Composition of Laminaria digitata biomass during a potential

Emissions from fossil fuels and a change of land use are two of the main contributors to climate change and thereby threatens our health and well-being. Finding new sources of materials for production of fuels, food and commodities are of high importance. Biomass from plants and photosynthetic organisms is a potential solution, and algae is one type of organisms under investigation today. The interest in brown macroalgae, seaweeds, has increased in recent years, as they contain carbohydrates that can be converted into fuels as well as nutritional substances. Seaweed has advantages from having the ocean as its natural habitat, thereby not requiring freshwater or agricultural lands. They also require milder processing conditions compared to terrestrial biomass sources. The composition in seaweeds varies with the seasons and environmental conditions. The potential of seaweed biomass is determined by the composition, and thereby knowledge of the variations between seasons is crucial to determining the optimal harvesting time, which was the aim of this project. The project was performed using samples of the brown seaweed Laminaria digitata collected from three different locations in Kosterhavet National Park on the Swedish West Coast in June, August and October. Samples were analyzed for compositional variations in carbohydrates and elemental content. Laminaria digitata was found to contain high amounts of carbohydrates ranging between 34 and 55 % of the dry weight (excluding one of the major carbohydrates, alginate). The elemental components carbon, hydrogen, nitrogen and sulphur ranged between 34.5-38.5, 4.9-5.55, 1.09-2.34 and 1.24-1.60 % respectively. Proteins estimated from the nitrogen content were 5-12 % of dry weight. Mannitol and protein content showed the hypothesized seasonal fluctuations, both with peaking values in autumn, while the remaining carbohydrates did not show these. The variations between plants collected at the same site and month where high and to some extent confounded the hypothesized seasonal variations. Seasonal variations in the total carbohydrate content showed no consistent trends between sites, nor where there any considerable variations within the sites. Thus, a conclusion of the optimal harvesting season should be drawn based on size of the plants as well as fouling. Harvest in spring was concluded to be optimal