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Investigating marine benthic ecosystem response to global environmental change

Dr Clare Woulds (SoG), Dr Megan Klaar (SoG)

Project partner(s): Dr Greg Cowie (University of Edinburgh)

Contact email: c.woulds@leeds.ac.uk

Background and Rationale

Marine benthic ecosystems are the locations of a wide range of important processes, including Carbon cycling and nutrient re-cycling. Although shallow marine environments such as estuaries and shelf seas only cover ~5% of the seafloor, they are responsible for 15-20% of marine production1, and large proportions of the turnover of other bioelements. In such environments the benthic fluxes of C, N and P have the potential to exert controls on water quality and productivity in the overlying water column. Estuarine sediments are also one of the most important locations for long term burial of organic C in marine sediments (so called ‘blue carbon’). Therefore biogeochemical processes in shallow marine benthic settings provide important ecosystem services, and influence the quality of an environment which supports many important human activities2.

Increasing atmospheric CO2 concentrations have already led to increases in sea surface temperatures and decreasing seawater pH3, and these trends are forecast to continue into the future. In addition, due to reduced solubility of gases and increased thermal stratification, it is expected that the incidence of hypoxia (low dissolved oxygen concentrations) in marine environments will spread4. Shallow marine benthic environments are particularly vulnerable to these changes.

Temperature, oxygen availability and pH are known to have marked effects on the way that benthic ecosystems function5, 6, 7, however the effect of these factors on the full range of biogeochemical processes is lacking. Furthermore, the effect of altering these important environmental factors is likely to depend on sediment type and season. Finally, most experiments so far have concentrated on manipulating only one key factor, however combinations of factors are likely to have greater impacts on ecosystem functioning than the sum of individual factor manipulations, and this warrants full investigation.

Figure 1. Sediment core incubation equipment (left), and Loch Etive, Scotland (right).

Project Goals and Outline

This studentship will address the question how does marine benthic biogeochemical functioning respond to future temperature, oxygenation and pH conditions, and how does that response depend on initial environmental characteristics?

The study will take an experimental approach, using incubation and manipulation of sediment microcosms, in which the lead supervisor is experienced. Existing core incubation equipment (Fig. 1) will be used to incubate sediment samples under controlled temperature conditions. Importantly the equipment also allows for manipulation and control of dissolved oxygen, and this will be developed to allow for control of CO2. Time series sampling and analysis of overlying water will be undertaken in order to quantify fluxes of oxygen, CO2, nutrients, and trace metals. In addition, stable isotope labelling experiments followed by both bulk and compound-specific stable isotopic analysis may be used to trace C and N through the system in detail, and potentially add detail to the identities of the microorganisms involved.

The student will start the studentship by refining details of the experimental plan, including sampling sites, seasons, and combinations of factors to be manipulated. One potential study location will be Loch Etive (Fig. 1) on the west coast of Scotland, which has the benefit of abundant pre-existing research, and potentially a new research initiative into which the student would be integrated.

Benefits

The successful candidate will benefit from an interdisciplinary outlook gained from working within the River Basins Processes and Management research cluster within the School of Geography. They will also have access to the networks and event provided by water@leeds, and the Leeds NERC DTP.

The successful candidate will become skilled at working at the interface of marine biology/ecology and geochemistry. They will gain experience in conducting marine benthic sampling and experimentation, and in designing and building bespoke equipment. They will also be trained in a wide range of laboratory analytical techniques, ranging from nutrient analysis to preparation of samples for both bulk and compound-specific stable isotopic analysis. Further, they are likely to undergo training in identification of benthic infauna.

An additional part of the training will be through attendance and presenting at national and international conferences. The student will also be encouraged to submit high quality papers for publication throughout the project, and this is supported at the institutional level by the availability of the option to submit the PhD thesis in an alternative ‘thesis by publication’ format.

Informal enquiries should be directed to Clare Woulds (c.woulds@leeds.ac.uk)

References

  1. Berner, R. A.: Burial of organic carbon and pyritic sulphur in the modern ocean: Its geochemical and environmental significance, American Journal of Science, 282, 451-473, 1982.

  2. Costanza, R., dArge, R., deGroot, R., Farber, S., Grasso, M., Hannon, B., Limburg, K., Naeem, S., Oneill, R. V., Paruelo, J., Raskin, R. G., Sutton, P., and vandenBelt, M.: The value of the world's ecosystem services and natural capital, Nature, 387, 253-260, 1997.

  3. Caldeira, K. and Wickett, M. E.: Anthropogenic carbon and ocean pH, Nature, 425, 365-365, 2003.

  4. Helly, J. J. and Levin, L. A.: Global distribution of naturally occurring marine hypoxia on continental margins, Deep Sea Research Part I, 51, 1159-1168, 2004.

  5. Moodley, L., Middelburg, J. J., Soetaert, K., Boschker, H. T. S., Herman, P. M., and Heip, C. H. R.: Similar rapid response to phytodetritus deposition on shallow and deep-sea sediments, Journal of Marine Research, 63, 457-469, 2005.

  6. Woulds, C., Cowie, G. L., Levin, L. A., Andersson, J. H., Middelburg, J. J., Vandewiele, S., Lamont, P. A., Larkin, K. E., Gooday, A. J., Schumacher, S., Whitcraft, C., Jeffreys, R. M., and Schwartz, M. C.: Oxygen as a control on seafloor biological communities and their roles in sedimentary carbon cycling, Limnology and Oceanography, 52, 1698-1709, 2007.

  7. Hall-Spencer, J. M., Rodolfo-Metalpa, R., Martin, S., Ransome, E., Fine, M., Turner, S. M., Rowley, S. J., Tedesco, D., and Buia, M.-C.: Volcanic carbon dioxide vents show ecosystem effects of ocean acidification, Nature, 454, 96-99, 2008.

Related undergraduate subjects:

  • Earth science
  • Environmental science
  • Geography
  • Geology
  • Oceanography