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.
Cross-references
Aerobic Environments
Microbial Degradation
Nitrogen
Water Quality
NITROGEN
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Synonyms
Azote; Limiting nutrient
Definition
Nitrogen is the seventh element in the Periodic Table of the
Elements. It is an important nutrient for estuarine and
marine life and is essential for the growth of aquatic plants.
Symbol: N, Atomic number: 7, Atomic weight:
14.0067.
Description
Nitrogen is an essential nutrient for synthesizing amino
acids and, consequently, proteins, enzymes, and cell wall
structural components.
Forms: Nitrogen (N) is found as a dissolved salt or in
gaseous form. The elemental form (N 2 ) is the dominant
form present in the atmosphere, comprising approximately
80 % of the total atmospheric gases by volume. In its free
form, N is the primary component of air. Ammonia (NH 3 ),
ammonium (NH 4
+
), nitrite (NO 2
À
), and nitrate (NO 3
À ) are
the principal dissolved inorganic nitrogen (DIN) forms in
coastal systems (Kennish, 1997; Bianchi, 2007).
Sources: Nitrogen enters estuaries through river flow,
atmospheric deposition, and biological fixation.
Demand: The inorganic N forms preferred by aquatic
plants are ammonia and nitrate, and few species
(cyanobacteria and other bacteria) can take advantage
of N 2 or organic N forms. Nitrogen is the primary limiting
factor for estuarine primary production (Day et al., 2012).
Nitrogen limitation leads to a reduction in plant growth
and photosynthetic rates (Falkowski and Raven, 2007).
Isotopes: Only two nitrogen isotopes are stable:
14
N
and
15
N. The most abundant is
14
N (99.634 %). An increase
in
15
N isotope has been observed with increasing trophic
level (Bianchi, 2007).
N Cycle: The biogeochemical cycle is complex and has
two stages. One is external, wherein nitrification,
denitrification, and ammonification processes are
performed through bacterial activities. Nitrification is an
aerobic process and produces the most oxidized nitrogen
compound, nitrate, whereas ammonification transforms
amine radicals into ammonia and free or molecular nitrogen. The other stage is internal, wherein ammonium is
transformed into amine radicals and amino acids during
photosynthesis (Day et al., 2012).
N 2 Fixation: This is the main source of inorganic nitrogen in oligotrophic waters. It is catalyzed by the enzyme
nitrogenase, which is found only in some species of bacteria and photoautotrophic cyanobacteria (Bianchi, 2007).
Only a few phytoplankton carry out N 2 fixation.
Human Impacts: The nitrogen cycle is particularly
affected by human activities in estuaries. Increased
anthropogenic N input to rivers and other influent systems from agricultural, industrial, and urban activities
intensifies the estuarine eutrophication process, stimulating the growth of unwanted aquatic plant species. Nitrate
excess from agricultural activities is transported by rivers, causing the eutrophication of many estuaries worldwide (Kennish, 1997). This process can change the
trophic web and can reduce estuarine biodiversity. Environmental monitoring indicates that the global nitrogen
load to the environment has doubled since the beginning
of the preindustrial era. Nitrogen pollution in aquatic
ecosystems can lead to the development of dead aquatic
zones, such as in the Gulf of Mexico (USA). There is
a consensus that nitrogen pollution of aquatic systems
has reached a global impact.
Bibliography
Bianchi, T. S., 2007. Biogeochemistry of Estuaries. Oxford: Oxford
University Press.
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.
Kennish, M. J., 1997. Practical Handbook of Estuarine and Marine
Pollution. Boca Raton, Florida: CRC Press.
Cross-references
Cyanobacteria
Ecological Stoichiometry
Eutrophication
Macronutrients
Nitrogen
NONPOINT SOURCE POLLUTION
Katherine C. Ridolfi
LimnoTech, Washington, DC, USA
Synonyms
Diffuse pollution
456
NITROGEN
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.
