726
K. M. G. Mostofa et al.
relatively low (0.19–0.43 μg L −1 ) in the presence of rather elevated amounts of NH 4
+
(0.14–1.36 μM), NO 3
− (22.55–29.50 μM), and PO 4
3− (1.71–2.35 μM), even in the
presence of similar water temperatures (Table 1) (Verlencar et al. 1990). This result
can imply that nutrients have limited influence on photosynthesis in offshore seawater.
A more important effect could be that high contents of algae (or phytoplankton species) in coastal Antarctic seawater ice can absorb irradiance by Chl a bound to PSI
and PSII. A possible consequence would be intracellular or extracellular H 2 O 2 formation, which could directly affect photosynthesis. This effect could be more important in coastal seawater ice than in offshore oceanic seawater ice. The covariation of
dissolved nitrate and phosphate maintained by ocean circulation (Weber and Deutsch
2010) might be a factor that affects photosynthesis in offshore regions. However,
future studies will be required to provide evidence for this mechanism.
4 Factors Controlling Chl a in Natural Waters
There are a numbers of environmental factors that substantially influence Chl a
concentrations or primary production in natural waters. The key factors affecting
photosynthetic and respiratory activities can be detected based on the growth and
development of organisms. They are: (i) seasonal variation in sunlight and UV
radiation, which affect photosynthesis; (ii) occurrence of CO 2 forms; (iii) variation in temperature; (iv) effects of water stress (drought) and precipitation/rainfall;
(v) effects of the amount and nature of DOM and POM; (vi) variation in nutrient
contents; (vii) variation in trace metal ions; (viii) effect of salinity or salt stress;
(ix) effects of toxic pollutants on aquatic microorganisms; (x) effect of size-fractionated phytoplankton; (xi) effects of global warming. These factors are similar
to those affecting primary production or cyanobacterial bloom, which the exception of the effect of global warming (see chapter “Photosynthesis in Nature:
A New Look” and “Impacts of Global Warming on Biogeochemical Cycles in
Natural Waters”).
4.1 Effects of Global Warming
Global warming can affect the heat budget and other physical processes of a water
body, and can subsequently alter the stratification and mixed layer depths (Huisman
et al. 2006; Schindler 1997; Magnuson et al. 1997). Such changes, along with
global warming-induced changes in the seasonal light cycle, can alter the seasonal patterns of Chl contents (or primary production), phytoplankton composition
and nutrient concentrations in SCM and DCM (Huisman et al. 2006; Walsby et al.
1997; O’Reilly et al. 2003; Verburg et al. 2003; Baulch et al. 2005; Fu et al. 2007;
Jöhnk et al. 2008; Castle and Rodgers 2009; Davis et al. 2009; Paerl and Huisman
2009). Correspondingly, an extension of the summer season due to global warming
K. M. G. Mostofa et al.
relatively low (0.19–0.43 μg L −1 ) in the presence of rather elevated amounts of NH 4
+
(0.14–1.36 μM), NO 3
− (22.55–29.50 μM), and PO 4
3− (1.71–2.35 μM), even in the
presence of similar water temperatures (Table 1) (Verlencar et al. 1990). This result
can imply that nutrients have limited influence on photosynthesis in offshore seawater.
A more important effect could be that high contents of algae (or phytoplankton species) in coastal Antarctic seawater ice can absorb irradiance by Chl a bound to PSI
and PSII. A possible consequence would be intracellular or extracellular H 2 O 2 formation, which could directly affect photosynthesis. This effect could be more important in coastal seawater ice than in offshore oceanic seawater ice. The covariation of
dissolved nitrate and phosphate maintained by ocean circulation (Weber and Deutsch
2010) might be a factor that affects photosynthesis in offshore regions. However,
future studies will be required to provide evidence for this mechanism.
4 Factors Controlling Chl a in Natural Waters
There are a numbers of environmental factors that substantially influence Chl a
concentrations or primary production in natural waters. The key factors affecting
photosynthetic and respiratory activities can be detected based on the growth and
development of organisms. They are: (i) seasonal variation in sunlight and UV
radiation, which affect photosynthesis; (ii) occurrence of CO 2 forms; (iii) variation in temperature; (iv) effects of water stress (drought) and precipitation/rainfall;
(v) effects of the amount and nature of DOM and POM; (vi) variation in nutrient
contents; (vii) variation in trace metal ions; (viii) effect of salinity or salt stress;
(ix) effects of toxic pollutants on aquatic microorganisms; (x) effect of size-fractionated phytoplankton; (xi) effects of global warming. These factors are similar
to those affecting primary production or cyanobacterial bloom, which the exception of the effect of global warming (see chapter “Photosynthesis in Nature:
A New Look” and “Impacts of Global Warming on Biogeochemical Cycles in
Natural Waters”).
4.1 Effects of Global Warming
Global warming can affect the heat budget and other physical processes of a water
body, and can subsequently alter the stratification and mixed layer depths (Huisman
et al. 2006; Schindler 1997; Magnuson et al. 1997). Such changes, along with
global warming-induced changes in the seasonal light cycle, can alter the seasonal patterns of Chl contents (or primary production), phytoplankton composition
and nutrient concentrations in SCM and DCM (Huisman et al. 2006; Walsby et al.
1997; O’Reilly et al. 2003; Verburg et al. 2003; Baulch et al. 2005; Fu et al. 2007;
Jöhnk et al. 2008; Castle and Rodgers 2009; Davis et al. 2009; Paerl and Huisman
2009). Correspondingly, an extension of the summer season due to global warming