Long-term impact of wildfire on particulate phosphorus forms and phosphorus sorption behavior of suspended river sediment in the Crowsnest River basin, Alberta, Canada

The effects of wildfire on catchment hydrology, sediment production and nutrient yield have been well documented. However, lesse is known about the downstream propagation of fire-modified materials, their nutrient composition and potential effects to downstream environments. This study examines the long-term impact (6-7 years) of the 2003 Lost Creek wildfire on particulate phosphorus forms (NAIP, AP, OP) and phosphorus sorption behavior of suspended river sediment at a large regional scale (554 km2) in the Crowsnest River basin, Alberta, Canada. Total P concentrations were similar among burned and unburned river sediments but the mean bioavailable NAIP fraction remained approximately 70% greater and the organic P was > 2-fold higher in sediments from five burned tributary watersheds compared to the reference catchment. In a series of batch experiments, fire impacted sediments desorbed significantly more P than reference sediments. Because of the key role of phosphorus in regulating aquatic productivity in oligotrophic mountain streams, the results highlight the risk of a large scale and long-term legacy of wildfire in some mountain river systems and their potential impact on the nutrient dynamics of reservoirs used for drinking water supply.