I tested the potential impacts of Ocean Alkalinity Enhancement (OAE) on phytoplankton in a mesocosm study. To restrict warming to the 1.5-degree target, we must now rely on carbon dioxide removal strategies (IPCC 2022) such as OAE. I deployed six mesocosms in the Bedford Basin, the pilot site for this technology, with three duplicated treatments: a control, and alkaline treatments with 50 uM and 500 uM magnesium hydroxide additions. These correspond to target and 10x target concentrations for OAE and resulted in changes of 0.3 and 0.8 pH units, respectively. Incubations lasted 24 hours to represent the effect of alkalization before dilution by water flow. Mesocosms were sampled before and after the addition of alkalinity and again on harvest. Physicochemical parameters, including particulate and dissolved carbon pools, were measured; phytoplankton community composition and abundance were assessed by flow cytometry and chlorophyll-a content. Statistical tests for treatment effects on population structure and chlorophyll-specific growth rates were tested using analysis of similarity (ANOSIM) and analysis of variance (ANOVA), respectively. At harvest, there was no significant difference in community composition between treatments (p=0.13) nor between chlorophyll-specific growth rates (p=0.26). There were significant differences (p<0.05) in both community composition between the start and end of the experiment. This study is an important first step in assessing the potential impact of OAE and demonstrates that it can be undetectable.

Primary Presenter: Mikaela Ermanovics, Dalhousie University (mk667000@dal.ca)

Authors:

Mikaela Ermanovics, Dalhousie University   (Mikaela.Ermanovics@dal.ca)

Jessica Oberlander, Dalhousie University  (Jessica.Oberlander@dal.ca)

Cat London, Dalhousie University  (Cat.London@dal.ca)

Marie Egert, Dalhousie University  (mr594601@dal.ca)

Meghan Oliver, Dalhousie University  (MeghanOliver@dal.ca)

Brenan Duhamel, Planetary Technologies  (Brenan@planetarytech.com)

Nicole Neriuoka, Dalhousie University  (nc217923@dal.ca)

Hugh MacIntyre, Dalhousie University  (Hugh.Macintyre@dal.ca)