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Answers to Problems
process. Process 3 proceeds chemically whereas
process 5 is biologically catalyzed.
Answer 3
Thioploca are chemolithotrophs. If they assimilate CO 2 as the sole carbon source they are chemolithoautotrophs. If they assimilate only acetate
they are chemolithoheterotrophs.
Answer 4
Concentrations of dissolved organic compounds
are very low in the open ocean. Small cells are
relatively more efficient than large cells in taking
up these compounds and can therefore have
higher biomass-specific metabolic rate.
Answer 5
The organic carbon of the plankton cell must first
be buried to a sediment horizon below the penetration depth of sulfate. Here, the particulate
organic material must be degraded by hydrolytic
exoenzymes. The breakdown products are then
fermented by bacteria in several steps to acetate,
hydrogen and CO 2 , which are ultimately converted to methane by methanogenic archaea.
Answer 6
High sensitivity in such a radiotracer experiment
is achieved with a large amount of radioactivity
and a long incubation time (both, of course,
within certain limits). The efficient separation of
the radioactive methane from the sample at the
end of the experiment and the sensitive measurement of its radioactivity are also important. The
sample size is not important as long as all
produced radioactive methane is measured.
Chapter 6
Answer 1
Oxygen is the main electron acceptor during
microbial degradation processes of organic
substance. The energy yield for organisms when
using oxygen is higher than for all other constituents. Products of the other reactions in the
sequence of remineralization (e.g. iron or sulfate
reduction) are reduced species, which are partly
re-oxidized by or under participation of oxygen.
Under this point of view the total benthic
consumption of oxygen is composed by direct
oxygen assimilation and those secondary sinks.
Just because re-oxidation is only one, but in most
cases the dominant pathway for reduced species,
this simplification is not correct. Of course, this
approach of estimation can not be used under
reduced benthic condition, which can prevail for
example in more or less closed basins (e.g. the
Black Sea).
Answer 2
Carbon limited means that not enough reactive
organic carbon is available in order to pursue
mineralization processes. If there is organic
carbon available in excess all potential oxidants
will be used up quickly. These two extremes are
met on the deep sea plains and in shallow marine
environments along the continental margins,
respectively. All types of transitional environments are found in-between.
Answer 3
Denitrification is the only biological process that
produces free nitrogen. It removes fixed nitrogen
compounds and, therefore, exerts a negative
feedback on eutrophication making it a crucial
process for the preservation of life on earth.
Answer 4
Under anoxic conditions iron oxides are reduced
and cannot act as a major carrier of phosphate in
the sediments. Hence, phosphate, which is
released from organic material in the course of
mineralization processes, will mostly diffuse into
the bottom water (and further enhance biological
productivity), thus, decreasing the C org /P org ratio
of the sediments.
Answer 5
The anaerobic oxidation of ammonia can be an
important process in the absence of oxygen, if
nitrite as an alternative electronacceptor is available. Nitrite does usually not accumulate in high
concentrations but may be continuously delivered
by bacteria using nitrate as electron acceptor for
the oxidation of organic carbon. Thus, anammox
Answers to Problems
process. Process 3 proceeds chemically whereas
process 5 is biologically catalyzed.
Answer 3
Thioploca are chemolithotrophs. If they assimilate CO 2 as the sole carbon source they are chemolithoautotrophs. If they assimilate only acetate
they are chemolithoheterotrophs.
Answer 4
Concentrations of dissolved organic compounds
are very low in the open ocean. Small cells are
relatively more efficient than large cells in taking
up these compounds and can therefore have
higher biomass-specific metabolic rate.
Answer 5
The organic carbon of the plankton cell must first
be buried to a sediment horizon below the penetration depth of sulfate. Here, the particulate
organic material must be degraded by hydrolytic
exoenzymes. The breakdown products are then
fermented by bacteria in several steps to acetate,
hydrogen and CO 2 , which are ultimately converted to methane by methanogenic archaea.
Answer 6
High sensitivity in such a radiotracer experiment
is achieved with a large amount of radioactivity
and a long incubation time (both, of course,
within certain limits). The efficient separation of
the radioactive methane from the sample at the
end of the experiment and the sensitive measurement of its radioactivity are also important. The
sample size is not important as long as all
produced radioactive methane is measured.
Chapter 6
Answer 1
Oxygen is the main electron acceptor during
microbial degradation processes of organic
substance. The energy yield for organisms when
using oxygen is higher than for all other constituents. Products of the other reactions in the
sequence of remineralization (e.g. iron or sulfate
reduction) are reduced species, which are partly
re-oxidized by or under participation of oxygen.
Under this point of view the total benthic
consumption of oxygen is composed by direct
oxygen assimilation and those secondary sinks.
Just because re-oxidation is only one, but in most
cases the dominant pathway for reduced species,
this simplification is not correct. Of course, this
approach of estimation can not be used under
reduced benthic condition, which can prevail for
example in more or less closed basins (e.g. the
Black Sea).
Answer 2
Carbon limited means that not enough reactive
organic carbon is available in order to pursue
mineralization processes. If there is organic
carbon available in excess all potential oxidants
will be used up quickly. These two extremes are
met on the deep sea plains and in shallow marine
environments along the continental margins,
respectively. All types of transitional environments are found in-between.
Answer 3
Denitrification is the only biological process that
produces free nitrogen. It removes fixed nitrogen
compounds and, therefore, exerts a negative
feedback on eutrophication making it a crucial
process for the preservation of life on earth.
Answer 4
Under anoxic conditions iron oxides are reduced
and cannot act as a major carrier of phosphate in
the sediments. Hence, phosphate, which is
released from organic material in the course of
mineralization processes, will mostly diffuse into
the bottom water (and further enhance biological
productivity), thus, decreasing the C org /P org ratio
of the sediments.
Answer 5
The anaerobic oxidation of ammonia can be an
important process in the absence of oxygen, if
nitrite as an alternative electronacceptor is available. Nitrite does usually not accumulate in high
concentrations but may be continuously delivered
by bacteria using nitrate as electron acceptor for
the oxidation of organic carbon. Thus, anammox