Biogeochemical assessment of English kelp ecosystems: baseline data for the Environment Agency’s national kelp monitoring programme

This study has created a comprehensive dataset on the carbon-to-nitrogen (C:N) ratios of key kelp species in the UK, particularly within the seaweed aquaculture sector. It highlights knowledge gaps in seaweed stoichiometry and its links to environmental variables, as well as species-specific and spatiotemporal variations. The study evaluates nutrient uptake in four kelp species: Saccharina latissima, Laminaria hyperborea, Laminaria digitata, and Alaria esculenta and monitors nitrogen pollution sources in coastal areas through nitrogen isotope analysis. In traditional methodology on seaweed’s stable isotopes and stoichiometry only a section of tissue is removed for the whole specimen. However, in this study due to potential internal variation along the blade, samples were taken incrementally along the middle ridge of the blade for A. esculenta, along the centre of the blade for S. latitssima, and every 2 cm along the central blade for L. hyperborea and L. digitata. The analysis shows significant variation (p <.001) in carbon-to-nitrogen (C:N) ratios among kelp samples, with kelp having a C:N ratio of 24.1. Laminaria hyperborea consistently shows higher C:N ratios than other species. Carbon assimilation in kelp could be primarily influenced by species type rather than location. However, both factors significantly correlate with nutrient assimilation, highlighting the need to consider them in assessments of kelp nutrition. Isotope nitrogen values differ across sites and species, highlighting the influence of factors like nitrogen type preference and environmental conditions on nitrogen pollution monitoring. While most kelp samples show natural δ15N values, it is interesting to see that when comparing site locations, six sites indicate pollution from sources like sewage and fertilisers (Fig. 12). Further investigation is needed to understand the combined effects of these variables on δ15N levels. Further research comparing these species throughout their growing season is essential to understand nutrient dynamics. It is also important to investigate the variation of nutrients along the lamina to assess nutrient limitations. Additionally, examining the bioremediation effects of kelp farms in specific areas of the UK, such as the Mersey Estuary, could contribute valuable insights to research on coastal water quality.