Assessing the Impacts of Simulated Ocean Alkalinity Enhancement on Viability and Growth of Cultures of Near-Shore Species of Phytoplankton

Abstract

Over the past 250 years, atmospheric carbon dioxide concentrations have risen steadily from 277 ppm to 405 ppm, leading to the exacerbation of the effects of climate change. As a result, new technologies are being developed to remove carbon from the atmosphere, such as negative emission technologies (NETs). One proposed NET is Ocean Alkalinity Enhancement (OAE), which would mimic the ocean’s natural weathering processes and sequester carbon dioxide from the atmosphere. An analysis of published data investigating the effects of elevated pH on phytoplankton growth rate and experimental assessment of pH dependence of viability and growth rate was used to assess the potential impacts of OAE. Viability was assessed with a modified Serial Dilution Culture – Most Probable Number assay. Chlorophyll a fluorescence was used to test for changes in growth rates and photosynthetic competence. The results from this study suggest that there will be no significant impact on the viability or growth rates of Thalassiosira pseudonana or Pavlova lutheri with short-term (10 minute) exposure to elevated pH. However, when long-term (days) exposure occurs there is a significant decrease in growth rates with elevated pH. Short-term exposure is anticipated to more closely mirror the natural systems in which OAE will be implemented because of system flushing and replenishment of nutrients. These preliminary findings suggest that there will be little to no impact on a variety of taxonomic groups of phytoplankton when OAE occurs in naturally flushed systems.