High-frequency community-based monitoring to characterize phosphorus loads in three major tributaries of Lesser Slave Lake, Alberta

This study describes a high-frequency community-based monitoring program conducted by the Driftpile Cree Nation between April and October 2022 to characterize phosphorus loads in the South Heart, Driftpile, and Swan Rivers, which are major tributaries of Lesser Slave Lake. The program aimed to refine estimates of tributary phosphorus mass loads to the lake by collecting frequent concentration measures, especially during high flow conditions, and relating them to continuous flow data. The high-frequency sampling resulted in 25 samples from each river over seven months. Measured total phosphorus (TP) concentrations in the Swan and Driftpile Rivers were higher than previously reported, especially during peak flow conditions. In the South Heart River, TP concentrations were consistently higher than previously reported, irrespective of flow. The combined semi-annual TP load for the three tributaries in 2022 was approximately 240 tonnes, much greater than previous annual estimates of between 78 and 83 tonnes. The Driftpile River, with a semi-annual TP load of 72.4 tonnes, showed the largest difference from earlier annual estimates of <10 tonnes. These higher tributary TP load estimates suggest that efforts to reduce tributary TP loads in order to reduce eutrophication effects in Lesser Slave Lake could be worthwhile. Additional insights into the challenges and advantages experienced in a community-based monitoring program of this type are included.