Nutrient emissions from prescribed fire in Lake Tahoe Basin: Implications from field and laboratory observations

Abstract

Prescribed fire is a common management practice for reducing excessive forest fuel loading to minimize the risk of wildfire. However prescribed fire may impact air and water quality by releasing nutrients from soils and vegetation upon combustion. This study assesses the carbon (C) and nitrogen (N) release as affected by fuel moisture during a prescribed fire near Incline Village (NV) following mechanical thinning. The field component of this study involved a pre- and post-fire fuel inventory to estimate C and (in)organic N losses and chemical speciation under fall fuel moisture conditions. The lab component of the study further investigated effects of moisture on nutrient release and speciation by artificially wetting fuels followed by combustion in a custom designed combustion chamber allowing for direct measurement of amounts and composition of nutrients released into the air. Results from the field show changes to moisture content as a result of the burn, and relate moisture conditions to fuel, C and N reductions. Changes to extractable N are also included. The combustion experiment showed that increasing fuel moisture causes increases in total particulates, including C and N species, and gaseous NH₃ emissions for several fuel types, with soils showing the only trend for gaseous NO_x emissions. Nutrient emission factors were highest for litter and leaves especially at the higher moisture levels. Our findings help land managers to better understand how fuel moisture affects fuel consumption and nutrient release from prescription fire. This will allow managers to create management practices that maximize fuel reductions while minimizing environmental impacts within the Lake Tahoe Basin.