title: Sediment-phosphorus dynamics can shift aquatic ecology and cause downstream legacy effects after wildfire in large river systems.
abstract: Global increases in the occurrence of large, severe wildfires in forested watersheds threaten drinking water supplies and aquatic ecology. Wildfire effects on water quality, particularly nutrient levels and forms, can be significant. The longevity and downstream propagation of these effects as well as the geochemical mechanisms regulating them remain largely undocumented at larger river basin scales. Here, phosphorus (P) speciation and sorption behavior of suspended sediment were examined in two river basins impacted by a severe wildfire in southern Alberta, Canada. Fine-grained suspended sediments (<125 μm) were sampled continuously during ice-free conditions over a two-year period (2009-2010), 6 and 7 years after the wildfire. Suspended sediment samples were collected from upstream reference (unburned) river reaches, multiple tributaries within the burned areas, and from reaches downstream of the burned areas, in the Crowsnest and Castle River basins. Total particulate phosphorus (TPP) and particulate phosphorus forms (nonapatite inorganic P, apatite P, organic P), and the equilibrium phosphorus concentration (EPC0 ) of suspended sediment were assessed. Concentrations of TPP and the EPC0 were significantly higher downstream of wildfire-impacted areas compared to reference (unburned) upstream river reaches. Sediments from the burned tributary inputs contained higher levels of bioavailable particulate P (NAIP) - these effects were also observed downstream at larger river basin scales. The release of bioavailable P from postfire, P-enriched fine sediment is a key mechanism causing these effects in gravel-bed rivers at larger basin scales. Wildfire-associated increases in NAIP and the EPC0 persisted 6 and 7 years after wildfire. Accordingly, this work demonstrated that fine sediment in gravel-bed rivers is a significant, long-term source of in-stream bioavailable P that contributes to a legacy of wildfire impacts on downstream water quality, aquatic ecology, and drinking water treatability.
authors: Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
authors: Monica B
authors: MB
authors: Emelko
authors: Department of Geography and Environmental Management, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
authors: Micheal
authors: M
authors: Stone
authors: Department of Renewable Resources, University of Alberta, Edmonton, AB, T6G 2H1, Canada.
authors: Uldis
authors: U
authors: Silins
authors: Department of Geography and Environmental Management, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
authors: Don
authors: D
authors: Allin
authors: Sustainable Soils and Grassland Systems Department, Rothamsted Research, North Wyke, Okehampton, EX20 2SB, UK.
authors: Adrian L
authors: AL
authors: Collins
authors: Department of Renewable Resources, University of Alberta, Edmonton, AB, T6G 2H1, Canada.
authors: Chris H S
authors: CH
authors: Williams
authors: Department of Renewable Resources, University of Alberta, Edmonton, AB, T6G 2H1, Canada.
authors: Amanda M
authors: AM
authors: Martens
authors: Department of Forest Engineering, Resources and Management, Oregon State University, Corvallis, OR, 97331, USA.
authors: Kevin D
authors: KD
authors: Bladon
mesh_terms: D000327:Adsorption; D000416:Alberta; D005390:Fires; D019015:Geologic Sediments / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D012621:Seasons; D014874:Water Pollutants, Chemical / Q000032:analysis*; D060753:Water Quality
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus
keywords: climate change; cumulative watershed; effects; eutrophication; land disturbance; phosphorus; sediment; treatability; wildfire