Wildfire Effects on Stream Metabolism Across Gradients of Time and Fire Severity in an Idaho Wilderness Watershed

As climate change shifts fire regimes, it is increasingly important to understand stream ecosystem responses to fire. How stream metabolism responds remains largely unexplored. We investigated effects of fire severity, time since burn, and watershed characteristics on stream metabolism in a wilderness watershed of central Idaho. We estimated metabolism using observed diel dissolved oxygen, temperature, and irradiance to model diel oxygen dynamics over 3-8 day periods in 18 2^nd- to 5^th-order streams varying in fire history. From modeled oxygen dynamics, we inferred rates of respiration supported by different carbon pools. Results suggest that stream order, aspect, gradient, and post-fire riparian canopy recovery influence stream metabolic state (indexed by P:R) and the dominant carbon pool supporting stream respiration. Heavily shaded streams—both unburned, and severely burned with  post-fire riparian regrowth—were heterotrophic, whereas streams with less canopy recovery were autotrophic. A metabolism model allowing for respiration from an autochthonous carbon pool performed better than a single-source carbon model in 16 of 18 streams; in all but the two most heterotrophic streams, >50% of total respiration derived from an autochthonous carbon pool.