Katherine Bowen

Document Type

Honors Thesis

Major

Marine Science

Advisor(s)

Lee Karp-Boss

Committee Members

Jeremy Rich, Benjamin Twining, Mark Wells

Graduation Year

May 2024

Publication Date

2025

Abstract

Iron is an important and often limiting nutrient to phytoplankton growth. However, a large portion of iron in the ocean is also associated with inorganic particles. Consequently, it is essential to determine the fraction of iron that is associated with phytoplankton, which is often accomplished with an acetic acid (HAc) chemical leach developed to solubilize only the labile fraction of elements. This biological fraction needs to be normalized to phytoplankton biomass, for which phosphorus is typically used. The goal of this study was to determine what fraction of phytoplankton phosphorus is recovered by the HAc leach. The diatom Phaeodactylum tricornutum and the haptophyte Isochrysis galbana were grown in media with varying iron and silica availability. Phytoplankton phosphorus solubilized with HAc were compared to total phosphorus levels determined with a strong acid digest. Phosphorus lability to the HAc leach was lower than expected, particularly in the diatoms, from which only around 50% of phosphorus was recovered. Silica and iron treatments suggested that the diatom frustule and external Fe adsorption likely has little impact on the lability of phosphorus. Species comparison indicated that the HAc digestion may be species dependent. Overall, the HAc digestion protocol may not recover all phosphorus associated with biological particles, particularly in communities with diatoms.

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