Algae and Fishes: Benefits and Hazards
471
4 Iron Fertilization
Climatic changes exemplified in ocean acidification and global warming mainly
caused by increased CO 2 concentrations urged the international community to tackle
those critical environmental issues [23]. There are two main proposed scenarios
which include the control of aerosols emissions and to increase oxygen input and
decrease the release of carbon dioxide through inducing massive increases in algal
phytoplankton as a result of ocean iron fertilization (OIF) experiments or biological
pump [24].
Iron fertilization is achieved either naturally by gyres or high dust input or artificially by sinking iron powder/flakes or even iron old vehicles to induce a biomass
increase in algal phytoplankton. This would increase in aquatic animals whose basic
diet is algae [25]. The increase in iron which is an essential micro-nutrient necessary for chlorophyll formation, electron acceptors such as ferredoxin, flavodoxin
and cytochromes and as a cofactor of many enzymes in the algal cell would thereby
increase growth and the uptake of macro-nutrients for phytoplankton growth [26].
According to [23], iron is known to be limiting in the subarctic Pacific, equatorial Pacific, and the Southern Ocean, which are known as high-nutrient and lowchlorophyll (HNLC) regions. Phytoplankton cannot completely utilize the available
macro-nutrients (especially NO 3 ) during photosynthesis due to a lack of iron. For this
reason, primary production in these HNLC regions is relatively low despite the availability of other nutrients. However, the biological pump would only act efficiently
if there is enough supply of macro-nutrients (i.e., nitrate, phosphate, and silicate)
into the euphotic zone [27]. To test this hypothesis, a total of 13 OIF experiments
have been performed. These OIF field experiments demonstrated that primary production could be significantly increased after artificial iron addition [28]. However,
export production efficiency revealed by the OIF experiments was unexpectedly low
compared to production from natural processes in all, except one of the experiments
[23]. The overall conclusion so far is that even though there was an increase in phytoplankton due to iron fertilisation, there was not any pronounced decrease in CO 2
concentrations which continue to rise [29].
4.1 Side Effects of Iron Fertilization
Side effects such as production of green house gases (e.g., N 2 O and CH 4 ) [30]
development of hypoxia/anoxia [31], and toxic algal blooms such as those of the
diatom Pseudo-nitzschia [32] and the dinoflagellate Alexandrinum sp. [33] have
been reported.
[23] reviewed some of those investigations. For methane it is used as a source of
energy for microorganisms and is converted to CO 2 [34, 35]. For N 2 O, it is already
produced in the ocean, so any enhancement of biological production would increase
471
4 Iron Fertilization
Climatic changes exemplified in ocean acidification and global warming mainly
caused by increased CO 2 concentrations urged the international community to tackle
those critical environmental issues [23]. There are two main proposed scenarios
which include the control of aerosols emissions and to increase oxygen input and
decrease the release of carbon dioxide through inducing massive increases in algal
phytoplankton as a result of ocean iron fertilization (OIF) experiments or biological
pump [24].
Iron fertilization is achieved either naturally by gyres or high dust input or artificially by sinking iron powder/flakes or even iron old vehicles to induce a biomass
increase in algal phytoplankton. This would increase in aquatic animals whose basic
diet is algae [25]. The increase in iron which is an essential micro-nutrient necessary for chlorophyll formation, electron acceptors such as ferredoxin, flavodoxin
and cytochromes and as a cofactor of many enzymes in the algal cell would thereby
increase growth and the uptake of macro-nutrients for phytoplankton growth [26].
According to [23], iron is known to be limiting in the subarctic Pacific, equatorial Pacific, and the Southern Ocean, which are known as high-nutrient and lowchlorophyll (HNLC) regions. Phytoplankton cannot completely utilize the available
macro-nutrients (especially NO 3 ) during photosynthesis due to a lack of iron. For this
reason, primary production in these HNLC regions is relatively low despite the availability of other nutrients. However, the biological pump would only act efficiently
if there is enough supply of macro-nutrients (i.e., nitrate, phosphate, and silicate)
into the euphotic zone [27]. To test this hypothesis, a total of 13 OIF experiments
have been performed. These OIF field experiments demonstrated that primary production could be significantly increased after artificial iron addition [28]. However,
export production efficiency revealed by the OIF experiments was unexpectedly low
compared to production from natural processes in all, except one of the experiments
[23]. The overall conclusion so far is that even though there was an increase in phytoplankton due to iron fertilisation, there was not any pronounced decrease in CO 2
concentrations which continue to rise [29].
4.1 Side Effects of Iron Fertilization
Side effects such as production of green house gases (e.g., N 2 O and CH 4 ) [30]
development of hypoxia/anoxia [31], and toxic algal blooms such as those of the
diatom Pseudo-nitzschia [32] and the dinoflagellate Alexandrinum sp. [33] have
been reported.
[23] reviewed some of those investigations. For methane it is used as a source of
energy for microorganisms and is converted to CO 2 [34, 35]. For N 2 O, it is already
produced in the ocean, so any enhancement of biological production would increase