Lack of impact of ocean alkalinization enhancement in coastal heterotrophic bacteria communities of the Canary Region

Abstract

In contrast to acidification, Ocean Alkalinity Enhancement (OAE) entails the augmentation of bicarbonate ion concentration in the oceanic water column. This technology has the potential to serve as a Negative Emission Technology (NET) for the mitigation of climate change. In addition to enhancing long-term carbon storage, the OAE has the potential to counteract ocean acidification. However, it is possible that this process may also affect the availability of essential inorganic nutrients and dissolved organic carbon, which are crucial elements for bacterial growth and metabolism in the oceans. The objective of this study was to analyze the impact of ocean alkalinity enhancement on the evolution of bacterial communities, specifically high nucleic acid (HNA) and low nucleic acid (LNA) heterotrophic bacteria, as well as changes in dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and their optical properties (CDOM), in response to different alkalinity concentration scenarios in the environment. To this end, a series of nine TA levels were established in a mesocosms experiment and maintained for 33 days. No TA effects were observed in either the HB abundances or community structure. Furthermore, the dynamics of dissolved organic matter were not impacted by TA or by increases in bacterial abundances. The lack of impact of HB on organic matter dynamics suggests that viral lysis could play an important role in enhancing the pool of DOC under OAE. However, this should be considered a preliminary hypothesis that requires further validation through additional studies.