115
results from the definition of the position of the
system of coordinates, and thus already indicates
the model boundary conditions which will be later
dealt with in more detail. If the zero-point of the
coordinate-system is set by definition to the
boundary between sediment and bottom water, it
follows that the coordinate-system will travel
upwards with the velocity of the sedimentation
rate. Concomitantly, this also implies that sediment particles move downwards relative to the
coordinate-system with the velocity of the
sedimentation rate. This definition may appear
somewhat formalistic, at first, but it becomes more
real and relevant from a quantitative point of view
when diagenetic reactions are studied. Then most
turnovers are limited by the solid phase
components that are introduced into the system
by this form of ‘advection’.
Conceptual Models
Conceptual models and their applications will
be discussed in more detail in Chapter 15 where
computer models will be presented and examples
taken from various fields of application will be
calculated. At this point, conceptual models will
just be mentioned in brief summary and will
contain the most essential statements of this
chapter.
• The description of the diffusive transport by
Fick’s first and second law of diffusion
includes the transport of soluble substances
Fig. 3.27 Advective flow of pore water induced by bottom water flow and documented by O 2 penetration into the
sediment around a small sediment mound (after Ziebis et al. 1996).
3.6
Influence of Bioturbation, Bioirrigation, and Advection
in pore water, which is not mediated by
macroorganisms. In this regard, diffusive
fluxes are always produced by gradients; and
fluxes are always reflected by gradients.
Upon assessment of concentration profiles
with respect to material fluxes, it needs to be
considered whether the depth zones of the
investigated profile are sufficiently (quasi)
stationary with regard to the studied parameter. Non-steady state conditions are appropriately described only by Fick’s second law
of diffusion.
• If no biogeochemical processes can be found
in sediments at all, the pore water should
display constant concentrations from the
top down in a stationary way. Any reactions
taking place in the pore water fraction, or
between pore water and solid phase, will
become visible as a change of the involved
concentration gradients extending across
the depth zone; any changes of the
concentration gradients document the
processes in which pore water has been
involved.
• In principle, bioturbation as a macrobiological
process should not be described in terms of
easily manageable model concepts as can be
done for molecular diffusion. Only if it is
assured that the expansion of a given volume
under study is large enough, and/or provided
that the time-span necessary to make the
results from the definition of the position of the
system of coordinates, and thus already indicates
the model boundary conditions which will be later
dealt with in more detail. If the zero-point of the
coordinate-system is set by definition to the
boundary between sediment and bottom water, it
follows that the coordinate-system will travel
upwards with the velocity of the sedimentation
rate. Concomitantly, this also implies that sediment particles move downwards relative to the
coordinate-system with the velocity of the
sedimentation rate. This definition may appear
somewhat formalistic, at first, but it becomes more
real and relevant from a quantitative point of view
when diagenetic reactions are studied. Then most
turnovers are limited by the solid phase
components that are introduced into the system
by this form of ‘advection’.
Conceptual Models
Conceptual models and their applications will
be discussed in more detail in Chapter 15 where
computer models will be presented and examples
taken from various fields of application will be
calculated. At this point, conceptual models will
just be mentioned in brief summary and will
contain the most essential statements of this
chapter.
• The description of the diffusive transport by
Fick’s first and second law of diffusion
includes the transport of soluble substances
Fig. 3.27 Advective flow of pore water induced by bottom water flow and documented by O 2 penetration into the
sediment around a small sediment mound (after Ziebis et al. 1996).
3.6
Influence of Bioturbation, Bioirrigation, and Advection
in pore water, which is not mediated by
macroorganisms. In this regard, diffusive
fluxes are always produced by gradients; and
fluxes are always reflected by gradients.
Upon assessment of concentration profiles
with respect to material fluxes, it needs to be
considered whether the depth zones of the
investigated profile are sufficiently (quasi)
stationary with regard to the studied parameter. Non-steady state conditions are appropriately described only by Fick’s second law
of diffusion.
• If no biogeochemical processes can be found
in sediments at all, the pore water should
display constant concentrations from the
top down in a stationary way. Any reactions
taking place in the pore water fraction, or
between pore water and solid phase, will
become visible as a change of the involved
concentration gradients extending across
the depth zone; any changes of the
concentration gradients document the
processes in which pore water has been
involved.
• In principle, bioturbation as a macrobiological
process should not be described in terms of
easily manageable model concepts as can be
done for molecular diffusion. Only if it is
assured that the expansion of a given volume
under study is large enough, and/or provided
that the time-span necessary to make the