Investigating the effect of nickel concentration on phytoplankton growth to assess potential side-effects of ocean alkalinity enhancement

[摘要] Ocean alkalinity enhancement (OAE) is a proposed method forremoving carbon dioxide (CO 2 ) from the atmosphere by the acceleratedweathering of (ultra-)basic minerals to increase alkalinity – the chemicalcapacity of seawater to store CO 2 . During the weathering ofOAE-relevant minerals relatively large amounts of trace metals will bereleased and may perturb pelagic ecosystems. Nickel (Ni) is of particularconcern as it is abundant in olivine, one of the most widely consideredminerals for OAE. However, so far there is limited knowledge about theimpact of Ni on marine biota including phytoplankton. To fill this knowledgegap, this study tested the growth and photo-physiological response of 11marine phytoplankton species to a wide range of dissolved Ni concentrations(from 0.07 to 50 000 nmol L −1 ). We found that the phytoplankton specieswere not very sensitive to Ni concentrations under the culturing conditionsestablished in our experiments, but the responses were species-specific. Thegrowth rates of 6 of the 11 tested species showed generally limited butstill significant responses to changing Ni concentrations (36 % maximumchange). Photosynthetic performance, assessed by measuring the maximumquantum yield ( F v / F m ) and the functional absorption cross-section( σ PSII ) of photosystem II (PSII), was sensitive to changing Ni in 3out of 11 species (35 % maximum change) and 4 out of 11 species (16 %maximum change), respectively. The limited effect of Ni may be partly due tothe provision of nitrate as the nitrogen source for growth as previousstudies suggest higher sensitivities when urea is the nitrogen source.Furthermore, the limited influence may be due to the relatively highconcentrations of synthetic organic ligands added to the growth media in ourexperiments. These ligands are commonly added to control trace metalbioavailability and therefore for example “free Ni 2+ ” concentrationsby binding the majority of the dissolved Ni. Our data suggest that dissolvedNi does not have a strong effect on phytoplankton under our experimentalconditions, but we emphasize that a deeper understanding of nitrogensources, ligand concentrations, and phytoplankton composition is needed whenassessing the influence of Ni release associated with OAE.

[学科分类] 大气科学