limiting to growth (Day et al., 2012). Nutrient elements
are transferred between organisms and their environment,
and one organism’s wastes can become another organism’s nutrients.
Nutrients Ratio: Nutrient limitation indicates that two
nutrients are out of the appropriate balance. The optimal
nitrogen/phosphorus ratio (N/P-ratio) for phytoplankton
growth is 16:1 (based on molar concentrations) and is
called the Redfield ratio (Redfield et al., 1963). Phosphorus
limitation occurs when there is proportionally less phosphorus than nitrogen (i.e., there is excess nitrogen). Significant deviations from 16 at low N/P-ratios might indicate
potential nitrogen limitation and, at high N/P-ratios, potential phosphorus limitation of phytoplankton primary production. Phosphorus limitation occurs in the spring in
some estuaries when nitrogen availability is high from
storm water runoff. Nitrogen limitation occurs when there
is proportionally less nitrogen than phosphorus (i.e., there
is excess phosphorus). This might affect the biological state
of the ecosystem, in particular the phytoplankton biomass,
species composition, and eventually food web cycles.
Human Interferences: N:P ratios in estuaries have commonly been shown to be lower and/or higher than the
predicted Redfield ratio because of denitrification and
anthropogenic nutrient enrichment processes, respectively
(Day et al., 2012).
Bibliography
Day, J. W., Kemp, M. W., Yánez-Arancibia, A., and Crump, B. C.,
2012. Estuarine Ecology, 2nd edn. Hoboken, New Jersey:
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 seawater. In Hill,
M. N. (ed.), The Sea. New York: John Wiley & Sons, Vol.
2, pp. 26–77.
Cross-references
Bioavailability
Ecological Monitoring
Ecological Stoichiometry
Macronutrients
Micronutrients
NUTRIENTS
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Definition
Nutrients are elements that are functionally involved in the
key processes of life. They are chemical elements or compounds required for autotrophic growth and metabolic
function of estuarine organisms.
Ecological importance
Nutrients are chemical elements of great ecological importance. They include essential elements necessary for primary producers and for metabolic activities of primary
consumers (including C, N, P, Si, S, K, Mg, Na, Fe, Mn,
Zn, Cu, B, Mo, Co, V, and vitamins). Different organisms
have specific elemental requirements. For example,
aquatic plants have the greatest demand for carbon,
nitrogen, and phosphorus. Silicon is an element heavily
utilized by diatoms (Day et al., 2012).
Cycles
The chemical constituents of estuarine organisms are continually cycled among the organisms, water, sediments,
and atmosphere. Nutrient cycling in estuaries is greatly
influenced by the microbial community. Nutrient elements
have cycles that alter their availability in organic and inorganic forms while maintaining continuous production in
estuarine systems (Bianchi, 2007).
Macronutrients
Macronutrients are those nutrients most greatly assimilated
by algae and vascular plants in estuaries. Nitrogen (N),
phosphorus (P), and silicon (Si) are limiting because carbon
(C) is available in large quantities, and the biotic demand
for trace elements is low. Carbon is found in all aquatic ecosystems and is rarely limiting. Organic matter in estuaries
primarily consists of carbon, hydrogen, oxygen, nitrogen,
sulfur, and phosphorus. Phytoplankton and other primary
producers assimilate dissolved inorganic nutrients and
transform them into organic compounds.
Carbon
Carbon is readily available in the marine environment in
carbonate, bicarbonate, and carbon dioxide which are
components of the carbon cycle. Organic carbon is
added to an estuary in both dissolved and particulate
forms (i.e., autochthonous and allochthonous sources).
Allochthonous input can occur from marine and terrestrial
sources, as well as atmospheric transport. Human impact
on the carbon cycle is important. Increased concentrations
of carbon dioxide, methane, and nitrous oxide in the atmosphere are linked with global warming through the greenhouse effect (Stumm and Morgan, 1996). Carbon dioxide
water-to-air fluxes are significant in estuaries (Bianchi,
2007).
Nitrogen
The atmosphere is the largest reservoir of nitrogen which
primarily occurs in diatomic molecular form (N 2 ). Quantitatively, the most important forms are total ammonia nitrogen (NH 3 + NH 4
+ ), nitrate (NO 3
À ), and nitrite (NO 2
À
).
Nitrogen limitation leads to a reduction in autotrophic
growth and photosynthetic rates (Falkowski and Raven,
2007).
