Sediment Reworking and Bioturbation Assessment Methods

1. Presented by: Michelle Johnston Sediment Reworking and Bioturbation Assessment Methods

2. Outline • Introduction Bioturbation • Methods Direct Methods Particle-Tracer Methods • Discussion Comparison • Conclusions

3. Introduction: Bioturbation • Bioturbation: the displacement and mixing of sediment particles • Importance: indicator of benthic community changes

4. Direct Methods Collections of Castings Entrapment • First direct approach to assess bioturbation (Davison, 1891) • Main issue: difficult because reworked sediments may be unconsolidated and spread laterally

5. Direct Methods Leveling & Microtopography Mapping Surface Image Analysis comparing height differences in the sediment-water interface between consecutive images through the use of protrusive lasers that skim the sediment surface (Maireet al., 2008)

6. Summary: Direct Methods

7. Particle-Tracer Methods

8. Radionuclides • Naturally occurring tracers in the water column: 234Th, 228Th, 32Si, 14C, 210Pb and 7Be • Radionuclides are quantified through the use of alpha or gamma spectroscopy, and isotopic profiles are constructed

9. Deliberately Introduced Particle Tracers • Microtaggants are passive, rigid plastic particles that are coated in blue paint • Luminophores are UV fluorescently coated sediment particles • These visually distinguishable tracers are counted under a dissecting microscope

10. Discussion Direct Methods Example Particle-Tracer Example • Rough qualitative estimate of the rate of sediment reworking • Accurately asses vertical component of bioturbation

11. Conclusion • Not one method can be used as a set standard; all methods have their own drawbacks and disadvantages • Microtopography mapping is one of the more progressive direct approaches – technological advances to improve laser telemetry • Naturally occurring radionuclide analysis is a dependable and proven technique in assessing bioturbation

12. Selected References • Arnold, J.R., Al-Salih, H.A., 1955. Beryllium-7 Produced by cosmic Rays. Science, New Series. 121(3144): 451-453. • Blair, N.E., Levin, L.A., DeMaster, D., Plaia, G., 1996. The short term fate of fresh algal carbon in continental slope sediments. Limnology and Oceanography 41:1208- 1219. • Cadée, G.C., 1976. Sediment reworking by Arenicola marina on tidal flats in the Dutch WaddenSea. Netherlands Journal of Sea Research 10:440–460. • Davis, R.B., 1974. Stratigraphic effects of tubificids in profundal lake sediments. Limnology and Oceanography 19:466–488. • Davison, C., 1891. On the amount of sand brought up by lobworms to the surface. Geological Magazine 8:489–493. • Glass, B.P., Baker, R.N., Storzer, D., Wagner, G.A., 1973. North American microtektites from the Caribbean Sea and their fission track age. Earth and Planetary Science Letters 19:184–192. • Hollertz, K., Duchêne, J.C., 2001. Burrowing behaviour and sediment reworking in the heart urchin Brissopsislyrifera Forbes (Spatangoida). Marine Biology 139:951–957. • Lohrer, A.M., Thrush, S.F., Hunt, L., Hancock, N., Lundquist, C., 2005. Rapid reworking of subtidal sediments by burrowing spatangoid urchins. Journal of Experimental Marine Biology and Ecology 321:155–169.

13. Selected References • Pearson, T.H., Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanographic Marine Biology Annual Review. 16: 229-311. • Sandnes, J., Forbes, T., Hansen, R., Sandnes, B., 2000. Influence of particle type and faunal activity on mixing of di(2-ethylhexyl) phthalate (DEHP) in natural sediments. Marine Ecology Progress Series 197:151–167. • Santschi, P. H., Allison, M., Asbill, S., Perlet, A. B., Cappellino, S., Dobbs, C., McShea, L., 1999. Sediment transport and Hg recovery in Lavaca Bay, as evaluated from radionuclide and Hg distributions. Environmental Science and Technology 33: 378-391. • Suchanek, T.H., Colin, P.L., McMurty, G.M., Suchanek, C.S., 1986. Bioturbation and redistribution of sediment radionuclides in Enewetak Atoll lagoon by callianassid shrimp: biological aspects. Bulletin of Marine Science 38:144–154. • White, D.S., Klahr, P.C., Robbins, J.A., 1987. Effects of temperature and density on sediment reworking by Stylodrilusheringianus(Oligochaeta: Lumbriculidae). Journal of Great Lakes Research 13: 147–1. • Yeager, K.M., Santschi, P.H., Rowe, G.T., 2004. Sediment accumulation and radionuclide inventories (239,240Pu, 210Pb and 234Th) in the northern Gulf of Mexico, as influenced by organic matter and macrofaunal density. Marine Chemistry. 91: 1-14.

14. Direct Comparison Study • Maireet al., 2007 • Used surface image analysis and particle tracer method (luminosphores) • A more distinct relationship between direct observation of siphon activity as opposed to the particle tracer method • The choice between direct and particle tracer approaches relies on the ecological/biogeochemical questions

15. In our lab… • 234Th ( days), is used in determining the mixing rates in sediments • fallout radionuclide 210Pb - a part of the 238U decay series = relative dating between 20-120 years • 137Cs ( years), which can be used alongside 210Pb to validate estimated sedimentation rates

16. Modelling • Two main types of continuum models • Local models • Biodiffusion model – local mixing • Non-local sediment reworking models • Used when particular features in tracer profiles appear that cannot be explained by the biodiffusion analogy