Environmental Engineering Reference
In-Depth Information
rich in nitrogen and also serve to feed
sh and
animals from the reef by supplying wood and
vegetation. Reefs, in turn, protect mangroves and
seagrass from waves and produce sediment in
which the mangroves and seagrass can root. The
input of nutrients through continental run-off
in
inorganic carbon and partial pressure of carbon
dioxide; pCO 2 ) between a reef lagoon and the
surrounding ocean allowed the researchers to
evaluate the system-level performance of the
carbon cycle in the particular reef system. Sur-
face pCO 2 in the lagoons of some atolls and
barrier reefs in the western Paci
uences the productivity of coral reef ecosys-
tem. Suzuki et al. ( 2001 ) estimated the riverine
C:N:P molar ratio in the GBR region as
1,120:30:1, based on their carbon budget calcu-
lation and annual riverine nitrogen and phos-
phorous input estimated by Furnas et al. ( 1995 ).
These ratios are much higher than the Red
fl
c were consis-
tently higher than those of their offshore waters.
The alkalinity decrease in the lagoon water was
attributed to calci
cation of reef organisms. Reef
topography, especially residence time of lagoon
water, affects the carbon budget of coral reefs to
some extent. The offshore
eld
lagoon differences in
pCO 2 from several reefs showed a tendency to
increase with the longer residence time of reef
water. Another important factor controlling car-
bon turnover in coral reefs is proximity to land:
terrestrial carbon and nutrient inputs were clearly
observed in the northern Great Barrier Reef
lagoon as well as a fringing reef of the Ryukyus.
-
ratio for plankton (106:16:1; Red
eld et al.
1963 ), and the ratio of benthic plants in coral
reefs (550:30:1; Atkinson and Smith 1983 ).
Therefore, even if all discharged nutrients are
utilized by biological processes of both plank-
tonic organisms and benthic communities, sur-
plus carbon must remain in the reef water as
oxidized
. Although nutrient inputs may
stimulate organic carbon production in a reef
area, net oxidation of organic matter rather than
net organic carbon
DIC
6.3.3 Calcification
xation would be expected in
the GBR lagoon. A similar in
uence was also
recognized in the Shiraho fringing reef of the
Ryukyu Islands (Kawahata et al. 2000 ). Land-
derived freshwaters, including river water and
groundwater, make a relatively large contribution
to the reef
fl
Corals secrete their skeleton through the cali-
coblastic layer, which is the outer layer of skin or
ectoderm located at the underside of all polyps.
This layer contains specialized cells which con-
tinuously secrete calcium (Ca 2+ ) and bicarbonate
ions (HCO 3 ) to the external environment.
Eventually, this leads to the deposition of a matrix
of calcium carbonate (CaCO 3 or aragonite).
Pumping these ions against a gradient is quite
energy demanding, and this energy is provided by
the coral
s circulation system. These terrestrial
waters exhibit extremely high pCO 2 ,upto
6,400
'
μ
atm, re
fl
ecting enrichments in
AT
and
DIC
due to dissolution of carbonate rocks and
decomposition of organic matter in the soil of
subtropical
uences
may enhance carbon dioxide degassing from the
coastal zone.
The variations of seawater carbon dioxide
system and organic and inorganic carbon pro-
duction of coral reefs were investigated by Su-
zuki and Kawahata ( 2004 ) with respect to
topographic types and oceanographic settings.
Because of dominant carbonate production in
coral reef ecosystems, most coral reefs are likely
to act as a net or at least a potential carbon
dioxide source to the atmosphere. The compari-
son of the seawater carbon dioxide system
parameters
island. These terrestrial
in
fl
s symbiotic zooxanthellae. Many spe-
cies are able to grow over 1 cm (0.4 in.) a month
this way. According to estimations, tropical stony
corals are able to deposit about 10 kg of aragonite
per m 2 per year. The entire process is directly
driven by solar radiation through photosynthesis
by the algae. Because of this,
'
the process is
commonly referred to as
'
light-enhanced calci
-
'
cation
. From several experiments, it has indeed
become clear that this statement is accurate.
Corals deposit signicantly more calcium car-
bonate during the day, and for the stony coral
Stylophora pistillata,
this rate is about four times
in the daytime compared to the night-time.
(pH,
total
alkalinity,
dissolved
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