Wildfires produce phosphorus-rich ash which can alter light and nutrient availability in lakes, ultimately influencing ecosystem processes such as primary production or biogeochemical cycles. However, the immediate effects of wildfire-derived nutrients on lake ecosystems are unclear, particularly in grasslands which are understudied in the context of wildfire:lake interactions. In this study we used bottle bioassays and a process-based model to determine how ash concentrations of 0-100 ppm influenced primary production and nutrient limitation in productive grassland lakes in Western Nebraska. We hypothesized that ash-derived phosphorus would initially increase primary production but eventually shift lakes towards light or nitrogen limitation. Our approaches produced mixed results: although ash increased phosphorus availability in the bottle bioassays, pervasive nitrogen limitation constrained primary production. In contrast, ash inputs increased primary production and shifted lakes towards light- followed by nitrogen-limitation in the process-based model. For both the bioassays and process-based model, the effect of ash on lake on primary production and nutrient cycling was modified by the availability of nitrogen, indicating stoichiometric constraints on lake ecosystem processes. Our results suggest that the effects of wildfires on lake ecosystems are mediated by trophic state and nutrient stoichiometry.

Authors:

Daniel Gschwentner, University of Nebraska Lincoln  (dgschwentner2@huskers.unl.edu)

Jessica Corman, University of Nebraska Lincoln  (jcorman3@unl.edu)