NITRATE REDUCTION
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Synonyms
Denitrification
Definition
Nitrate reduction is the transformation of nitrate to ammonia
through bacterial respiration under anaerobic conditions.
Description
Nitrate (NO 3
À ) is transformed by bacteria in estuaries into
reduced compounds (Day et al., 2012). Bacterial respiration is an oxidation-reduction reaction or redox reaction.
Nitrate reduction takes place in terrestrial, estuarine, and
marine environments and can be limited by nitrate availability. Much nitrate reduction occurs in estuarine bottom
sediments (Kennish, 1997).
Nitrate-reducing bacteria use nitrate as an electron
acceptor to anaerobically oxidize organic matter, which
releases ammonia. This process begins with oxygen
depletion (<0.5 mg/L), and nitrate becomes the primary
oxygen source for the bacteria. Nitrate acts as a substitute
source in the water column and anoxic sediments when
oxygen consumption exceeds production or transportation, and sufficient levels of nitrate are available. Nitratereducing bacteria are facultative anaerobes able to exist
with or without the availability of dissolved oxygen
(Bianchi, 2007).
Large fluxes of (NO 3
À ) from the water column to bottom sediments may be evident in areas where extensive
agricultural fertilization in watersheds has led to increased
rates of nitrate runoff and accumulation in estuarine water
bodies (Kennish, 1997).
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: Wiley-Blackwell.
Kennish, M. J., 1997. Practical Handbook of Estuarine and Marine
Pollution. Boca Raton: CRC Press.
Cross-references
Anaerobic Environments
Anoxia, Hypoxia, and Dead Zones
Anthropogenic Impacts
Nitrification
Nitrogen
NITRIFICATION
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Synonyms
Nitrogen cycle
Definition
Nitrification is a step in the nitrogen (N) cycle in which the
most reduced forms of nitrogen are transformed by bacteria into the most oxidized nitrogen compounds. This is
shown by the aerobic process where NH 3 or NH 4
+ is
oxidized to NO 2
À or NO 3
À through two energy-producing
reactions (Bianchi, 2007).
Description
Nitrification is a microbial process by which reduced
nitrogen compounds (primarily ammonia) are sequentially
oxidized to nitrite and nitrate. It is a critical step in the
nitrogen biogeochemical cycle and can be modified by
human activities (e.g., ammonia is available from
nitrogenous organic matter degradation or input from
agricultural activities; nitrate is widely used in fertilizers).
Nitrification is a two-step process. Transformation of
ammonia and ammonium into nitrite by bacteria of the
genus Nitrosomonas is the first stage. Next, bacteria of
the genus Nitrobacter complete the conversion of nitrite
to nitrate (Day et al., 2012). Nitrate is the end product of
organic N oxidation and is the most stable N compound
in aquatic ecosystems. This process begins when the
amino group (ÀNH 2 ) is transformed into ammonia
(NH 3 ) – ammonification (Bianchi, 2007). The reactions
are generally coupled and proceed rapidly to the nitrate
form. These reactions are rapidly completed, which
explains why nitrite concentrations are typically low,
except in polluted areas.
Nitrogen is considered the limiting nutrient that controls primary production in most estuarine systems. Nitrogen limitation leads to a reduction in growth and
photosynthetic rates (Falkowski and Raven, 2007). The
bacteria responsible for aforementioned transformation
are nitrifying and strictly aerobic, which generates a high
demand for dissolved oxygen to complete the process.
Thus, this process only occurs under aerobic conditions.
It is a very important process for the balance of the trophic
web; therefore, different methods have been used to assess
the intensity of nitrification and abundance of nitrifying
bacteria in estuaries.
Bibliography
Bianchi, T. S., 2007. Biogeochemistry of Estuaries. Oxford: Oxford
University Press.
NITRIFICATION
455
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Synonyms
Denitrification
Definition
Nitrate reduction is the transformation of nitrate to ammonia
through bacterial respiration under anaerobic conditions.
Description
Nitrate (NO 3
À ) is transformed by bacteria in estuaries into
reduced compounds (Day et al., 2012). Bacterial respiration is an oxidation-reduction reaction or redox reaction.
Nitrate reduction takes place in terrestrial, estuarine, and
marine environments and can be limited by nitrate availability. Much nitrate reduction occurs in estuarine bottom
sediments (Kennish, 1997).
Nitrate-reducing bacteria use nitrate as an electron
acceptor to anaerobically oxidize organic matter, which
releases ammonia. This process begins with oxygen
depletion (<0.5 mg/L), and nitrate becomes the primary
oxygen source for the bacteria. Nitrate acts as a substitute
source in the water column and anoxic sediments when
oxygen consumption exceeds production or transportation, and sufficient levels of nitrate are available. Nitratereducing bacteria are facultative anaerobes able to exist
with or without the availability of dissolved oxygen
(Bianchi, 2007).
Large fluxes of (NO 3
À ) from the water column to bottom sediments may be evident in areas where extensive
agricultural fertilization in watersheds has led to increased
rates of nitrate runoff and accumulation in estuarine water
bodies (Kennish, 1997).
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: Wiley-Blackwell.
Kennish, M. J., 1997. Practical Handbook of Estuarine and Marine
Pollution. Boca Raton: CRC Press.
Cross-references
Anaerobic Environments
Anoxia, Hypoxia, and Dead Zones
Anthropogenic Impacts
Nitrification
Nitrogen
NITRIFICATION
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Synonyms
Nitrogen cycle
Definition
Nitrification is a step in the nitrogen (N) cycle in which the
most reduced forms of nitrogen are transformed by bacteria into the most oxidized nitrogen compounds. This is
shown by the aerobic process where NH 3 or NH 4
+ is
oxidized to NO 2
À or NO 3
À through two energy-producing
reactions (Bianchi, 2007).
Description
Nitrification is a microbial process by which reduced
nitrogen compounds (primarily ammonia) are sequentially
oxidized to nitrite and nitrate. It is a critical step in the
nitrogen biogeochemical cycle and can be modified by
human activities (e.g., ammonia is available from
nitrogenous organic matter degradation or input from
agricultural activities; nitrate is widely used in fertilizers).
Nitrification is a two-step process. Transformation of
ammonia and ammonium into nitrite by bacteria of the
genus Nitrosomonas is the first stage. Next, bacteria of
the genus Nitrobacter complete the conversion of nitrite
to nitrate (Day et al., 2012). Nitrate is the end product of
organic N oxidation and is the most stable N compound
in aquatic ecosystems. This process begins when the
amino group (ÀNH 2 ) is transformed into ammonia
(NH 3 ) – ammonification (Bianchi, 2007). The reactions
are generally coupled and proceed rapidly to the nitrate
form. These reactions are rapidly completed, which
explains why nitrite concentrations are typically low,
except in polluted areas.
Nitrogen is considered the limiting nutrient that controls primary production in most estuarine systems. Nitrogen limitation leads to a reduction in growth and
photosynthetic rates (Falkowski and Raven, 2007). The
bacteria responsible for aforementioned transformation
are nitrifying and strictly aerobic, which generates a high
demand for dissolved oxygen to complete the process.
Thus, this process only occurs under aerobic conditions.
It is a very important process for the balance of the trophic
web; therefore, different methods have been used to assess
the intensity of nitrification and abundance of nitrifying
bacteria in estuaries.
Bibliography
Bianchi, T. S., 2007. Biogeochemistry of Estuaries. Oxford: Oxford
University Press.
NITRIFICATION
455