As the severity of megafires increases across the western U.S., ecosystem services such as nutrient uptake and removal may be affected. Megafires restructure ecosystems by removing vegetation, altering hydrology, and releasing sediment. We quantified the effects of megafire on aquatic nutrient cycles using the nutrient injections to quantify spiraling parameters. These methods characterize nutrient uptake kinetics, providing an ecosystem-level assessment of biological community and material attenuation capacity. We performed injections during the winter, spring, and summer at burned and unburned locations in central Utah. Unlike previous work, which has primarily focused on natural or semi-natural streams, we also included urbanized and agricultural stream locations, allowing us to assess the interactive effects of wildfire and land use.
Results/Conclusions
The megafires that occurred in 2018 burned 610 km2 in the Wasatch Mountains in central Utah. They affected multiple ecosystem types, including sagebrush steppe, pinion-juniper forest, oak-maple forest, and aspen-conifer forest. The nutrient injections revealed that nutrient spiraling lengths and uptake velocities changed seasonally and by ecosystem type. Surprisingly, land use had a larger effect on nutrient dynamics than the megafire, demonstrating the importance of considering multiple stressors when predicting ecological response to disturbance. Along those lines, multiple debris flows extended the period of disturbance and succession throughout the year following the wildfire. We conclude that while land use, including wastewater effluent, is the primary determinant of nutrient state in streams of this region, wildfire should be considered as an additional risk factor for nutrient release. Changes in light and nutrient availability following wildfire may be the biggest contributors to ecosystem state changes in the near future.