Cross-references
Aerobic Environments
Microbial Degradation
Nitrogen
Water Quality
NITROGEN
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Synonyms
Azote; Limiting nutrient
Definition
Nitrogen is the seventh element in the Periodic Table of the
Elements. It is an important nutrient for estuarine and
marine life and is essential for the growth of aquatic plants.
Symbol: N, Atomic number: 7, Atomic weight:
14.0067.
Description
Nitrogen is an essential nutrient for synthesizing amino
acids and, consequently, proteins, enzymes, and cell wall
structural components.
Forms: Nitrogen (N) is found as a dissolved salt or in
gaseous form. The elemental form (N 2 ) is the dominant
form present in the atmosphere, comprising approximately
80 % of the total atmospheric gases by volume. In its free
form, N is the primary component of air. Ammonia (NH 3 ),
ammonium (NH 4
+
), nitrite (NO 2
À
), and nitrate (NO 3
À ) are
the principal dissolved inorganic nitrogen (DIN) forms in
coastal systems (Kennish, 1997; Bianchi, 2007).
Sources: Nitrogen enters estuaries through river flow,
atmospheric deposition, and biological fixation.
Demand: The inorganic N forms preferred by aquatic
plants are ammonia and nitrate, and few species
(cyanobacteria and other bacteria) can take advantage
of N 2 or organic N forms. Nitrogen is the primary limiting
factor for estuarine primary production (Day et al., 2012).
Nitrogen limitation leads to a reduction in plant growth
and photosynthetic rates (Falkowski and Raven, 2007).
Isotopes: Only two nitrogen isotopes are stable:
14
N
and
15
N. The most abundant is
14
N (99.634 %). An increase
in
15
N isotope has been observed with increasing trophic
level (Bianchi, 2007).
N Cycle: The biogeochemical cycle is complex and has
two stages. One is external, wherein nitrification,
denitrification, and ammonification processes are
performed through bacterial activities. Nitrification is an
aerobic process and produces the most oxidized nitrogen
compound, nitrate, whereas ammonification transforms
amine radicals into ammonia and free or molecular nitrogen. The other stage is internal, wherein ammonium is
transformed into amine radicals and amino acids during
photosynthesis (Day et al., 2012).
N 2 Fixation: This is the main source of inorganic nitrogen in oligotrophic waters. It is catalyzed by the enzyme
nitrogenase, which is found only in some species of bacteria and photoautotrophic cyanobacteria (Bianchi, 2007).
Only a few phytoplankton carry out N 2 fixation.
Human Impacts: The nitrogen cycle is particularly
affected by human activities in estuaries. Increased
anthropogenic N input to rivers and other influent systems from agricultural, industrial, and urban activities
intensifies the estuarine eutrophication process, stimulating the growth of unwanted aquatic plant species. Nitrate
excess from agricultural activities is transported by rivers, causing the eutrophication of many estuaries worldwide (Kennish, 1997). This process can change the
trophic web and can reduce estuarine biodiversity. Environmental monitoring indicates that the global nitrogen
load to the environment has doubled since the beginning
of the preindustrial era. Nitrogen pollution in aquatic
ecosystems can lead to the development of dead aquatic
zones, such as in the Gulf of Mexico (USA). There is
a consensus that nitrogen pollution of aquatic systems
has reached a global impact.
Bibliography
Bianchi, T. S., 2007. Biogeochemistry of Estuaries. Oxford: Oxford
University Press.
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.
Kennish, M. J., 1997. Practical Handbook of Estuarine and Marine
Pollution. Boca Raton, Florida: CRC Press.
Cross-references
Cyanobacteria
Ecological Stoichiometry
Eutrophication
Macronutrients
Nitrogen
NONPOINT SOURCE POLLUTION
Katherine C. Ridolfi
LimnoTech, Washington, DC, USA
Synonyms
Diffuse pollution
456
NITROGEN