Abstract
Wildfires have become larger and more severe in recent decades. Fire retardant is one of the most common wildfire response tools to protect against loss of life and property. Previous studies have documented various effects of fire retardant, which commonly contains chemicals used in fertilizers, on plant and invertebrate community composition. This mesocosm study investigated the effects of fire retardant on water quality and plant and invertebrate communities in California vernal pools. This study found that fire retardant caused water quality conditions to shift from oligotrophic to eutrophic with strong correlations between fire retardant and phosphates, nitrates, conductivity, and chlorophyll-a. Algal cover increased with added fire-retardant concentration. Shifts in invertebrate and plant communities occurred even at relatively low fire-retardant concentrations. Abundance of passive dispersers (crustaceans) peaked at medium concentrations of fire retardant, but time also influenced the relationship between fire retardant and passive invertebrate abundance. Active disperser (insects) abundance increased with increasing fire-retardant concentration and invertebrate richness peaked at medium concentrations. This study informs land managers, government agencies, and the public of the side-effects of fire-retardant use on populations, communities, and water quality of freshwater ecosystems.