Seaweed biogeochemistry: Global assessment of C:N and C:P ratios and implications for ocean afforestation

[Geoengineering News]

https://onlinelibrary.wiley.com/doi/full/10.1111/jpy.13381

Authors

Emily J. Sheppard, Catriona L. Hurd, Damon D. Britton, Daniel C. Reed, Lennart T. Bach

First published: 19 August 2023

https://doi.org/10.1111/jpy.13381

Editor: M. Roleda

Abstract

Algal carbon-to-nitrogen (C:N) and carbon-to-phosphorus (C:P) ratios are fundamental for understanding many oceanic biogeochemical processes, such as nutrient flux and climate regulation. We synthesized literature data (444 species, >400 locations) and collected original samples from Tasmania, Australia (51 species, 10 locations) to update the global ratios of seaweed carbon-to-nitrogen (C:N) and carbon-to-phosphorus (C:P). The updated global mean molar ratio for seaweed C:N is 20 (ranging from 6 to 123) and for C:P is 801 (ranging from 76 to 4102). The C:N and C:P ratios were significantly influenced by seawater inorganic nutrient concentrations and seasonality. Additionally, C:N ratios varied by phyla. Brown seaweeds (Ochrophyta, Phaeophyceae) had the highest mean C:N of 27.5 (range: 7.6–122.5), followed by green seaweeds (Chlorophyta) of 17.8 (6.2–54.3) and red seaweeds (Rhodophyta) of 14.8 (5.6–77.6). We used the updated C:N and C:P values to compare seaweed tissue stoichiometry with the most recently reported values for plankton community stoichiometry. Our results show that seaweeds have on average 2.8 and 4.0 times higher C:N and C:P than phytoplankton, indicating seaweeds can assimilate more carbon in their biomass for a given amount of nutrient resource. The stoichiometric comparison presented herein is central to the discourse on ocean afforestation (the deliberate replacement of phytoplankton with seaweeds to enhance the ocean biological carbon sink) by contributing to the understanding of the impact of nutrient reallocation from phytoplankton to seaweeds under large-scale seaweed cultivation.

Source: Wiley Online Library

[Michael Hayes]

Cultivation of any biomass on a CDR scale can and likely will use multiple forms of technology. The more confined that the cultivation is, as in using floating bioreactors, one likely will get better MRV numbers and fewer environmental considerations, and possibly larger profits.

Cultivation of seaweed of all types, even many land row crops, can likely be carried out in large marine-grade 'farms' that largely automate the biomass throughput.

To get up to CDR levels using the marine-based biotic path, high throughput cultivation technology will need to be a priority, just as it is with land crops. 

--
You received this message because you are subscribed to the Google Groups "Carbon Dioxide Removal" group.
To unsubscribe from this group and stop receiving emails from it, send an email to CarbonDioxideRem...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/CAHJsh9_MRr8trp4DEbY6DY67AVZCX%3D8dF8wM6vYs%2BqMvbo3Liw%40mail.gmail.com.