Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Geography & Environmental Studies

Program Name/Specialization

Environmental Science

Faculty/School

Faculty of Arts

First Advisor

Jason Venkiteswaran

Advisor Role

Associate Professor

Abstract

Many Canadians rely on surface water sources for drinking water, most of which is disinfected with chlorine. Dissolved organic carbon (DOC) can react with chlorine to form potentially carcinogenic disinfection by-products (DBPs). The concentration and composition of DOC influences the type and amount of DBP formed.

Lake water varies widely in DOC concentration and composition as a result of the surrounding landscape that influences the terrestrial load of DOC to lakes and the extent of in-lake processing of DOC. Twenty-seven lakes of similar lake size but with varying catchment sizes over several orders of magnitude created a unique opportunity to examine the influence of water renewal rate on DOC composition and subsequent DBP formation during chlorination in the drinking water treatment process.

DOC concentration of low order lakes was predictable from hydrologic water residence time (WRT) values, but as larger catchments with higher order lakes were considered, the isotopic WRT values explained more variance in DOC. However, WRT of an individual lake does not account for the upstream processing of DOC that occurs throughout the entire catchment containing several hydrologically connected lakes. The proportion of open water within the whole catchment (%OW) is able to explain more variance in DOC than lake WRT. Additionally, novel cryptic wetland (%CrWetland) data that identifies low-lying areas with the potential to generate DOC within the catchment further improved the prediction of DOC concentration and composition.

Lakes in catchments with lower %OW and higher %CrWetland are more likely to contain higher DOC concentrations and more allochthonous-like composition while those in catchments with higher %OW and lower %CrWetland have a greater proportion of autochthonous-like DOC. The high aromaticity and molecular weight of allochthonous-like DOC is related to high concentrations of DBPs from chlorination. However, some lakes with more autochthonous-like DOC still produced DBP concentrations well over the guidelines for drinking water limits. Therefore, further research is needed to identify precursors to DBP formation in order to efficiently disinfect surface lake water sources while eliminating the risk of high DBP levels.

This thesis provides a mechanistic understanding of DOC concentration and composition across a wide gradient of lake water residence times in relation to DBP formation during drinking water treatment processes. As climate change continues to alter surface lake water DOC concentration and composition, predicting DBP formation when surface lake water sources are disinfected with chlorine is increasingly important.

Convocation Year

2021

Convocation Season

Fall

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