Environmental Engineering Reference
In-Depth Information
strongly support the hypothesis that phy-
toplankton use cadmium to make carbonic anhy-
drase and that this is the reason cadmium is
present in sea water in direct proportion to nutri-
ents such as phosphorous. The authors measured
these effects (the correlations between cadmium
concentration and the concentrations of carbon
dioxide and zinc) as a function of phytoplankton
size. They found that the correlation exists in
every size class, providing strong evidence that
the cadmium-containing carbonic anhydrase
occurs in many species of phytoplankton, not just
in
eld
—
therefore required to determine whether
the
anthropogenic
carbon sources will
enhance
carbon
ux to the deep ocean. A short term
carbon-dioxide disequilibrium experiment was
conducted during the Southern Ocean Iron
Experiment (SOF
ex
) with
14
C isotope and a sig-
ni
fl
cant uptake of HCO
3
−
was observed by
Southern Ocean phytoplankton. Since the
majority of DIC in the ocean is in the form of
bicarbonate, the biological pump may therefore
be insensitive to anthropogenic carbon dioxide.
Approximately half of the DIC uptake observed
was attributable to direct HCO
3
−
uptake, the other
half being direct carbon dioxide uptake mediated
either by passive diffusion or by active uptake
mechanisms. The increase in growth rates and
decrease in carbon dioxide concentration associ-
ated with the iron fertilization did not trigger any
noticeable changes in the mode of DIC acquisi-
tion, indicating that under most environmental
conditions, the carbon dioxide-concentrating
mechanism (CCM) is constitutive. A low-carbon
dioxide treatment induced an increase in uptake
of carbon dioxide, which was attributed to
increased extracellular carbonic anhydrase activ-
ity, at the expense of direct HCO
3
−
transport
across the plasmalemma. Isotopic disequilibrium
experimental results are consistent with Southern
Ocean carbon stable isotope fractionation data
from this and other studies. Although iron fertil-
ization has been shown to signi
T. weissflogii
where it was
rst observed.
5.3
Artificial Enhancement
of Phytoplankton:
Bioremediation
or Biodeterioration?
Bioremediation is the use of living organisms
(primarily micro-organisms) for the removal of
pollutants or any harmful substances from the
biosphere. It relies on biological processes to min-
imize an unwanted environmental impact of the
pollutants. The micro-organisms, in particular,
have the abilities to degrade, detoxify and even
accumulate the harmful organic aswell as inorganic
compounds. Besides them, higher plants have also
been reported to remove such pollutants, primarily
through their ability to accumulate these in their
tissues. The storage and sequestration of carbon by
autotrophs also come under the domain of biore-
mediation, as it is one of the most eco-friendly
approaches to reduce carbon dioxide level of the
atmosphere/ambient media. The phytoplankton
present in the marine and estuarine environments
absorb carbon dioxide for photosynthesis.
Marine phytoplankton have the potential to
signi
cantly enhance
phytoplankton growth and may potentially
increase carbon
ux to the deep ocean, an
important source of the inorganic carbon taken up
by phytoplankton in this study was HCO
3
−
whose
concentration is negligibly affected by the
anthropogenic rise in carbon dioxide.
Bioremediation has emerged during recent
past as most ideal alternative, environment-
friendly and ecologically sound technology for
removing pollutants from the environment,
restoring contaminated sites and preventing fur-
ther pollution. This technology has the potential
to be more socially acceptable when compared to
physical or chemical processes and is, therefore,
expanding the range of organisms to be used for
pollution clean-up. Bioremediation in fact forms
a vital
fl
cantly buffer future increases in atmo-
spheric carbon dioxide levels. However, in order
for carbon dioxide fertilization to have an effect
on carbon sequestration to the deep ocean, the
increase in dissolved carbon dioxide must stim-
ulate primary productivity; that is, marine
phototrophs must be carbon dioxide limited
(Riebesell et al.
1993
). Estimation of the extent of
bicarbonate (HCO
3
−
) uptake in the oceans is
component of
the
so-called green
