Biogeochemical assessments of rapidly changing glacial rivers on the  eastern slopes of the Canadian Rocky Mountains
Creators: Serbu, Jessica A.
Publisher: name: University of Alberta Library
Year: 2024

<p>Climate change is driving the loss of alpine glaciers globally, yet investigations about the water quality of rivers stemming from them are few. In Chapter 2, we provide an overview of a biogeochemical dataset containing 200+ parameters that we collected between 2019-2021 from 14 sampling sites along the headwaters of three such rivers (Sunwapta-Athabasca, North Saskatchewan, and Bow). Notably, their watersheds spanned glacierized to montane altitudinal life zones over 100 km reaches on the eastern slopes of the Canadian Rocky Mountains in Banff and Jasper National Parks, Alberta. We used regional hydrometric datasets to accurately model discharge at our sampling sites. We created a Local Meteoric Water Line (LMWL) using riverine water isotope signatures and compared it to collected regional rain, snow, and glacial ice signatures. Principal component analyses of physicochemical measures revealed distance from glacier explained more data variability than other spatiotemporal factors (i.e., season, year, or river). Discharge, chemical concentrations, and watershed areas were then used to model site-specific open water season yields for 25 parameters. Chemical yields followed what would generally be expected along river continuums from glacierized to montane altitudinal life zones, with landscape characteristics driving chemical sources and sinks. Particulate chemical yields were generally highest near source glaciers with proglacial lakes acting as settling ponds, whereas most dissolved chemical yields varied by parameter and site. As these headwaters continue to evolve with glacier mass loss, the dataset and analyses presented here can be used as a contemporary baseline to mark future change against. </p>

<p>Geochemical weathering is especially pronounced in glacierized watersheds due to large quantities of fresh glacial flour. In Chapter 3, we assessed types and magnitude of geochemical weathering in the same three Canadian Rocky Mountain eastern slope rivers described in Chapter 2. We used multiple lines of evidence to quantify geochemical weathering along our ecologically complex river transects and across seasons and years. CO2 was highly undersaturated, and CO2 fluxes most negative, at sampling sites nearest source glaciers, while calcite saturation indices were mostly below zero. The chemostatic behavior of Ca2+, Mg2+ and dissolved inorganic carbon (DIC) indicated carbonate weathering at all sites, though relative Si inputs increased downriver. Molar concentration ratios showed H2CO3 was the key proton donor to weathering reactions. The range of 87Sr/86Sr ratios indicated a lack of lithological contrasts, while δ34S-SO4 was similar to global evaporites, and δ13C-DIC was the most isotopically heavy at sites nearest source glaciers. Organic matter and silicate weathering contributions to the DIC mass balance increased moving downriver. Yet, carbonate weathering and atmospheric CO2 remained the dominant sources of DIC throughout our rivers, with &gt;50% contribution even 100 km downriver of source glaciers. On a global scale, we suspect these patterns in types and magnitude of geochemical weathering are common across glacierized watersheds. As glaciers retreat due to climatic warming and we see an encroachment of downriver altitudinal life zones, sources of DIC may shift. </p>

<p>Finally, in Chapter 4, which was initiated during the 2020 COVID-19 shutdown, we quantified how efficiently the contaminants total mercury (THg) and methylmercury (MeHg) were removed from North Saskatchewan River water along the different stages of drinking water production at the E.L. Smith Drinking Water Treatment Plant in the municipality of Edmonton, Alberta. Water treatment processes involved chemical additions for flocculation, followed by clarification, filtration, and UV treatment prior to water being stored in reservoirs for later distribution. 75% THg and 66% MeHg were removed from river water following chemical additions and clarification. A further 9.8% THg and 31.8% MeHg was removed during the filtration stage, while 1.5% THg and 0.8% MeHg more was removed during UV treatment. The final product water was an order of magnitude less than Canada’s maximum allowable concentration for drinking water. We also examined how yields of Hg changed along the North Saskatchewan River as it flowed from its glacial headwaters described in Chapter 2 to where water was removed for drinking water production 534 km downriver. In 2020, mean open water season (1 May to 31 October) THg yields varied greatly from 0.127 to 1.29 g km-2 at headwater and mid-river sites but increased to 1.89 g km-2 at Edmonton, suggesting value in the protection of source watersheds.</p>