Abstract
During wildfire season in the western US, fire retardant chemicals are dropped from aircraft in an effort to control the spread of fire. Fire retardant dropped on sites that are not actively burning results in exceptionally high soil nitrogen (N) and phosphorus (P) "fertilization" effect on wildland soils impacting terrestrial and aquatic ecosystems. Herein, we used microdialysis to evaluate the short-term spatiotemporal dynamics of soil inorganic N and ortho-P fluxes in response to wood pyrogenic carbon (PyC) on soils receiving fire retardant (Phos-Chek) in a 28-d column experiment. Retardant additions to soil induced dramatic increases in soil inorganic N and ortho-P flux rates. The addition of wood PyC to soils with retardant significantly and immediately reduced ortho-P flux rates at multiple depths (1, 5, and 10 cm) and reduced NH4+ flux rates at 10 cm while retaining flux rates at 1 and 5 cm. These effects were observed throughout the course of the experiment and were more pronounced towards the end of the experiment. By d-28, PyC significantly reduced the NH4+, NO3-, and ortho-P accumulation on ionic resins at soil column bottoms by 50%, 52%, and 43%, respectively. The application of wood PyC may be effective at buffering excess nutrient fluxes from fire retardant and reduce short-term nutrient leaching in unburnt forest soils exposed to fire retardant.