The impact of future environmental change on benthic ecosystem functioning and Carbon cycling in UK shelf seas

Marine sediments are considered to be one of the largest carbon reservoirs in the world and play an important role in climate regulation. It is essential that there is a better understanding of the distribution, sources, lability, and vulnerability to degradation of carbon within shelf sea sediments. This will aid the improved management of carbon storage as an ecosystem service, especially considering predicted future environmental change, such as ocean warming. Therefore, it is also essential that a better understanding is gained on how intact benthic communities will respond to predicted environmental changes (e.g. temperature rises). Research was undertaken using both an observational approach using a spatially distributed dataset and using a manipulative experiment looking in detail at benthic ecosystem function. This thesis demonstrates that temperature influences biodiversity and ecosystem function (BEF) relationships, especially the uptake and processing of organic carbon entering the benthic environment. This research indicated that temperature rises resulted in a higher sediment community oxygen uptake, higher amount of bioirrigation and more organic carbon was respired releasing more carbon dioxide. The results also indicate that it is possible that the functional structure of benthic communities could shift in the future due to temperature increases. This research also demonstrated that the distribution, lability, and vulnerability of carbon within shelf sediments can be complex over relatively small spatial scales. This research indicates that in the northern North Sea more organic carbon exists in sediments found further offshore compared to sediments found closer to the coastline. However, an amino acid based degradation index indicates that this organic carbon found further offshore is more degraded in comparison to sediment found nearer the coastline. This suggests that shelf sediments found nearer the coastline are potentially more vulnerable to degradation than sediments found further away from the coastline. This information can inform more detailed and targeted management strategies for shelf sea sediments which regard to carbon storage. This research examines the impact that future ocean warming could have on the functioning, specifically carbon cycling and storage, of marine benthic environments. This thesis also highlights the need to better understand the composition and reactivity of carbon in marine sediments to better inform management of the marine environment, and better predict the impact that future environmental change could have on marine sedimentary carbon storage.