Effects of Wildfire and Fire Retardants on Nutrient Transport in California Watersheds

Science Center Objects

Large wildfires have increased in size and frequency in the western United States over the past several decades. This has led to increased soil erosion and the transport of sediment containing nutrients into streams and reservoirs. Excess nutrients typically lead to the increased production of algae which can then lead to low levels of dissolved oxygen. This degrades the habitat for fish and wildlife, as well as having negative impacts on the drinking water supply and human recreation.

Photo of a plane dropping flame retardant on a wildfire

Plane dropping fire retardant on a wildfire

In addition, each year millions of liters of fire-retardant chemicals are applied to wildfires across the nation. The use of these retardants could also have significant effects on downstream nutrients. The aim of this study will be to determine which nutrients are likely to increase in concentration in areas affected by wildfire in the western U.S., and whether the use of fire retardants may exacerbate the situation. Specifically, wildfires and related use of fire retardant could have significant effects on downstream nutrients and related water-quality conditions in reservoirs owned and operated by the Bureau of Reclamation (BOR). A modeling approach could help the BOR implement best management practices to protect water quality and benefit the environment.

Science Plan

Working with the BOR, with lab support from California State University, Chico, the USGS will provide technical assistance to the BOR as it develops a watershed-based model of nutrient transport in relation to the use of fire retardants in areas affected by wildfire. This effort will be divided into several tasks including: measuring the effects of fire retardants on the amount of nitrogen (N) and phosphorus (P) in water run-off, the analysis of affected water and soil samples, and the creation and testing of the model itself.

The two main sampling sites are:

  • The site of the 2018 River Fire area, Lake County, CA
  • The site of the 2019 Kincade Fire area, Sonoma County, CA

Timeline and Budget

The project will commence in June of 2020 and is expected to be complete by end of FY 2021. The current approved budget is $20,000 for FY 2020 and $25,000 for FY 2021.