Environmental Engineering Reference
In-Depth Information
CO
2
from higher levels to the deep sea is hampered. Increased saturation levels and
stratification will weaken absorption capabilities of the oceans.
The
is related to fixation of CO
2
by phytoplankton in photosyn-
thesis, which is of the order of 11
“
biological pump
”
16 Gt C per year. This leads to a partial conversion
to CaCO
3
by plankton species sinking down to the lower oceanic levels. This process,
though sequestering some of the original atmospheric CO
2
in solid form, also leads to
partial CO
2
release again.
-
Question
: Why would this be the case?
The biological pump mechanism thus counteracts, decreasing action of the solu-
bility pump. If anthropogenic CO
2
release is to be effectively counteracted, then this
mechanism somehow should be boosted. However, understanding of the mechanism
and its implications is lacking, and one cannot rely on this process to be effectively
controllable in a foreseeable time frame.
The carbon stored in the lithosphere, which is the crust and mantle part of our
Earth, is present in both organic and inorganic forms. Inorganic carbon deposits in
the lithosphere constitute natural carbonate rock materials (e.g., limestone, dolomite),
also present in coal inclusions and oil shales. Organically bound carbon in the litho-
sphere includes litter, humic soil substances, and other organic compounds. CO
2
is
released by different natural geophysical and geochemical processes, such as via vol-
canic eruptions. On the other hand, carbonates in sediments and sedimentary rocks are
also removed from the crust by subduction (due to differences in density of continental
and ocean tectonic plates) to lower lithosphere levels and partially molten beneath
tectonic boundaries.
Terrestrial vegetation, another carbon reservoir, contains about 600
1000 Gt C,
stored mostly as cellulose in the stems and branches of trees. Carbon fluxes related
to terrestrial respiration and decay of CO
2
comprise a value of approximately
61 Gt C
-
year
−1
(Falkowski et al., 2000). Photosynthesis is the chemical process by
which chlorophyll-containing plants and some bacteria can capture CO
2
and organ-
ically convert it with water under the influence of irradiated solar energy. This process
is vital for life on Earth by balancing the amounts of CO
2
and O
2
in the atmosphere
(Raven et al., 2005). This chemical reaction forming a carbohydrate polymer can be
described by the following simple equation:
6
n
CO
2
+5
n
+1
ð
Þ
H
2
O + solar energy
!
C
6
n
H
2
O
ð
Þ
5
n
+1
+6
n
O
2
ð
RX
1
4
Þ
:
:
A number of processes return CO
2
partially back to the atmosphere, namely:
Autotrophic plant respiration, due to consumption by the plant of part of the
carbohydrate polymer to sustain its metabolism
Heterotrophic respiration, whereby soil microbes oxidize plant-derived organic
matter
Fires
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