Coastal zones are hotspots for biogeochemical cycling, playing a globally-important role in the Earth System and underpinning diverse societal and ecological services. Coastal sediments are highly efficient bioreactors, mineralising carbon, recycling nutrients and controlling primary production. However, coastal processes can also drive negative outcomes e.g. the production of algal blooms and low oxygen conditions, with detrimental impacts for coastal ecosystems.
Despite the importance of this part of the ocean, the environmental controls on the consumption, production and conversion of nutrients and other solutes in coastal, often sandy (permeable), sediments remain poorly understood1,2. This uncertainty arises from a paucity of direct measurements in the upper centimetre-decimetre of coastal sediments, which often feature very steep geochemical gradients. Direct measurements have not been possible previously due to a lack of in-situ sensors for many biogeochemical species. However, new Lab-on-Chip sensors3 provide analytical capabilities to finally resolve geochemical processes and provide a much-needed step change in coastal sediment understanding. This project will develop and test novel methods using for the first time Lab-on-Chip sensors to quantify nutrient gradients and fluxes in permeable sediments and will transform our understanding of critical biogeochemical processes across coastal zones.
The Lab-on-Chip sensors, developed at the National Oceanography Centre, implement standard laboratory assays on an automated microfluidic hardware platform. These sensors have already been deployed in marine waters for up to a year and are uniquely poised to offer analytical capability directly in the seafloor in near-real time.
To use these sensors for measurements in marine sediments, it is required to first develop novel methods to use sensors to analyse sediment porewater composition and/or characterise benthic fluxes, and to then test, verify and improve these methods in a controlled laboratory environment. To assess the denitrification capacity of coastal sediments and their potential to counteract the anthropogenic nutrient input to the coastal ocean, first applications of the new capacity will include measurements in various coastal settings with sandy sediments, different nutrient loadings, different anthropogenic influences and during different seasons using local field sites (e.g. Solent; Itchen and Hamble Estuary, Christchurch Harbour). Measurements will be accompanied by traditional laboratory measurements of environmentally important geochemical and geophysical parameters and laboratory-based flume experiments to investigate the effect of bed structure and sediment transport on sediment fluxes. Depending on the interest, the student could also be involved in the development of new sensors, e.g. for ammonium.
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at and hosted at the National Oceanography Centre Southampton within the Ocean Biogeosciences Group. Specific training will include training on Lab-on-Chip sensors; sediment and pore fluid analyses by ICP-OES, ICP-MS, nutrient analyses and seagoing training. Opportunities for fields trips will be along the South English coast and opportunistic, aligning with NOCs technology and observatory campaigns.
Please see https://inspire-dtp.ac.uk/how-apply for details.
1Chua, E.J., Huettel, M., Fennel, K. and Fulweiler, R.W., 2022. A case for addressing the unresolved role of permeable shelf sediments in ocean denitrification. Limnology and Oceanography Letters, 7(1), pp.11-25. 10.1002/lol2.10218
2Santos, I. R., Eyre, B. D., & Huettel, M. (2012). The driving forces of porewater and groundwater flow in permeable coastal sediments: A review. Estuarine, Coastal and Shelf Science, 98, 1-15. 10.1016/j.ecss.2011.10.024
3Beaton, A. D., Schaap, A. M., Pascal, R., Hanz, R., Martincic, U., Cardwell, C. L., ... & Mowlem, M. C. (2022). Lab-on-chip for in situ analysis of nutrients in the deep sea. ACS sensors, 7(1), 89-98. https://pubs.acs.org/doi/full/10.1021/acssensors.1c01685
