Summarized by Devin Buss, Roy Little Fellow
To understand how post-wildfire run-off threatens freshwater quality and aquatic food webs, UC San Diego masters student Cody Spiegel, post doctoral scholar Christopher Wall, and professor Jonathan Shurin, as well as researchers from UC Irvine and San Diego State University, investigated how burned versus unburned plant matter alters dissolved carbon in local streams. To replicate field conditions, the team collected native arroyo willow, Salix lasiolepis, along Agua Hedionda Creek at UC San Diego’s Dawson Los Monos Canyon Reserve. Willows were chosen because they are dominant, fire-vulnerable plants in Southern California's seasonally dry streamside habitats.
The harvested plants were dried and sorted into unburned, low-severity burn, and high-severity burn treatments before being added across a range of quantities to 400-liter experimental ponds, called mesocosms. Researchers found that the plant material that was unburned released large amounts of carbon in pulses. The sudden entry of carbon caused an intense microbial respiration increase which depleted the oxygen in the water creating a hypoxic environment. This made the water uninhabitable for many aquatic species. Despite this, the remaining microorganisms were very efficient at using new carbon sources which completely changed the microbial composition and freshwater ecosystem functions. The findings from this paper not only emphasize that carbon cycling is altered, but it also changes the food web and causes a cascade through an ecosystem’s functions.
Find the UC San Diego Today write up of this and a related study here: https://today.ucsd.edu/story/wildfires-also-impact-aquatic-ecosystems
Find the full paper here: Spiegel, C. J., Mladenov, N., Wall, C. B., Hollman, K., Tran, C. H., Symons, C. C., & Shurin, J. B. (2024). Life after a fiery death: Fire and plant biomass loading affect dissolved organic matter in experimental ponds. Global Change Biology, 30(1), e17061.
