Wildfire elevated legacy phosphorus in Alberta’s Crowsnest River, study finds


Resource extraction, wildfire, and municipal wastewater discharge are increasing particulate phosphorus levels along a 50-km stretch of the low-nutrient Crowsnest River, joint research from the University of Waterloo and the forWater Network has found.

The two-year field study in southwestern Alberta highlights the longitudinal water quality impacts of increasing landscape disturbances on fine riverbed sediments, as legacy phosphorus can promote algal blooms, water treatment challenges, and degrade ecosystem health for decades.

“While watersheds regularly experience many cumulative effects from natural and manmade disturbances, we see that climate change intensifies the extremes of those impacts,” said University of Waterloo Theme Leader and study co-author Mike Stone in a statement.

The researchers stated that the use of targeted watershed monitoring programs can be used to evaluate both water and sediment quality in rivers upstream of reservoirs to help utilities assess risks to water quality and treatment.

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Geochemical tracing approaches can also be used to distinguish the contributions of various nutrient sources, the study noted.

The analysis indicated that, although land disturbances such as farming and mining have impacted the entire watershed, “combined natural and anthropogenic disturbance is notably greater in the lower reaches of the river compared to the upper sub-watersheds.” The combined disturbances from the 2003 Lost Creek wildfire, as well as impacts from industrial, municipal, and agriculture sectors comprised a larger disturbance footprint within the lower half of the watershed.

The Crowsnest River sediment geochemical data suggest that the effects of the 2003 Lost Creek wildfire are still evident in the gravel-bed matrix some 13 years after the fire. The fire nearly destroyed the community of Crowsnest Pass, burning some 21,165 hectares over 26 days in late July.

“Bed sediments play an especially critical role in regulating nutrient dynamics in sediment-rich rivers such as the Crowsnest, where wildfire-induced biostabilization increases the shear stress that must be overcome to mobilize fine sediment, but also results in substantial increases in erosion depth, thereby releasing more suspended sediment and associated [phosphorus] to the water column at higher flow conditions,” the study states.

Other contributing authors of the study include Caitlin Watt, Monica Emelko, Uldis Silins, and Adrian Collins.


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