Seaweed farming and achieving Net-Zero

Environmental Life Cycle Assessment (LCA) is a method that can be used to evaluate the overall environmental sustainability of seaweed farming and its supply chains. LCA’s include calculations on carbon uptake and emissions of a product, activity, or process over its entire life cycle. Scientists recently carried out an LCA for the cultivation and preservation of kelp in Northern Europe, and reported that more CO2 was absorbed by the farmed kelp than emitted by the supply chain, but that processing method had a big impact on total emissions (Thomas et al., 2021). Their cultivation and processing systems are very similar to our own, and the science was rigorous, so this is the best set of data for us to use right now. Their findings are summarised below:

For every 1 ton freshly harvested kelp biomass, 39.6 kg of carbon is captured, corresponding to the mitigation of 145 kg of CO2 equivalent.

• The cultivation process (from seed to harvest) results in emissions of around 55.2 kg of CO2 equivalent per 1 ton of kelp biomass grown.

• After harvest, seaweed is processed in various ways, such as drying, freezing, ensiling or fermenting (which involves adding acids or bacteria to seaweed to lower the pH and preserve it). Depending on which processing method is used, this results in average emissions of 40.8 kg CO2 for cabinet drying, 18.2 kg CO2 for ensiling and 92.5 kg CO2 for freezing (per wet ton kelp processed).

• If you subtract the cultivation and processing emissions from the CO2 captured per ton of harvested kelp, then it is clear to see that kelp farming is generally carbon negative or close to carbon neutral, and ensiling kelp has the lowest emissions (and freezing the highest).

At KelpCrofters we are moving towards wet-processing and ensiling our seaweed (less or no drying and freezing) so we can be carbon negative. We also have solar panels which entirely offset electricity used in the hatchery stage, and are investing in low-energy drying methods. Its important to highlight that these net negative emissions are temporary, and we should also consider what happens to a seaweed product after it leaves the factory (as discussed by Hasselstrom, L., and Thomas, J-B, 2022). If the seaweed is used for human food, the carbon stored in the seaweed will be returned to the environment after only a short period of time (0-10 years) when food is eaten and metabolised, releasing CO2. If the seaweed is turned into plant feeds and bio-fertilisers this will boosts plant growth, which leads to additional absorption of CO2 by plants, and draws carbon down into the soil through the process of root formation. This enhances the climate benefits of seaweed products, and removes some reliance on chemical fertilisers in agriculture, which are one of the major sources of greenhouse gas emissions.

References:

Thomas J-B., et al. (2021) A comparative environmental life cycle assessment of hatchery, cultivation, and preservation of the kelp Saccharina latissima. ICES Journal of Marine Science, 78(1), 451–467.

Hasselstrom, L., and Thomas, J-B. (2022). A critical review of the life cycle climate impact in seaweed value chains to support carbon accounting and blue carbon financing. Cleaner Environmental Systems (2022).100093