Krumbein, W. C., 1938. Size frequency distributions of sediments
and the normal phi curve. Journal of Sedimentary Petrology, 8,
84–90.
Tanner, W. F., 1969. The particle size scale. Journal of Sedimentary
Petrology, 39, 809–812.
Cross-references
Estuarine Sediment Composition
Sediment Grain Size
Sediment Sorting
PHOSPHORUS
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Definition
Phosphorus (P) is an essential chemical element for
aquatic life. It has an atomic number of 15, and its atomic
mass is 31 u.
Sources
Phosphorus enters rivers, streams, and other watershed
influent systems through the weathering of phosphoric
rock, and it is then transported to estuaries. Industrial, agricultural, and domestic effluents are additional sources of
this element (Bianchi, 2007). Detergents commonly
include phosphates as a component; domestic sewage
therefore generally carries high levels of phosphorus to
coastal aquatic systems. Phosphorus can reach elevated
concentrations in estuaries, where it can compromise
water quality. In estuarine ecosystems, phosphorus is
rarely encountered in molecular form but occurs as phosphate consisting of a phosphorus atom bonded to four
oxygen atoms (PO 4
3À
). The phosphorus cycle in estuaries
is regulated in large part by the activities of microbes
(Day et al., 2012).
Essential Nutrient
Phosphorus is essential for the growth of autotrophs,
which transform orthophosphate into mononucleotide
acids (ATP, ADP), phospholipids, fatty acids, and
proteins (structural or genetic information for proteins
such as DNA and RNA) during photosynthesis
(Day et al., 2012). It enters the trophic web through
primary consumers. Organic matter regeneration, ion
exchange, and re-suspension processes maintain high
levels of bioavailable dissolved phosphate (Bianchi,
2007). The optimal nitrogen:phosphorus ratio (N:P ratio)
for phytoplankton growth is 16:1 and is called the
Redfield ratio (Redfield et al., 1963). N:P ratios in
estuaries are commonly lower and/or higher than the
predicted Redfield ratio (Bianchi, 2007).
Eutrophication
In estuaries, an excess of phosphorus can be problematic,
often resulting in eutrophication under appropriate light
and temperature conditions, which can impact the structure and function of these ecosystems. For this reason,
phosphorus is employed as a chemical indicator of the
health of estuaries, and it is usually monitored in water
quality surveys.
Forms
Phosphorus is often available as dissolved inorganic
phosphorus (DIP), dissolved organic phosphorus
(DOP), and particulate organic phosphorus (POP). DIP
is rapidly assimilated by algae during the photosynthetic
process. In aquatic ecosystems, the orthophosphate
ion (PO 4
3À ) is the most oxidized and stable compound.
The phosphorus cycle is relatively simple compared with
that of the nitrogen cycle (Day et al., 2012), because
phosphorus has no gas phase and is less subjected to biological transformation. In estuarine environments, DIP is
highly reactive and forms complex compounds with
metals, including iron and manganese (oxides and
hydroxides), which form insoluble precipitates under
aerobic conditions. However, it may return to the
dissolved form when the redox conditions are sufficiently reducing. Due to the high charge on this ion, it
may be fixed on particle surfaces, including clays
and organic detritus that act as cations. Such sorptionrelease processes comprise a buffering mechanism for
DIP in estuaries, maintaining DIP bioavailability
such that it is not considered a limiting nutrient
(Bianchi, 2007).
Bibliography
Bianchi, T. S., 2007. Biogeochemistry of Estuaries. Oxford: Oxford
University Press.
Day, J. W., Crump, B. C., Kemp, M. W., and Yánez-Arancibia, A.,
2012. Estuarine Ecology, 2nd edn. Hoboken: Wiley-Blackwell.
Falkowski, P. G., and Raven, J. A., 2007. Aquatic Photosynthesis,
2nd edn. Princeton: Princeton University Press.
Redfield, A. C., Ketchum, B. H., and Richards, F. A., 1963.
The influence of organisms on the composition of sea-water. In
Hill, M. N. (ed.), The Sea. New York: John Wiley and Sons,
Vol. 2.
Cross-references
Algal Blooms
Anthropogenic Impacts
Ecological Stoichiometry
Eutrophication
Macronutrients
Nonpoint Source Pollution
Nutrient Dynamics
484
PHOSPHORUS
and the normal phi curve. Journal of Sedimentary Petrology, 8,
84–90.
