Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • BCO-DMO Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

All surface seawater was collected just prior to local sunrise from a SBE-911+ Conductivity-Temperature-Depth (CTD, Sea-Bird Scientific) Niskin bottle rosette cast and then transferred or directly filtered into acid-cleaned 20-liter (L) carboys with platinum-cured silicone tubing.

Bacterial growth and dissolved organic carbon (DOC) utilization were estimated in six microbial remineralization experiments following Baetge et al (2021), in which changes in bacterioplankton cell densities, bacterial organic carbon, and TOC were measured over five day incubations. For each experiment, 3-micrometer (µm) filtered surface seawater was directly and gently gravity-filtered through a mixed cellulose ester (MCE) membrane filter (EMD Millipore, 142-millimeters (mm)) in a polycarbonate filtration cartridge (Geotech Environmental Equipment, Inc.) with platinum-cured silicone tubing. The filtrate was then filtered through a 1.2- or a 0.2-µm MCE filter (EMD Millipore, 142 mm) to generate a bacterial inoculum or DOC media, respectively. Experiments were initiated when filtrates were mixed in a ratio of 1:4 bacterial inoculum to DOC media. Mixed seawater either remained unamended or was amended with ash leachate prior to being divided into a modified acid-washed 5 L polycarbonate bottle (Biotainer, Nalgene) (Baetge et al., 2021) and a set of 18 pre-combusted 40-milliliter (ml) EPA vials. Ash leachate DOC was added to experimental treatments at a final amendment concentration of ~4 µmol C/L Bottles and vials were incubated in the dark within ± 2 degrees Celsius (C) of in situ temperatures using wine coolers (YEG-2WS24-HD, YEEGO).

For each experiment, 2 ml samples for bacterial abundance were collected daily from all incubations. Triplicate 40 ml EPA vials were preserved daily as total organic carbon (TOC )samples after acidification to a pH of < 3 with 4 N HCl. Bacterial organic carbon (BOC) samples were collected in triplicate 1 L polycarbonate bottles from the bacterial inoculum and as samples from the 5 L polycarbonate bottles on the second and fifth days of the experiment. Bacterioplankton abundance (cells/L) samples were fixed upon collection with paraformaldehyde to a final concentration of 1%, flash-frozen in liquid nitrogen, and stored at -20 degrees C. Sample volumes for BOC (micromoles C per liter (µmol C/L)) measurements were filtered through two stacked pre-combusted 0.3 µm GF/75 filters (25 mm, Advantec) in inline polypropylene cartridges (Cole-Parmer). At three experimental sites, DOC media (i.e., 0.2 µm filtrate) was also filtered to generate triplicate background correction samples to account for DOC filter adsorption (Graff et al., 2023). All filters were stored in pre-combusted 20 ml borosilicate glass vials (Wheaton) at -20 degrees C, and then later fumed for 24 hours with HCl and dried for 24 hours at 50 degrees C prior to analysis.

- Imported original file "BACTERIA_DOM.csv" into the BCO-DMO system.
- Flagged "NA" as a missing data value; missing data are empty/blank in the final CSV file.
- PI applied rounding to numeric values and provided a new file.
- Saved final data file as "953702_v1_dom_remineralization_bioassays.csv".

NSF Award Abstract:
Climate-driven warming is projected to increase the frequency, intensity, and size of wildfires that can have severe environmental, human, and economic impacts, particularly along the U.S. West Coast. These wildfires result in dramatic CO2 emissions and deposition of ash carrying nutrients, organic matter, and trace metals onto the coastal and open ocean. Deposition of wildfire ash on the ocean can alter the carbon and energy flow through marine food webs by fertilizing microbial production or inhibiting microbial growth due to heavy metal toxicity. How the character of both the ash (e.g., chemical quality, fertilizing v. toxic) and the starting microbial community composition (e.g., diversity, size distribution) influences the microbial response to ash-derived material is unknown. This project will address this knowledge gap by investigating the physiological responses of marine plankton off the U.S West Coast to different types of ash generated from local wildfires and plant biomass. This work will advance interdisciplinary science, bridging biological oceanography with terrestrial ecology and biogeochemistry, by generating foundational knowledge of wildfire impacts on surface ocean biology and carbon and energy transfer from land to ocean. Results from this project will enable improved forecasts of changes in marine ecosystems in response to wildfires, which is information pertinent to communities and industries that depend on ocean ecosystem resources, including fisheries. The work will also inform national efforts to mitigate and adapt to the impacts of climate change by addressing whether wildfire-stimulated fertilization and carbon fixation in the ocean can offset CO2 emissions from wildfires. This project will broaden participation and education in ocean science by providing immersive research experiences for multiple undergraduate students and opportunities for them to disseminate their work through scientific conferences and publications. Additionally, a day-long content unit related to the project will be developed and implemented in Oregon State University’s annual week-long Microbiology Summer Camp, which provides local high school students with a hands-on learning experience in microbiology.

Specifically, this project consists of mechanistic studies designed to quantitatively describe the physiological responses (e.g., growth, productivity, cellular stoichiometry) of phytoplankton and bacterioplankton to a variety of ash types. The quantity and proportion of nutrients, organic matter, and trace metals leached from ash into seawater likely depends on the quality of the ash, which is influenced by vegetation type and the temperature at which the ash was produced. This study will assess how microbial production and growth are fertilized or inhibited by the composition of ash and will consist of two primary elements. In the first element, ash will be collected from the field and generated in the lab from plant biomass. The ash will then be leached in seawater and chemically characterized for inorganic and organic matter content. In the second element, seawater incubation experiments will be conducted to quantify physiological and diversity-based responses of naturally occurring phytoplankton and bacterial communities to different ash types. Data generated from this project will contribute to improved predictive models of wildfire-driven material transfer from the terrestrial system to the ocean and its impact on carbon and energy flow in marine food webs.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.