230
M. Naeem et al.
nitrogen, phosphorus becomes the limiting element, because
a portion of P is used to counterbalance high nitrate content
(Reynolds 2006). In such circumstances, no algal boom may
arise in heavily eutrophicated water bodies carrying high
content of both N and P. Thus, it is the key point to control
the concentrations of both N and P reasonably for solving
the problem of water-eutrophication. Further, the abundance,
composition and geographical and periodic distribution of
phytoplanktons in a water body vary with the variations in
the chemical composition of natural waters. It is believed
that the growth of phytoplankton is influenced by dissolved
silicate-Si (DSi) concentration in water and its ratio to nitrate (DSi:nitrate-N). When the DSi:nitrate-N atomic ratio is
near 1:1, aquatic food webs associated with diatoms (which
require silicate to flourish) may thrive and the frequency or
size of harmful or noxious algal blooms may increase. In
fact, the DSi:nitrate-N ratio and nitrate-N concentration are
the stout comparative indicators of eutrophication in large
rivers (Turner et al. 2003).
16.4.4 Sources and Functions of Potassium
Potassium (K) is available to plants as potassium ion (K
+
).
Unlike N and P, K does not form any vital organic compounds in the plant. However, the presence of K is vital for
plant growth because K is known to activate many enzymes
necessary for metabolism. Furthermore, K assists in regulating the plant’s water-use by controlling the opening and closing of leaf stomata, where from water is evaporated to cool
the plant. In photosynthesis, K has the role of maintaining
the balance of electrical charges at the site of ATP production
in photosynthesis. K promotes the translocation of photosynthates (sugars) for plant growth or storage in fruits or roots.
Through its role in assisting ATP production, K is involved
in protein synthesis. K has been shown to improve disease
resistance in plants, increase the size of grains and seeds,
and advance the quality of fruits and vegetables (Usherwood
1985; Marschner 2002; Lester et al. 2010).
16.4.5 Role of Potassium in Eutrophication
Potassium constitutes approximately 1 % of the dry weight
of the microbial cell. As the cofactors for some enzymes,
potassium and magnesium stimulate enzyme reactions associated with a synthesis of cell materials (Brdjanovic et al.
1996). The role of potassium in microorganisms responsible
for biological phosphorus removal is even more important.
Potassium functions in cell membrane permeability and
plays major role in phosphate transport between surrounding environment and the cell (Medveczky and Rosemberg
1971). Moreover this cation is an essential counter ion for
gen becomes the limiting element. Nutrient loading to lakes,
estuaries, and coastal oceans has greatly increased through
human activities over the past few decades, increasing the
rate of transformation (eutrophication) of aquatic ecosystem
(Bishop et al. 2006). There are different views on the relationship of nutrient enrichment to water eutrophication and
formation of algal bloom such as (1) When P concentration
in water is low, it may be the limiting factor for inducing
water eutrophication and algal bloom formation; (2) When
P concentration in water increases rapidly, other factors may
become new limiting factors, such as pH, water depth, temperature, light, wave, wind, or other biological factors; (3)
The influence of N and P lasts for a longer time because of
the high development level of our society (Zhao 2004). N
and P input and enrichment in water are the primary factors
to induce water eutrophication. Based on the chemical components of algae, the simulated molecular formula of algae
may be as follows: C 106 H 263 O 110 N 16 P. The formula indicates
that N and P are the elements which account for least proportion in the molecular formula of algae, especially P, which
is the main limiting factor to control the growth of algae in
water (Mainstone and Parr 2002). It was reported that 80 %
of the lake and reservoir eutrophication is restricted by phosphorus, about 10 % of the lake and reservoir eutrophication
is related to nitrogen, and the rest 10 % of the lake and reservoir eutrophication is related to other factors (Zhao 2004).
In many ecosystems, phytoplankton biomass is correlated
with the availability of N or P (Cloern 2001; Bledsoe et al.
2004). The composition of phytoplankton species is also affected by the concentrations of N and P (Reynolds 2006).
The N:P ratio (Redfield ratio) in the water body is an important indicator that points out which nutrient is limiting for
algal growth (eutrophication). If the Redfield ratio is 16:1,
P is most likely the limiting factor for algal growth; while,
lower ratios indicate that N is of great importance (Redfield
et al. 1963; Hodgkiss and Lu 2004). Furthermore, P has been
shown to be the principal limiting nutrient for primary production of phytoplankton in many freshwater bodies (Philips
2002; Sharpley et al. 2003), while N is commonly limiting
in marine ecosystems (Cloern 2001). Nonetheless, there are
many exceptions to this general pattern. In some freshwater
environments, particularly in the tropics and subtropics, N
has been found to be the primary limiting nutrient for phytoplankton production, owing to excessive P load and long
growing seasons. For instances, in the Ten Mile Creek of
Indian River Lagoon, where total P is > 0.2 mg L
−1
, chlorophyll-a and turbidity sharply increased with addition of
available N (0.2∼6.0 mg L
−1
), but is not affected by addition
of reactive P species (Lin et al. 2008). The results indicate
that available N is the limiting nutrient for the growth of
phytoplankton at water bodies with high P. In phosphate-deficient water bodies or those having reasonably good growth