Tanner, W. F., 1969. The particle size scale. Journal of Sedimentary
Petrology, 39, 809–812.
Cross-references
Estuarine Sediment Composition
Sediment Grain Size
Sediment Sorting
PHOSPHORUS
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Definition
Phosphorus (P) is an essential chemical element for
aquatic life. It has an atomic number of 15, and its atomic
mass is 31 u.
Sources
Phosphorus enters rivers, streams, and other watershed
influent systems through the weathering of phosphoric
rock, and it is then transported to estuaries. Industrial, agricultural, and domestic effluents are additional sources of
this element (Bianchi, 2007). Detergents commonly
include phosphates as a component; domestic sewage
therefore generally carries high levels of phosphorus to
coastal aquatic systems. Phosphorus can reach elevated
concentrations in estuaries, where it can compromise
water quality. In estuarine ecosystems, phosphorus is
rarely encountered in molecular form but occurs as phosphate consisting of a phosphorus atom bonded to four
oxygen atoms (PO 4
3À
). The phosphorus cycle in estuaries
is regulated in large part by the activities of microbes
(Day et al., 2012).
Essential Nutrient
Phosphorus is essential for the growth of autotrophs,
which transform orthophosphate into mononucleotide
acids (ATP, ADP), phospholipids, fatty acids, and
proteins (structural or genetic information for proteins
such as DNA and RNA) during photosynthesis
(Day et al., 2012). It enters the trophic web through
primary consumers. Organic matter regeneration, ion
exchange, and re-suspension processes maintain high
levels of bioavailable dissolved phosphate (Bianchi,
2007). The optimal nitrogen:phosphorus ratio (N:P ratio)
for phytoplankton growth is 16:1 and is called the
Redfield ratio (Redfield et al., 1963). N:P ratios in
estuaries are commonly lower and/or higher than the
predicted Redfield ratio (Bianchi, 2007).
Eutrophication
In estuaries, an excess of phosphorus can be problematic,
often resulting in eutrophication under appropriate light
and temperature conditions, which can impact the structure and function of these ecosystems. For this reason,
phosphorus is employed as a chemical indicator of the
health of estuaries, and it is usually monitored in water
quality surveys.
Forms
Phosphorus is often available as dissolved inorganic
phosphorus (DIP), dissolved organic phosphorus
(DOP), and particulate organic phosphorus (POP). DIP
is rapidly assimilated by algae during the photosynthetic
process. In aquatic ecosystems, the orthophosphate
ion (PO 4
3À ) is the most oxidized and stable compound.
The phosphorus cycle is relatively simple compared with
that of the nitrogen cycle (Day et al., 2012), because
phosphorus has no gas phase and is less subjected to biological transformation. In estuarine environments, DIP is
highly reactive and forms complex compounds with
metals, including iron and manganese (oxides and
hydroxides), which form insoluble precipitates under
aerobic conditions. However, it may return to the
dissolved form when the redox conditions are sufficiently reducing. Due to the high charge on this ion, it
may be fixed on particle surfaces, including clays
and organic detritus that act as cations. Such sorptionrelease processes comprise a buffering mechanism for
DIP in estuaries, maintaining DIP bioavailability
such that it is not considered a limiting nutrient
(Bianchi, 2007).
Bibliography
Bianchi, T. S., 2007. Biogeochemistry of Estuaries. Oxford: Oxford
University Press.
Day, J. W., Crump, B. C., Kemp, M. W., and Yánez-Arancibia, A.,
2012. Estuarine Ecology, 2nd edn. Hoboken: Wiley-Blackwell.
Falkowski, P. G., and Raven, J. A., 2007. Aquatic Photosynthesis,
2nd edn. Princeton: Princeton University Press.
Redfield, A. C., Ketchum, B. H., and Richards, F. A., 1963.
The influence of organisms on the composition of sea-water. In
Hill, M. N. (ed.), The Sea. New York: John Wiley and Sons,
Vol. 2.
Cross-references
Algal Blooms
Anthropogenic Impacts
Ecological Stoichiometry
Eutrophication
Macronutrients
Nonpoint Source Pollution
Nutrient Dynamics
484
PHOSPHORUS