03 Jan 2022
03 Jan 2022
Status: this preprint is currently under review for the journal BG.

Investigating the effect of nickel concentration on phytoplankton growth to inform the assessment of ocean alkalinity enhancement

Jiaying Abby Guo1, Robert Strzepek2, Anusuya Willis3, Aaron Ferderer1, and Lennart Thomas Bach1 Jiaying Abby Guo et al.
  • 1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
  • 2Australian Antarctic Program Partnership (AAPP), Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
  • 3National Collections and Marine Infrastructure, Commonwealth Scientific and Industrial Research Organisation, Hobart, Tasmania, Australia

Abstract. Ocean alkalinity enhancement (OAE) is a proposed method for removing carbon dioxide (CO2) from the atmosphere by the accelerated weathering of (ultra-) basic minerals to increase alkalinity – the chemical capacity of seawater to store CO2. During the weathering of OAE-relevant minerals relatively large amounts of trace metals will be released and may perturb pelagic ecosystems. Nickel (Ni) is of particular concern as it is abundant in olivine, one of the most widely considered minerals for OAE. However, so far there is limited knowledge about the impact of Ni on marine biota including phytoplankton. To fill this knowledge gap, this study tested the growth and photo-physiological response of 11 marine phytoplankton species to a wide range of dissolved Ni concentrations (from 0 nmol/L to 50,000 nmol/L). We found that the phytoplankton species were not very sensitive to Ni concentrations under the culturing conditions established in our experiments, but the responses were species-specific. The growth rates of 6 of the 11 tested species showed small but significant responses to changing Ni concentrations. Photosynthetic performance, assessed by measuring the maximum quantum yield (Fv/Fm) and the functional absorption cross-section (σPSII) of photosystem II, was also only mildly sensitive to changing Ni in 3 out of 11 species and 4 out of 11 species, respectively. The limited effect of Ni may be partly due to the provision of nitrate as the nitrogen source for growth, as previous studies suggest higher sensitivities when urea is the nitrogen source. Furthermore, limited influence may be due to the relatively high concentrations of organic ligands in the growth media in our experiments. These ligands reduced bioavailable Ni (i.e., “free Ni2+”) concentrations by binding the majority of the dissolved Ni. Our data suggest that dissolved Ni does not have a strong effect on phytoplankton under our experimental conditions, but we emphasize that a deeper understanding of nitrogen sources, ligand concentrations and phytoplankton composition is needed when assessing the influence of Ni release associated with OAE. We discuss if applications of OAE with Ni-rich minerals may be safer in regions with high organic ligand concentrations and low concentrations of urea as such boundary conditions may lead to less impact of Ni on phytoplankton communities.

Jiaying Abby Guo et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on bg-2021-312', Zuzi Koscikova, 07 Feb 2022
    • AC3: 'Reply on CC1', Jiaying Guo, 02 Jun 2022
  • RC1: 'Comment on bg-2021-312', Anonymous Referee #3, 12 Apr 2022
    • AC1: 'Reply on RC1', Jiaying Guo, 02 Jun 2022
  • RC2: 'Comment on bg-2021-312', Anonymous Referee #4, 26 Apr 2022
    • AC2: 'Reply on RC2', Jiaying Guo, 02 Jun 2022

Jiaying Abby Guo et al.

Jiaying Abby Guo et al.


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Short summary
Ocean alkalinity enhancement is a carbon removal method, but it may cause a significant perturbation of the ocean with trace metals such as Nickel (Ni). This study tested the effect of increasing Ni concentrations on phytoplankton growth and photosynthesis. We found that the response to Ni varied across the 11 phytoplankton species tested here but the majority were insensitive. This may be due to the use of nitrate as the nitrogen source and due to high ligand concentrations (low Ni2+) in media.