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. 2025 Jun 17;59(23):11853-11861.
doi: 10.1021/acs.est.5c04555. Epub 2025 Jun 7.

Lasting Impacts of Wildfire Retardant on Phosphorus Storage and Downstream Transport in a Rocky Mountain Stream

Madelyn M Lux  1 , Uldis Silins  1 , Michael J Wagner  2 , Eamon R Turner  1 , J Jeremy Fitzpatrick  1 , Erin A Cherlet  1 , Kirk Hawthorn  3 , Craig Harriott  3 , Micheal Stone  4 , Kathleen M Beamish  1 , Monica B Emelko  5
Affiliations

Lasting Impacts of Wildfire Retardant on Phosphorus Storage and Downstream Transport in a Rocky Mountain Stream

Madelyn M Lux et al. Environ Sci Technol. .

Abstract

Aerial application of fire retardants is a critical tool in wildland fire suppression but can impact aquatic ecosystems if accidentally misapplied into watercourses. However, exceedingly few studies have documented actual water quality impacts of such misapplications. Here, we explore the short- and longer-term effects of an operational misapplication of PHOS-CHEK LC95A into a Rocky Mountain stream on (a) water quality, (b) streambed storage and release potential of soluble reactive phosphorus (SRP), (c) its downstream transport, and (d) effects on periphyton productivity. Two weeks after the retardant drop, streambed SRP and its potential release into the stream were 2.6-3.0 times greater (p < 0.014) at the drop site than at a reference site above the drop, yet the greatest increases in aqueous stream SRP occurred 1 km downstream of the drop. One year later, while streambed SRP at the drop site declined by 34%, downstream transport of retardant residues and streambed-bound SRP strongly increased streambed and stream SRP 1.5-6.1 km below the retardant drop. The lasting effects of the retardant observed in this study reinforce the importance of continued refinement of air tanker operational guidelines and enhanced operational attention to protecting critical watersheds during fire suppression operations.

Keywords: PHOS-CHEK LC95A; equilibrium phosphorus concentration (EPC0); soluble reactive phosphorus (SRP); streambed.

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Figures

1
1
Photograph of North Racehorse Creek immediately below the drop site shortly after the accidental retardant drop, August 15, 2020 (photo credit Government of Alberta).
2
2
Map of study area, sampling sites, Meteorological Service of Canada (MSC) and Water Survey of Canada (WSC) climate, and hydrometric stations. Flow direction is from west (left) to east. The retardant was dropped into N. Racehorse Ck. at site 2. A small black dot south of site 2 indicates the fire CWF-114 location and size.
3
3
Streambed sediment soluble reactive phosphorus (SRP) sorption isotherms in (a) North Racehorse Creek, September 2020, (b) downstream in Racehorse Creek, September 2020, (c) North Racehorse Creek, September 2021 (1 year later), and (d) downstream in Racehorse Creek, September 2021 (1 year later).
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4
Streambed phosphorus release potential (PRP) and stream SRP above, at, and downstream of the retardant drop in September 2020 and September 2021 (1 year later). Bars indicate mean PRP (+1 std. error), and symbols indicate stream SRP.
See this image and copyright information in PMC

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