464
NUTRIENTS
are transferred between organisms and their environment,
and one organism’s wastes can become another organism’s nutrients.
Nutrients Ratio: Nutrient limitation indicates that two
nutrients are out of the appropriate balance. The optimal
nitrogen/phosphorus ratio (N/P-ratio) for phytoplankton
growth is 16:1 (based on molar concentrations) and is
called the Redfield ratio (Redfield et al., 1963). Phosphorus
limitation occurs when there is proportionally less phosphorus than nitrogen (i.e., there is excess nitrogen). Significant deviations from 16 at low N/P-ratios might indicate
potential nitrogen limitation and, at high N/P-ratios, potential phosphorus limitation of phytoplankton primary production. Phosphorus limitation occurs in the spring in
some estuaries when nitrogen availability is high from
storm water runoff. Nitrogen limitation occurs when there
is proportionally less nitrogen than phosphorus (i.e., there
is excess phosphorus). This might affect the biological state
of the ecosystem, in particular the phytoplankton biomass,
species composition, and eventually food web cycles.
Human Interferences: N:P ratios in estuaries have commonly been shown to be lower and/or higher than the
predicted Redfield ratio because of denitrification and
anthropogenic nutrient enrichment processes, respectively
(Day et al., 2012).
Bibliography
Day, J. W., Kemp, M. W., Yánez-Arancibia, A., and Crump, B. C.,
2012. Estuarine Ecology, 2nd edn. Hoboken, New Jersey:
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 seawater. In Hill,
M. N. (ed.), The Sea. New York: John Wiley & Sons, Vol.
2, pp. 26–77.
Cross-references
Bioavailability
Ecological Monitoring
Ecological Stoichiometry
Macronutrients
Micronutrients
NUTRIENTS
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Definition
Nutrients are elements that are functionally involved in the
key processes of life. They are chemical elements or compounds required for autotrophic growth and metabolic
function of estuarine organisms.
Ecological importance
Nutrients are chemical elements of great ecological importance. They include essential elements necessary for primary producers and for metabolic activities of primary
consumers (including C, N, P, Si, S, K, Mg, Na, Fe, Mn,
Zn, Cu, B, Mo, Co, V, and vitamins). Different organisms
have specific elemental requirements. For example,
aquatic plants have the greatest demand for carbon,
nitrogen, and phosphorus. Silicon is an element heavily
utilized by diatoms (Day et al., 2012).
Cycles
The chemical constituents of estuarine organisms are continually cycled among the organisms, water, sediments,
and atmosphere. Nutrient cycling in estuaries is greatly
influenced by the microbial community. Nutrient elements
have cycles that alter their availability in organic and inorganic forms while maintaining continuous production in
estuarine systems (Bianchi, 2007).
Macronutrients
Macronutrients are those nutrients most greatly assimilated
by algae and vascular plants in estuaries. Nitrogen (N),
phosphorus (P), and silicon (Si) are limiting because carbon
(C) is available in large quantities, and the biotic demand
for trace elements is low. Carbon is found in all aquatic ecosystems and is rarely limiting. Organic matter in estuaries
primarily consists of carbon, hydrogen, oxygen, nitrogen,
sulfur, and phosphorus. Phytoplankton and other primary
producers assimilate dissolved inorganic nutrients and
transform them into organic compounds.
Carbon
Carbon is readily available in the marine environment in
carbonate, bicarbonate, and carbon dioxide which are
components of the carbon cycle. Organic carbon is
added to an estuary in both dissolved and particulate
forms (i.e., autochthonous and allochthonous sources).
Allochthonous input can occur from marine and terrestrial
sources, as well as atmospheric transport. Human impact
on the carbon cycle is important. Increased concentrations
of carbon dioxide, methane, and nitrous oxide in the atmosphere are linked with global warming through the greenhouse effect (Stumm and Morgan, 1996). Carbon dioxide
water-to-air fluxes are significant in estuaries (Bianchi,
2007).
Nitrogen
The atmosphere is the largest reservoir of nitrogen which
primarily occurs in diatomic molecular form (N 2 ). Quantitatively, the most important forms are total ammonia nitrogen (NH 3 + NH 4
+ ), nitrate (NO 3
À ), and nitrite (NO 2
À
).
Nitrogen limitation leads to a reduction in autotrophic
growth and photosynthetic rates (Falkowski and Raven,
2007).
464
NUTRIENTS