UC Irvine

The combustion of fuels in the engines of ships releases inorganic compounds and metals that can promote phytoplankton growth (e.g. N, Fe, Mn, Zn) or decrease productivity (e.g. Cu). Many ship operators comply with air quality regulations by installing scrubber systems that clean emissions going into the air, but discharge washwater containing nutrients and contaminants directly into ocean water. This has the potential to change primary production rates and the structure of phytoplankton populations. Chapter 1 of the dissertation analyzed scrubber washwater samples from small engines combusting distilled fuels. Results revealed consistent enrichment of washwater with nitrogen and dissolved trace metals, with variations in the specific metals enriched. I compared our results to those found in the literature for a distilled fuel that was combusted in a small engine, and for residual fuels combusted in large ship engines. Using diverse model simulations, Chapter 1 demonstrated that cumulative scrubber water discharges could fertilize phytoplankton in specific regions by providing essential nutrients like iron. In Chapter 2, I presented results from mesocosm experiments simulating acute exposure of coastal phytoplankton to high concentrations (1%, 5%, and 10%) of scrubber washwater from engines using both distilled and residual fuels. Growth responses varied across phytoplankton taxa and fuel types, providing insights into potential ecological consequences in heavily trafficked coastal regions. Chapter 3 explored the impact of scrubber washwater discharges on natural phytoplankton communities in the Sargasso Sea. Both conventional heavy fuel oil (HFO) and alternative distilled fuel (HGO) exhibited mild fertilizing effects at a 2% concentration. This chapter emphasized co-limitation by multiple nutrients, with scrubber washwater at 2% adequately supplying nutrients compared to lower concentrations. This dissertation highlights the complex interactions between ship emissions, scrubber washwater, and marine ecosystems, emphasizing the need for comprehensive assessments to inform sustainable maritime practices.