231
16 Task of Mineral Nutrients in Eutrophication
polyphosphate in the cell, and is generally an important
factor in the cells energy generation (Buffle 1990; Bianchi
et al. 1995). Enzyme, polyphosphate kinase catalyzes polyphosphate biosynthesis in the presence of magnesium ions
by transferring the terminal phosphoryl group from ATP to
polyphosphate chain. Polyphosphate degradation is driven
by several enzymes which depend on inorganic cations. Magnesium acts as an important counter ion of polyphosphates
too. It is taken up and released simultaneously with phosphate. Therefore, these cations (potassium and magnesium)
are necessary for polyphosphate accumulation and biological phosphorus removal. Potassium ions strongly inhibit the
growth of Microcystis and thus offer a new possibility for
the regulation of Microcystis blooms. Potassium ions, added
as either chlorides or bicarbonates, inhibit the growth of M.
flosaquae C3-9 and M. aeruginosa both found in pond water
and defined media, whereas comparable sodium salts at the
same concentrations do not inhibit Microcystis growth. Parker et al. (1997) studied the samples from five ponds that were
alkaline and eutrophic and contained more than 2.8 mM of
potassium, but none of the ponds had detectable Microcystis
growth. It is, therefore, possible that the potassium concentration in the studied ponds did not influence the prevalence
of Microcystis. They collected the aliquots of KCl-supplemented and unsupplemented pond-water inoculated with
either M. aeruginosa alone or a mixture of M. aeruginosa
and Wolffia arrhiza. In both the cases, the addition of KCl,
but not NaCl, inhibited the growth of M. aeruginosa. In the
second case, W. arrhiza predominated in KCl-supplemented
aliquots but W. arrhiza did not flourish in unsupplemented
or NaCl-supplemented aliquots. These observations indicate
that the addition of KCl is sufficient to alter the prevalence
of M. aeruginosa in pond water. The high-potassium and
low-potassium ponds probably differed in other properties
as well, but the potassium effect was dominant. Zehnder and
Gorham (1960) achieved the greatest yield of M. aeruginosa NRC-1 in modified Fitzgerald medium that contained
one-half or one-fourth of the usual KH 2 PO 4 concentration
and that exhibited Na/K ratios of 9–15. Potassium toxicity
to Microcystis at these concentrations is unexpected, since
K
+
is the major cation inside cells. The cause of potassium
sensitivity of Microcystis is unknown, but several plausible
explanations involve potassium inhibition through sodiumrelated phenomena. For example, most Microcystis-containing ponds are contaminated with detergents and soaps used
for laundry and bathing. Potassium-based instead of sodiumbased detergents and soaps would be less likely to promote
Microcystis blooms. Because the potassium concentrations
that are toxic to Microcystis are not harmful to most other
organisms, potassium compounds may be a safer alternative
to copper sulfate or to other biocides that are currently added
to water supplies to limit Microcystis blooms. The amounts
of potassium that would have to be added might be excessive
for large lakes with rapidly flowing water. The manipulation
of potassium concentrations might affect the amount of Microcystis waters, which are extensively used by humans and
domestic animals. Potassium does not decrease the growth
of the duckweeds in pond water and probably would not affect most types of true algae. Although duckweeds and algae
can be nuisances, they do not produce microcystins (Carmichael 1992; Runnegar et al. 1995) or other toxic products
of Microcystis (Bianchi et al. 1995; Sellner 1997; Guo et al.
1999; Packard et al. 2000). Microcystins are cyclic nonribosomal peptides produced by cyanobacteria such as Microcystis aeruginosa. They can be very toxic for plants and animals
including humans.
16.4.6 Sources and Functions of Calcium
Calcium (Ca) is available to plants as the calcium ion (Ca
2+
).
Ca has a major role in the formation of cell wall and maintaining its plasticity, affecting normal cell division by maintaining cell integrity and membrane permeability (Hirschi
2004). Further, Ca is an activator of several enzyme systems
used in protein synthesis and carbohydrate transfer. Ca combines with anions including those of organic acids, sulfates,
and phosphates. It acts as a detoxifying agent by neutralizing
organic acids in plants. Ca is essential for seed production in
plants such as peanut. Ca indirectly assists in improving crop
yields by reducing soil acidity when soils are limed (Uchida
2000; Marschner 2002).
16.4.7 Role of Calcium in Eutrophication
Biogenic calcium carbonates, calcite, and aragonite, are
major components of the sediments and of the suspended
matter in the water bodies. The adsorption and coprecipitation of phosphate on the suspended matter may play an important role in the cycling and transport of nutrients in water
bodies. The release of phosphate from the suspended matter
may be the source of phosphorus for the onset and sustenance of the algae bloom. Previous studies have shown that
phosphate is strongly adsorbed on the surface of calcite and
aragonite (Gaudette and Berrylyons 1980). This adsorption
has been used to explain why calcium carbonate-rich sediments contain low concentrations of dissolved phosphate in
their pore waters. An understanding of the carbonate system
in the water bodies is important to determine the uptake of
inorganic carbon by phytoplankton and the saturation state
of calcite and aragonite particles that can adsorb phosphate.