of blue-green algae, which fix enough of the atmospheric
M. Naeem et al.
nitrogen, phosphorus becomes the limiting element, because
a portion of P is used to counterbalance high nitrate content
(Reynolds 2006). In such circumstances, no algal boom may
arise in heavily eutrophicated water bodies carrying high
content of both N and P. Thus, it is the key point to control
the concentrations of both N and P reasonably for solving
the problem of water-eutrophication. Further, the abundance,
composition and geographical and periodic distribution of
phytoplanktons in a water body vary with the variations in
the chemical composition of natural waters. It is believed
that the growth of phytoplankton is influenced by dissolved
silicate-Si (DSi) concentration in water and its ratio to nitrate (DSi:nitrate-N). When the DSi:nitrate-N atomic ratio is
near 1:1, aquatic food webs associated with diatoms (which
require silicate to flourish) may thrive and the frequency or
size of harmful or noxious algal blooms may increase. In
fact, the DSi:nitrate-N ratio and nitrate-N concentration are
the stout comparative indicators of eutrophication in large
rivers (Turner et al. 2003).
16.4.4 Sources and Functions of Potassium
Potassium (K) is available to plants as potassium ion (K
+
).
Unlike N and P, K does not form any vital organic compounds in the plant. However, the presence of K is vital for
plant growth because K is known to activate many enzymes
necessary for metabolism. Furthermore, K assists in regulating the plant’s water-use by controlling the opening and closing of leaf stomata, where from water is evaporated to cool
the plant. In photosynthesis, K has the role of maintaining
the balance of electrical charges at the site of ATP production
in photosynthesis. K promotes the translocation of photosynthates (sugars) for plant growth or storage in fruits or roots.
Through its role in assisting ATP production, K is involved
in protein synthesis. K has been shown to improve disease
resistance in plants, increase the size of grains and seeds,
and advance the quality of fruits and vegetables (Usherwood
1985; Marschner 2002; Lester et al. 2010).
16.4.5 Role of Potassium in Eutrophication
Potassium constitutes approximately 1 % of the dry weight
of the microbial cell. As the cofactors for some enzymes,
potassium and magnesium stimulate enzyme reactions associated with a synthesis of cell materials (Brdjanovic et al.
1996). The role of potassium in microorganisms responsible
for biological phosphorus removal is even more important.
Potassium functions in cell membrane permeability and
plays major role in phosphate transport between surrounding environment and the cell (Medveczky and Rosemberg
1971). Moreover this cation is an essential counter ion for
gen becomes the limiting element. Nutrient loading to lakes,
estuaries, and coastal oceans has greatly increased through
human activities over the past few decades, increasing the
rate of transformation (eutrophication) of aquatic ecosystem
(Bishop et al. 2006). There are different views on the relationship of nutrient enrichment to water eutrophication and
formation of algal bloom such as (1) When P concentration
in water is low, it may be the limiting factor for inducing
water eutrophication and algal bloom formation; (2) When
P concentration in water increases rapidly, other factors may
become new limiting factors, such as pH, water depth, temperature, light, wave, wind, or other biological factors; (3)
The influence of N and P lasts for a longer time because of
the high development level of our society (Zhao 2004). N
and P input and enrichment in water are the primary factors
to induce water eutrophication. Based on the chemical components of algae, the simulated molecular formula of algae
may be as follows: C 106 H 263 O 110 N 16 P. The formula indicates
that N and P are the elements which account for least proportion in the molecular formula of algae, especially P, which
is the main limiting factor to control the growth of algae in
water (Mainstone and Parr 2002). It was reported that 80 %
of the lake and reservoir eutrophication is restricted by phosphorus, about 10 % of the lake and reservoir eutrophication
is related to nitrogen, and the rest 10 % of the lake and reservoir eutrophication is related to other factors (Zhao 2004).
In many ecosystems, phytoplankton biomass is correlated
with the availability of N or P (Cloern 2001; Bledsoe et al.
2004). The composition of phytoplankton species is also affected by the concentrations of N and P (Reynolds 2006).
The N:P ratio (Redfield ratio) in the water body is an important indicator that points out which nutrient is limiting for
algal growth (eutrophication). If the Redfield ratio is 16:1,
P is most likely the limiting factor for algal growth; while,
lower ratios indicate that N is of great importance (Redfield
et al. 1963; Hodgkiss and Lu 2004). Furthermore, P has been
shown to be the principal limiting nutrient for primary production of phytoplankton in many freshwater bodies (Philips
2002; Sharpley et al. 2003), while N is commonly limiting
in marine ecosystems (Cloern 2001). Nonetheless, there are
many exceptions to this general pattern. In some freshwater
environments, particularly in the tropics and subtropics, N
has been found to be the primary limiting nutrient for phytoplankton production, owing to excessive P load and long
growing seasons. For instances, in the Ten Mile Creek of
Indian River Lagoon, where total P is > 0.2 mg L
−1
, chlorophyll-a and turbidity sharply increased with addition of
available N (0.2∼6.0 mg L
−1
), but is not affected by addition
of reactive P species (Lin et al. 2008). The results indicate
that available N is the limiting nutrient for the growth of
phytoplankton at water bodies with high P. In phosphate-deficient water bodies or those having reasonably good growth
of blue-green algae, which fix enough of the atmospheric