Sediment Reworking and Bioturbation Assessment Methods

Presented by: Michelle Johnston

Outline

IntroductionBioturbation

MethodsDirect MethodsParticle-Tracer Methods

DiscussionComparison

Conclusions

Introduction: Bioturbation

Bioturbation: the displacement and mixing of sediment particles

Importance: indicator of benthic community changes

Direct Methods

First direct approach to assess bioturbation (Davison, 1891)

Main issue: difficult because reworked sediments may be unconsolidated and spread laterally

Collections of Castings Entrapment

Direct Methods

comparing height differences in the sediment-water interface between consecutive images through the use of protrusive lasers that skim the sediment surface

Surface Image Analysis

Leveling & Microtopography Mapping

(Maire et al., 2008)

Summary: Direct Methods

Particle-Tracer Methods

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

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

Discussion

Rough qualitative estimate of the rate of sediment reworking

Direct Methods Example Particle-Tracer Example

Accurately asses vertical component of bioturbation

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

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 Wadden Sea. 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 Brissopsis lyrifera 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.

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 Stylodrilus heringianus (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.

Direct Comparison Study

Maire et 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

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

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