculture streams, respectively. However, we found no relationship between DOM composition and biodegradability in our study, suggesting that broad environmental factors play a large part in determining bioavailability of DOM. We found that both differences between the catchments and seasonal variability in hydrology and water temperature cause shifts in DOM composition that can affect exports and potentially affect its susceptibility to microbial activity. More research is needed to fully understand the impact of land use and temporal variability on bioavailability and delivery to downstream ecosystems.

Author Keywords: Bioavailable dissolved organic carbon, Biodegradability, Dissolved organic matter, Export, Seasonality, Streams

This study assesses the bioavailable metal (Cu, Ni, Zn, Pb) species in the Athabasca-Mackenzie watersheds using diffusive gradient in thin films (DGT) devices. Metal toxicity is not only based on the concentration of metal in natural waters, but also on the nature of metal species. Four main forms in aquatic systems are: free ion, inorganic species, DOM bound (humic) species and metal colloidal species. The free ion and inorganic species and very small humic species are known as DGT-labile species and, are considered to be more bioavailable to micro-organisms due to the size and thus may be toxic to microorganisms. In this study, DGT devices were applied to (1) monitor the DGT-labile metal species in the lower Athabasca River and the Mackenzie River watershed and (2) assess the DGT-labile metal concentrations on temporal and spatial scales. In the lower Athabasca River, comparison between the DGT results and the Windermere Humic Acid Model (WHAM) calculation indicated good agreements for all metals when the precipitated iron(III) hydroxide was assumed as an active binding surface. No significant variations in labile species were found over 2003-2012 (RAMP database) despite the development of oil sands. In the Mackenzie River, no significant difference in DGT-labile metal concentrations and DOC concentrations was found in yearly basis 2012-2014. Only DOC was lower in August (6.98 and 3.85 ppm, respectively; p< 0.05) due to dilution from heavy rain events. Spatially, DGT-labile Cu and Ni in the downstream Mackenzie River were higher than upstream (1.79 and 0.58 ppb for Cu, 1.68 and 0.77 ppb for Ni, 4.06 and 6.91 ppm for DOC; p < 0.05). Overall the in situ measurements of metals constitute a benchmark for future studies in water quality and be helpful in environmental management in Alberta and the Northwest Territories in Canada.

Author Keywords: Athabasca River, DGT, Mackenzie River, Speciation, Trace Metal, WHAM