Assessing the impact of environmental pressures on seagrass Blue Carbon stocks in the British Isles

• Main Author: Green, Alix Evelyn
• Format: Dissertation
• Language: English
• Published: UCL (University College London) 2020

The requirements of nations to respond to the Paris Climate Agreement by outlining National Determined Contributions (NDC’s) to reduce their emissions is placing an increased global focus on the spatial extent, loss and restoration of seagrass meadows. Despite such interest, local carbon storage trends and the spatial extent of seagrass remains poorly mapped globally, and knowledge of historical loss is limited. In the British Isles this information is largely absent. The primary aim of this work was to provide a foundation of knowledge on seagrass Blue Carbon and the status of seagrass in the British Isles, to 1) better inform local conservation and management, and 2) further advance the field’s understanding of trends in sediment carbon storage. The work raised questions about the globally accepted standards for Blue Carbon research, particularly in extrapolating estimates from short (<40cm) to long (>100cm) cores. This underestimated carbon stocks by >40% in one site. Across 13 studied seagrass meadows, seagrass carbon stocks were similar, apart from at one anomalous site, and differences could not be explained by sediment silt content or aboveground biomass. Despite local similarities, on a European scale the average recorded carbon stocks were high, representing the second most carbon dense sediment per hectare of any documented European country. I found that seagrass sediments disturbed by anchoring and mooring activates had significantly less sediment carbon than undisturbed seagrass sediment. Finally, I documented 8,493 ha of recently mapped seagrass in the British Isles. With high certainty, 41% of British seagrass has been lost since 1936, and historic seagrass losses could be as high as 92%. The results are discussed in terms of conservation and management of seagrass, particularly pertaining to Blue Carbon provisions.