There is a growing interest in the role of seaweeds in absorbing carbon and exporting part of this to “Blue Carbon” sinks during cultivation as particulate or dissolved organic carbon - POC and DOC, respectively. However, the potential for carbon sequestration from seaweed farms remains largely unknown and un-quantified. The PhD project will collect data simultaneously from cultivated Saccharina latissima on carbon uptake, growth and erosion, as well as losses of larger fragments, DOC production and fate in a combination of field and lab experiments. Applications for industry such as carbon credits and multi-market opportunities will also be assessed in practical terms.
Year two activities and further plans:
Two main field experiments and one main laboratory experiment took place in 2022.
A multi-crop experiment was completed at SINTEF Ocean’s new seaweed site in Skarvøya, Hitra, demonstrating a rapid recovery post-cropping and yield improvement over the season. The resulting biomass from the different harvest times may cater for both high-value-low-volume markets such as food, feed, biochemicals, etc., as well as a potential future carbon market for the high-volume-low-value seaweed. The first year of investigations on erosion dynamics, including differences between October- and January- deployed seedlings of S. latissima, was completed, and a second season of data will be gathered in 2023. In parallel, a small in-situ incubation experiment will be carried out to monitor initial DOC release (24hrs) from the two deployments, twice in the year. Together, we hope to fill knowledge gaps about the “unseen production” which grows and is lost at seaweed farms between deployment and harvest times to both POC and DOC pools.
Freshly cultivated S. latissima were harvested in Hitra in May and used in a mesocosm experiment at TBS, Trondheim, to investigate the production (over 4 days) and degradation (over 188 days) of macroalgae POC and DOC. Incubation bags of 20L were used with and without seaweeds, in daylight and dark treatments, sampled ‘destructively’ over 4 days. The biodegradation study was then performed under two temperatures, 4 and 10?C. Samples were collected at 0, 5, 15, 30, 60, 94, 154, 188 days for a range of analysis types, including POC, DOC, TOC concentrations, inorganic nutrients, dissolved inorganic carbon (DIC), pH, dissolved oxygen (DO) and temperature. Samples were also collected for bacterial community assessment from both seaweed tissue and water samples, along with DOC characterization samples over the course of the experiment, to provide information on the breakdown of DOC from labile and semi-labile carbon into more refractory forms (and the bacteria involved in the process). Sample analysis is ongoing, and we aim to involve international collaboration on characterization analysis with FT-ICR-MS and/or ORBITRAP. To complete the lab trials from 2022 and further explore the refractory components of macroalgae-DOC in a real case scenario, water samples will be taken from inside and outside a large seaweed farm in Frøya, from Seaweed Solutions AS (SES), twice during the 2023 season.
Two MSc students have been involved in the work from 2022, due to be completed in Q2 of 2023.