105
gaseous phase and its concentration present in
aqueous solution (at least one hour), the gas
phase is ready to be sampled by puncturing the
rubber cap that seals the vial with a syringe.
3.5
In-situ Measurements
The desire to measure the properties of a natural
system, or profiles of properties, in situ, appears
to be obvious whenever the system becomes subject to a change as a result of the sample collection procedure. In principle, this is applicable to
many aquatic geosystems. Especially where solid
and aquatic phases come together in a limited
space, this boundary constitutes the site of
essential reactions. Such a site is the surface
boundary between bottom water and sediment. An
essential biogeochemical process of early diagenesis is exemplified by the permeation of
oxygen into the young sediment by diffusion, but
also by the activity of organisms. The oxygen in
the sediment reacts in many ways (cf. Chaps. 5
and 6). In part, the oxygen is depleted in the
course of oxidizing organic matter, in part, upon
re-oxidizing various reduced inorganic species
(e.g. Fe
2+
, Mn
2+
).
In organic-rich and highly reactive sediments,
the depletion of oxygen previously imported by
means of diffusion already occurs in the
uppermost millimeters of the sediment (cf. Sect.
3.5). However, these organic-rich and young
sediments are mostly extremely rich in water
(porosity values up to 0.9) and very soft, so that
every sample removal will most likely induce a
perturbation of the boundary zone which is, in a
crucial way, maintained by diffusion.
Moreover, the actively mediated import of
oxygen into the young sediment, which runs
parallel to diffusion, and which is transported by
the organisms living therein, will function
‘naturally’ only as long as these organism are not
‘unnaturally’ treated. Any interference caused by
sampling is certain to be regularly coupled to a
change of temperature, pressure and the quality of
the bottom water, and thus means a change in the
‘normal’ living conditions. Here as well, it is of
special interest to measure the active import of
oxygen into the sediment governed by biological
activity in situ. (cf. Sect. 3.6). An overview of the
literature references and the state of knowledge
related to the in situ measurement methods and
Fig. 3.19 Schematic representation of a Lander System
which is also used in the deep sea. The machinery sinks
freely, without any attachment, to the ocean floor where it
carries out measurements and returns back to the surface after
the release of ballast. The depicted version stands about 2-3
m in height. It is designed to conduct incubation experiments
at the ocean floor, yet similar landers are used to record/
monitor in situ microprofiles of the oxygen concentration
through the sediment/bottom water boundary layer. The perspective shows only two of the three feet upon which the
lander stands (after Jahnke and Christiansen 1989).
1
2
4
5
5
6
3
8
7
9
1
2
3
4
5
6
7
9
8
Glass floats (1 of 8)
Main ballast release
Secondary ballast release (1 of 3)
Electronic pressure case
Sampling racks
Syringes
Expendable ballast
Chamber lid and stirring mechanism
Chamber & chamber scoop
7
techniques applied to capture the biogeochemical
processes in the water/sediment transition zone
has been provided by Viollier et al. (2003).
3.5
In situ Measurements
gaseous phase and its concentration present in
aqueous solution (at least one hour), the gas
phase is ready to be sampled by puncturing the
rubber cap that seals the vial with a syringe.
3.5
In-situ Measurements
The desire to measure the properties of a natural
system, or profiles of properties, in situ, appears
to be obvious whenever the system becomes subject to a change as a result of the sample collection procedure. In principle, this is applicable to
many aquatic geosystems. Especially where solid
and aquatic phases come together in a limited
space, this boundary constitutes the site of
essential reactions. Such a site is the surface
boundary between bottom water and sediment. An
essential biogeochemical process of early diagenesis is exemplified by the permeation of
oxygen into the young sediment by diffusion, but
also by the activity of organisms. The oxygen in
the sediment reacts in many ways (cf. Chaps. 5
and 6). In part, the oxygen is depleted in the
course of oxidizing organic matter, in part, upon
re-oxidizing various reduced inorganic species
(e.g. Fe
2+
, Mn
2+
).
In organic-rich and highly reactive sediments,
the depletion of oxygen previously imported by
means of diffusion already occurs in the
uppermost millimeters of the sediment (cf. Sect.
3.5). However, these organic-rich and young
sediments are mostly extremely rich in water
(porosity values up to 0.9) and very soft, so that
every sample removal will most likely induce a
perturbation of the boundary zone which is, in a
crucial way, maintained by diffusion.
Moreover, the actively mediated import of
oxygen into the young sediment, which runs
parallel to diffusion, and which is transported by
the organisms living therein, will function
‘naturally’ only as long as these organism are not
‘unnaturally’ treated. Any interference caused by
sampling is certain to be regularly coupled to a
change of temperature, pressure and the quality of
the bottom water, and thus means a change in the
‘normal’ living conditions. Here as well, it is of
special interest to measure the active import of
oxygen into the sediment governed by biological
activity in situ. (cf. Sect. 3.6). An overview of the
literature references and the state of knowledge
related to the in situ measurement methods and
Fig. 3.19 Schematic representation of a Lander System
which is also used in the deep sea. The machinery sinks
freely, without any attachment, to the ocean floor where it
carries out measurements and returns back to the surface after
the release of ballast. The depicted version stands about 2-3
m in height. It is designed to conduct incubation experiments
at the ocean floor, yet similar landers are used to record/
monitor in situ microprofiles of the oxygen concentration
through the sediment/bottom water boundary layer. The perspective shows only two of the three feet upon which the
lander stands (after Jahnke and Christiansen 1989).
1
2
4
5
5
6
3
8
7
9
1
2
3
4
5
6
7
9
8
Glass floats (1 of 8)
Main ballast release
Secondary ballast release (1 of 3)
Electronic pressure case
Sampling racks
Syringes
Expendable ballast
Chamber lid and stirring mechanism
Chamber & chamber scoop
7
techniques applied to capture the biogeochemical
processes in the water/sediment transition zone
has been provided by Viollier et al. (2003).
3.5
In situ Measurements