Umeå University's logo

Wildfires are a common disturbance in tropical grasslands and savannahs, but few studies have evaluated wildfire effects on the streams draining these ecosystems. Understanding these effects on aquatic ecosystems becomes critical as climate change increases fire frequency and intensity. This paper investigated the short-term (10 mo) impacts of a wildfire on a Brazilian headwater stream in a relatively pristine, shrubby grassland watershed. We determined pre- and post-fire indicators of stream functioning, including NH4-N and soluble reactive P (SRP) uptake lengths (Sw), rates (U) and velocities (vf), gross primary production (GPP), ecosystem respiration (ER), and aquatic emissions of CO2 and CH4. Post-fire GPP was 8x higher than pre-fire levels, whereas ER was similar between these periods. Pre-fire uptake metrics had higher uptake for NH4-N than for SRP, yet NH4-N uptake was undetectable during the post-fire period, and SRP uptake was only sporadically detectable. The observed post-fire increase in GPP was strongly associated with a loss in canopy cover. In contrast with these process estimates, we observed similar CO2 and CH4 emissions before and after fire. Our results suggest wildfires can alter the processing and export of materials from tropical watersheds, potentially boosting eutrophication of downstream water bodies. Ongoing climate change has the potential to increase wildfire occurrence worldwide, and our results provide insight into how such increases may alter organic matter dynamics and nutrient processing in tropical streams.