Seasonal and Temporal Variations of Chloride Level in Riverine Environment
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AbstractChloride is one of essential elements for the health of all organisms, humans included; however at the elevated level, chloride has detrimental impacts on ecosystem. Chloride originates from both natural sources and anthropogenic sources (e.g., municipal treated wastewater and emission from industries), which suggests that chloride level in natural water bodies (e.g., rivers) is affected by both natural factors (e.g., hydro-meteorological variables) and anthropogenic activities. Among various anthropogenic activities, the application of road salts, which is a common practice to improve the driving condition of roads in winters across Canada, has been shown to attribute to the elevation of chloride level. The impact of the use of road salts on riverine chloride level can be seasonal (during snow-melt season) and over a prolonged period. Furthermore, river flow primarily drives the seasonal variation of riverine chloride. Therefore this thesis aimed to investigate the intra-annual/seasonal variation and the inter-annual/temporal change of chloride in rivers/streams and to assess the impact of the application of roads salts on chloride across Canada through statistically analyzing available data including chloride concentration, the use of road salts, and flow datasets. The seasonal variation of chloride was detected and chloride was negatively correlated with river flow in general. However, the seasonal variation pattern of chloride and its dependency on flow appeared to be different between large and small rivers in a certain degree. The temporal change (especially increasing trend) in chloride was found at many stations. It was identified that either flow, anthropogenic activities, or their combination is ascribed to cause the temporal change of chloride. The increasing riverine chloride concentration at many stations was qualitatively linked to the increase of the application of road salts, while more elaborated research is recommended for quantitative investigation. In addition, the Code of Practice for the Environmental Management of Road Salts, which was published in 2004 by Environment and Climate Change Canada (former name, Environment Canada) to better manage the use of road salts in order to mitigate its impact on chloride, appeared to help in reducing the increasing trend of chloride level.
Schulich School of Engineering