MEPS 229:127-136 (2002)  -  doi:10.3354/meps229127

Functional approach to sediment reworking by gallery-forming macrobenthic organisms: modeling and application with the polychaete Nereis diversicolor

Frédérique François1,*, Magali Gerino2, Georges Stora3, Jean-Pierre Durbec3, Jean-Christophe Poggiale3

1Observatoire Océanologique de Banyuls, Université Pierre et Marie Curie (Paris VI), CNRS, Laboratoire Arago, BP 44, 66651 Banyuls sur mer cedex, France
2Centre d¹Ecologie des Systèmes Aquatiques Continentaux, 118 route de Narbonne, 31062 Toulouse cedex, France
3Laboratoire d¹Océanographie et de Biogéochimie, Centre d¹Océanologie de Marseille, Campus de Lunimy, Case 901, 163 avenue de Luminy, 13288 Marseille cedex 09, France

ABSTRACT: A mechanistic model has been developed to characterize and quantify sediment-mixing due to macrobenthic organisms that construct gallery systems. The mixing model is time- and space- dependent and employs ordinary differential equations. It uses (1) biological parameters‹the size of the bioturbated zone, rate of biodiffusion and rate of biotransport; (2) physical parametes‹output to the water-column coefficient and rate of physical mixing due to local water currents; and (3) biogeochemical parameters‹decay rate of the tracer. This gallery-diffusor model is based on a combination of 2 processes: biodiffusion in the sediment layer containing very dense gallery systems, and biotransport in the region of tube bottoms. The performance of this gallery-diffusor model is compared with that of the biodiffusor model classically used to describe mixing of such organisms. Both models are applied to conservative tracer profiles measured in laboratory experiments with the polychaete Nereis diversicolor. Our new model provides mechanisms to describe and explain the tracer-profile shapes observed in sediments. It includes rapid particle transport from the upper layer of the sediment to the tube bottom zone, which is not taken into account with the biodiffusor model but which is of great importance in understanding the processes of organic matter degradation in the sedimentary column. It also makes possible the accurate quantification of the different components of the mixing process of an organism (in this study, the polychaete N. diversicolor). The gallery-diffusor model constitutes 1 of 5 elementary components in a global bioturbation model that allows the study, quantification and prediction of sediment reworking by macrobenthic communities according to their functional group and composition and/or to the specific characteristics of the individual organisms.

KEY WORDS: Bioturbation · Nereis diversicolor · Model · Functional groups · Macrobenthos

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