Fine sediment impacts on water treatability in fire impacted watersheds: Quantification of downstream propagation and water quality threats

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Forests are the primary source of drinking water for > 58% of the largest urban and rural communities as well as most Indigenous communities in Canada. Ironically, the high quality of these water resources make them vulnerable to severe large scale landscape disturbance such as those produced by wildfire. Climate associated changes in fire weather conditions over the past two decades have resulted in rapidly increasing occurrence, extent, and severity of major wildfire disturbances in critical forested source water regions of western North America. The threat of wildfire on sediment and associated nutrient dynamics in rives draining forested regions may pose a real risk to water supply and ecosystem services in many regions in Canada and across the globe. Despite the economic and environmental significance of wildfire and threats to the provision of safe drinking water, relatively few studies have examined the propagation of fine sediment in rivers draining burned watersheds and the delivery of these materials to reservoirs. Little is known about whether this deposited bottom sediment is a sink or source of phosphorus or if it has the potential to proliferate the growth of cyanobacteria which can challenge water treatment processes. Given that forested snow melt dominated slopes of the eastern slopes of the Rocky Mountains are critical water supply regions in Canada and the United States, knowledge gained from this research is relevant to water suppliers where source waters generally originate from forested landscapes. Results of the proposed research will improve knowledge of the transport processes and water quality impacts of post fire sediment and associated phosphorus in rivers at the large basin scale and evaluate the risk to water quality in downstream environments such as lakes and reservoirs. Knowledge gained from the proposed research will provide scientific insights to inform reservoir management strategies to evaluate the risk of fine sediment from wildfires to water treatability and related challenges to the provision of safe drinking water.