The carbonate system can be characterized by measuring the
variables that control the carbonate system (pH, TA, total alkalinity; TCO 2 , total carbonate; and pCO 2 , the partial pressure of CO 2 ; Millero 1995). The carbonate system can be
16 Task of Mineral Nutrients in Eutrophication
polyphosphate in the cell, and is generally an important
factor in the cells energy generation (Buffle 1990; Bianchi
et al. 1995). Enzyme, polyphosphate kinase catalyzes polyphosphate biosynthesis in the presence of magnesium ions
by transferring the terminal phosphoryl group from ATP to
polyphosphate chain. Polyphosphate degradation is driven
by several enzymes which depend on inorganic cations. Magnesium acts as an important counter ion of polyphosphates
too. It is taken up and released simultaneously with phosphate. Therefore, these cations (potassium and magnesium)
are necessary for polyphosphate accumulation and biological phosphorus removal. Potassium ions strongly inhibit the
growth of Microcystis and thus offer a new possibility for
the regulation of Microcystis blooms. Potassium ions, added
as either chlorides or bicarbonates, inhibit the growth of M.
flosaquae C3-9 and M. aeruginosa both found in pond water
and defined media, whereas comparable sodium salts at the
same concentrations do not inhibit Microcystis growth. Parker et al. (1997) studied the samples from five ponds that were
alkaline and eutrophic and contained more than 2.8 mM of
potassium, but none of the ponds had detectable Microcystis
growth. It is, therefore, possible that the potassium concentration in the studied ponds did not influence the prevalence
of Microcystis. They collected the aliquots of KCl-supplemented and unsupplemented pond-water inoculated with
either M. aeruginosa alone or a mixture of M. aeruginosa
and Wolffia arrhiza. In both the cases, the addition of KCl,
but not NaCl, inhibited the growth of M. aeruginosa. In the
second case, W. arrhiza predominated in KCl-supplemented
aliquots but W. arrhiza did not flourish in unsupplemented
or NaCl-supplemented aliquots. These observations indicate
that the addition of KCl is sufficient to alter the prevalence
of M. aeruginosa in pond water. The high-potassium and
low-potassium ponds probably differed in other properties
as well, but the potassium effect was dominant. Zehnder and
Gorham (1960) achieved the greatest yield of M. aeruginosa NRC-1 in modified Fitzgerald medium that contained
one-half or one-fourth of the usual KH 2 PO 4 concentration
and that exhibited Na/K ratios of 9–15. Potassium toxicity
to Microcystis at these concentrations is unexpected, since
K
+
is the major cation inside cells. The cause of potassium
sensitivity of Microcystis is unknown, but several plausible
explanations involve potassium inhibition through sodiumrelated phenomena. For example, most Microcystis-containing ponds are contaminated with detergents and soaps used
for laundry and bathing. Potassium-based instead of sodiumbased detergents and soaps would be less likely to promote
Microcystis blooms. Because the potassium concentrations
that are toxic to Microcystis are not harmful to most other
organisms, potassium compounds may be a safer alternative
to copper sulfate or to other biocides that are currently added
to water supplies to limit Microcystis blooms. The amounts
of potassium that would have to be added might be excessive
for large lakes with rapidly flowing water. The manipulation
of potassium concentrations might affect the amount of Microcystis waters, which are extensively used by humans and
domestic animals. Potassium does not decrease the growth
of the duckweeds in pond water and probably would not affect most types of true algae. Although duckweeds and algae
can be nuisances, they do not produce microcystins (Carmichael 1992; Runnegar et al. 1995) or other toxic products
of Microcystis (Bianchi et al. 1995; Sellner 1997; Guo et al.
1999; Packard et al. 2000). Microcystins are cyclic nonribosomal peptides produced by cyanobacteria such as Microcystis aeruginosa. They can be very toxic for plants and animals
including humans.
16.4.6 Sources and Functions of Calcium
Calcium (Ca) is available to plants as the calcium ion (Ca
2+
).
Ca has a major role in the formation of cell wall and maintaining its plasticity, affecting normal cell division by maintaining cell integrity and membrane permeability (Hirschi
2004). Further, Ca is an activator of several enzyme systems
used in protein synthesis and carbohydrate transfer. Ca combines with anions including those of organic acids, sulfates,
and phosphates. It acts as a detoxifying agent by neutralizing
organic acids in plants. Ca is essential for seed production in
plants such as peanut. Ca indirectly assists in improving crop
yields by reducing soil acidity when soils are limed (Uchida
2000; Marschner 2002).
16.4.7 Role of Calcium in Eutrophication
Biogenic calcium carbonates, calcite, and aragonite, are
major components of the sediments and of the suspended
matter in the water bodies. The adsorption and coprecipitation of phosphate on the suspended matter may play an important role in the cycling and transport of nutrients in water
bodies. The release of phosphate from the suspended matter
may be the source of phosphorus for the onset and sustenance of the algae bloom. Previous studies have shown that
phosphate is strongly adsorbed on the surface of calcite and
aragonite (Gaudette and Berrylyons 1980). This adsorption
has been used to explain why calcium carbonate-rich sediments contain low concentrations of dissolved phosphate in
their pore waters. An understanding of the carbonate system
in the water bodies is important to determine the uptake of
inorganic carbon by phytoplankton and the saturation state
of calcite and aragonite particles that can adsorb phosphate.
The carbonate system can be characterized by measuring the
variables that control the carbonate system (pH, TA, total alkalinity; TCO 2 , total carbonate; and pCO 2 , the partial pressure of CO 2 ; Millero 1995). The carbonate system can be