Coastal plankton response to fire-ash leachate shaped by pre-existing in situ conditions

Climate-driven warming is projected to increase the magnitude and severity of wildfires, as well as the frequency of severe wildfires, in many regions around the world. Wildfire ash deposition can be a source of essential new nutrients for phytoplankton in the ocean, but ash can have variable nutrient content and can carry heavy metal and organic matter toxins that inhibit microbial growth. Here we quantitatively describe short-term physiological and ecological responses of coastal surface ocean microbial groups to the compounds leached from fire-ash, collected from the 2017 Thomas Fire in California and produced in the lab from coastal Oregon foliage. We find that the microbial impacts of fire-ash leachate may depend less on its composition and more on the pre-existing in situ conditions and microbial community. Dissolved organic matter (DOM) from fire-ash leachate could stimulate bacterial production, but its bioavailability to bacteria was observed to decrease in high biomass conditions. Additionally, zooplankton grazing rates decreased more than phytoplankton division rates in response to fire-ash leachate, both in low and high biomass conditions. This led to increased phytoplankton accumulation rates, which could set the stage for large-scale blooms.

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Primary Presenter: Nicholas Baetge, Oregon State University (nicholasbaetge@gmail.com)

Authors:

Kimberly Halsey, Oregon State University  (Kimberly.Halsey@oregonstate.edu)

Erin Hanan, University of Nevada, Reno  (ehanan@unr.edu)

Michael Behrenfeld, Oregon State University  (Michael.Behrenfeld@oregonstate.edu)

Allen Milligan, Oregon State University  (Allen.Milligan@oregonstate.edu)

Jason Graff, Oregon State University  (jrgraff@science.oregonstate.edu)

Parker Hansen, Oregon State University  (parker.hansen@oregonstate.edu)

Craig Carlson, University of California Santa Barbara  (carlson@lifesci.ucsb.edu)

Rene Boiteau, University of Minnesota  (rboiteau@umn.edu)

Eleanor Arrington, University of California Santa Barbara  (earrington@ucsb.edu)

Jacqueline Comstock, University of California Santa Barbara  (jacquicomstock@gmail.com)

Elisa Halewood, University of California Santa Barbara  (wallner@ucsb.edu)

Elizabeth Harvey, University of New Hampshire  (elizabeth.harvey@unh.edu)

Norm Nelson, University of California Santa Barbara  (norm@eri.ucsb.edu)

Keri Opalk, University of California Santa Barbara  (keri.opalk@ucsb.edu)

Brian Ver Wey, Oregon State University  (Brian.Verwey@oregonstate.edu)