6 Sediment Dynamics by Bioturbating Organisms
G.C.CADEE
6.1 Introduction
Judging from the few pages dealing with bioturbation in books on coastal
sediment dynamics (e. g. Hails and Carr 1975; Dyer 1986), one might conclude
bioturbation to be unimportant in sediment dynamics: waves and (tidal) currents have a predominant role in sediment transport and erosion. Is this conclusion wrong? Probably not: For the Lister Basin near Sylt, Bayer! et al. (1998)
conclude that reworking of sediments is mainly physical, certainly in exposed
parts hardly influenced by bioturbation. With an increase in current strength
and/or wave exposure (energy in the environment), sediment transport will
increase. This is not the case with bioturbation. In very high-energy environments, sediment transport is too high for benthic organisms to live, so bioturbation is also absent. Under absence of water movement, benthic organisms also will not thrive. If oxygen deficiency also occurs they may be even
completely absent. In between these extremes of environmental energy,
benthic organisms and, therefore, bioturbation play a role. Sediment transport by bioturbation is mainly vertical, within the sediment column, whereas
currents and waves transport sediment along the bottom. However, both are
linked, e. g. sediment brought to the surface by organisms may be taken up
and dispersed by currents. We can visualise sediment transport in a very
simple model (Fig. 6.1) in which energy is on the X-axis, sediment dynamics
on the Y-axis. Sediment dynamics (sediment movement) due to physical
forces increases continuously with increasing energy. Sediment dynamics by
bioturbating organisms is absent at very low- and very high-energy levels and
is important in between at medium-energy levels. It is at these mediumenergy levels that bioturbation adds to sediment dynamics in coastal areas. In
high-energy environments - those most interesting for students of coastal
sediment dynamics - the contribution of bioturbation to sediment dynamics
is relatively less important.
Ecological Studies, Vol. 151
K. Reise (ed.) Ecological Comparisons
of Sedimentary Shores
© Springer-Verlag Berlin Heidelberg 2001
G.C.CADEE
6.1 Introduction
Judging from the few pages dealing with bioturbation in books on coastal
sediment dynamics (e. g. Hails and Carr 1975; Dyer 1986), one might conclude
bioturbation to be unimportant in sediment dynamics: waves and (tidal) currents have a predominant role in sediment transport and erosion. Is this conclusion wrong? Probably not: For the Lister Basin near Sylt, Bayer! et al. (1998)
conclude that reworking of sediments is mainly physical, certainly in exposed
parts hardly influenced by bioturbation. With an increase in current strength
and/or wave exposure (energy in the environment), sediment transport will
increase. This is not the case with bioturbation. In very high-energy environments, sediment transport is too high for benthic organisms to live, so bioturbation is also absent. Under absence of water movement, benthic organisms also will not thrive. If oxygen deficiency also occurs they may be even
completely absent. In between these extremes of environmental energy,
benthic organisms and, therefore, bioturbation play a role. Sediment transport by bioturbation is mainly vertical, within the sediment column, whereas
currents and waves transport sediment along the bottom. However, both are
linked, e. g. sediment brought to the surface by organisms may be taken up
and dispersed by currents. We can visualise sediment transport in a very
simple model (Fig. 6.1) in which energy is on the X-axis, sediment dynamics
on the Y-axis. Sediment dynamics (sediment movement) due to physical
forces increases continuously with increasing energy. Sediment dynamics by
bioturbating organisms is absent at very low- and very high-energy levels and
is important in between at medium-energy levels. It is at these mediumenergy levels that bioturbation adds to sediment dynamics in coastal areas. In
high-energy environments - those most interesting for students of coastal
sediment dynamics - the contribution of bioturbation to sediment dynamics
is relatively less important.
Ecological Studies, Vol. 151
K. Reise (ed.) Ecological Comparisons
of Sedimentary Shores
© Springer-Verlag Berlin Heidelberg 2001