LB 18-186 - Effects of Fire Retardant on California Vernal Pool Community Composition

Background/Question/Methods:

Wildfires continue to threaten California and have recently become more frequent and intense. As a response, federal agencies such as the U.S. Forest Service (USFS) treat the perimeter of wildfires with fire retardant in attempt to control the fire. Previous studies have focused on the effects of fire retardant on individual species, but few have examined the effects on plant and invertebrate communities within an ecosystem. We investigated the effects of increasing concentrations of fire retardant on invertebrate and plant abundance and biodiversity in California vernal pool mesocosms. Three fire-retardant concentrations (Control, Diluted, Undiluted) were applied in four replicates of each treatment at the California State University, Sacramento Arboretum. Mesocosms were lined with vernal pool soil that contained common vernal pool plant seeds and invertebrate eggs. California vernal pools are imperiled ecosystems that support dozens of threatened and endangered species. Mesocosms were filled from March to May 2022, and sampling of organisms and water quality occurred every two weeks. Water quality measurements included pH, turbidity, conductivity, chlorophyll a, and phosphates.

Results/Conclusions:

Fire retardant was found to have effects on vernal pool water quality, biodiversity, and community composition. Conductivity and phosphates increased, and pH decreased with fire retardant addition. Total species richness and abundance increased over time and decreased with increasing fire-retardant concentration. Additionally, fire retardant addition caused an increase in mosquito abundance. Water quality shifted from oligotrophic to eutrophic conditions with increasing fire-retardant application. If vernal pools are subject to fire retardant misapplications during emergency fire retardant application, long term monitoring efforts will be needed to ensure that wildfire management does not come at the risk of biodiversity loss in associated freshwater ecosystems.