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The Nitrogen cycle
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Nitrogen cycle
Unlike phosphorus (PO43- = +V), nitrogen displays many different
oxidation states (+V to –III) in seawater. Nitrogen exists in various
gaseous forms (N2, N2O) which, as we shall see, provides a
biogeochemical linkage between the ocean and atmosphere.
Element
Nitrogen
Oxidation State
N (+V)
N (+III)
N (O)
N (-III)
Species
NO3NO2N2
NH3, NH4+
Sulfur
S (+VI)
S (+II)
S (O)
S(-II)
Fe (+III)
Fe (+II)
SO42S2O32Sº
H2S, HS-, S2Fe3+
Fe2+
Mn (+VI)
Mn (+IV)
Mn (+III)
Mn (+II)
MnO42MnO2 (s)
MnOOH (s)
Mn2+
Iron
Manganese
Nitrogen in the aquatic system
Includes
DISSOLVED and
particulate, mostly
dissolved!
(D/P = 0.7μm filter)
NO3-
Dominates N-cycle
Tg = 1012 g
The nitrogen cycle
The marine nitrogen cycle
Photic Zone
Aphotic Zone
(1% light level)
Nitrogen fixing planctonic organism
Trichodesmium can provide up to
50% of new production!!!
1 mm
Trichodesmium
(cyanobacteria)
• Cyanobacteria are aquatic and
photosynthetic.
• More than 3.5 billion years old
• One of the largest and most
important groups of bacteria on earth.
Involves Fe and Mo (enzyme
Nitrogenase), thus iron and/or
molybdenum may be a limiting
factor in marine nitrogen fixation.
Nitrogen fixing planctonic organism
Symbioses
10 µm
Symbioses between
Richelia intracellularis and
different Diatom species
• The endosymbiont Richelia is a
cyanobacterium
• Richelia can cover complete Ndemand of host diatom cells
Involves Fe and Mo (enzyme
Nitrogenase), thus iron may be a
limiting factor in marine nitrogen
fixation (micronutrients).
The nitrogen cycle- N2-fixation
N2-fixation: energetically expensive
process
N2 + 8H+ + 8e- + 16ATP →
2NH3 + H2 + 16ADP + 16Pi
N2 → NH4+ → various types of
organic amines
Anabaena sp.
Abbildung aus Brock
CO2 + H2O
→
CH2O + O2↑
Marine N-Budget
Sources
Human Impact
on Global
Nitrogen Fixation
Fertilizer Production
Modern Haber-Bosch Equation:
3 CH4 + 2 N2 +3 O2 → 4 NH3 + 3 CO2
Combustion:
N2 + O2 + H2O → NH3 + NO3
Bloom in SUMMER
Increased P and N input
by fertilizers and detergents
Redfield Ratio (1963): 106 C :16 N : 1 P
+++primary production
106CO2 + 16NO3- + HPO42- + 122H2O + 18 H+
→ (CH2O)106(NH3)16(H3PO4) + 138O2·
Incorporation of these elements in photosynthesis and growth
Toxizität von Blaualgen
In die Schlagzeilen der Zeitungen geraten vor allem Cyanobakterien aus
Süßgewässern (Seen), wenn sie mit dem Wasser getrunken werden und durch
die in ihnen enthaltenen Toxine Säugetiere (Kühe, Hunde) zu Tode kommen. Aber
auch die Cyanobakterien in der Ostsee können toxisch sein.
So mußten im Sommer 2001 Teile der deutschen Ostseestrände aufgrund
hoher Blaualgenkonzentrationen gesperrt werden. Die in der Ostsee
vorkommenden fädigen Cyanobakterien (Nodularia spumigena, Aphanizomenon
flos-aquae, Anabaena sp.) können toxisch sein, sie sind es jedoch nicht immer.
Ihre hochpotenten Gifte (Cyanotoxine) und Allergene ähneln Nervengiften.
So kann Aphanizomenon flos-aquae
sogenannte Anatoxine produzieren, deren
Wirkung den Nervengiften Tabun und
Sarin ähnlich ist. Nodularia spumigena
kann das Nodularin produzieren, ein
hochwirksames Lebergift, daß für
Säugetiere, ähnlich dem Gift des
Knollenblätterpilzes, tödlich sein kann.
Anabaena sp.
The nitrogen cycle - Primary Production
Primary Production
(Photosynthese):
106CO2 + 16NO3- + HPO42- + 122H2O + 18 H+
→ (CH2O)106(NH3)16(H3PO4) + 138O2
NO3- reductase (assimilatory)
NO3- → NO2- → NH4+ → OMRR
N2-fixation
N2 → NH4+ → organic amines
The nitrogen cycle - Ammonification
Remineralization or
Ammonification:
• Common to all organisms
• Accomplished under high and
low O2 conditions as well as
anoxic conditions
peptides (deamination) → NH4+
Water column
Effingham Inlet
(Anoxic Fjord in
British Columbia)
oxic
anoxic
anoxic
oxic
oxic
Ingall et al., 2005
• Ammonium stable under anoxic conditions
• rapidly recycled and converted to
organic-N and oxidized to NO3- under
oxic conditions
The marine nitrogen cycle
oxic
Photic Zone
anoxic
Aphotic Zone
(1% light level)
SO42-
The nitrogen cycle - Nitrification
Mediated by bacterial consortia
2) NO2- → NO3- Nitrobacter sp.
1) NH4+ → (N2O) → NO2- Nitrosomonas sp.
Nitrosococcus
The nitrogen cycle – Nitrification
Experiment: suspension of diatoms (phytoplancton) in seawater
dark
Respiration (NH4-N) – Nitrification(NO2-N → NO3-N)
dark – light – dark
Respiration (NH4-N) – Assimilation (NH4-N → org.-N) –
Respiration (NH4-N) – Nitrification(NO2-N → NO3-N)
The nitrogen cycle - Denitrification
Denitrification (dissimilatory)
NO3- → NO2- → (N2O) → N2
Complete process:
4HNO3 + 5CH2O →
5CO2 + 7H2O + 2N2↑
Nitrate used as terminal e-acceptor for organic matter
degradation by organisms under
suboxic conditions.
Major sink for N – gas exchange
with atmosphere
Remember: Nitrate generated by
the suite of ammonification and
nitrification
Bloom in SUMMER
Nitrogen/phosphors ratio in surface water in WINTER
N-limitation by
Denitrification
(NO3- → N2↑)
Increased P and N input
by fertilizers and detergents
Redfield Ratio (1963): 106 C :16 N : 1 P
+++primary production
106CO2 + 16NO3- + HPO42- + 122H2O + 18 H+
→ (CH2O)106(NH3)16(H3PO4) + 138O2·
Incorporation of these elements in photosynthesis and growth
The nitrogen cycle - Denitrification
•
Denitrification in suband anoxic waters and
sediments
•
Nitrate – Nitrite – N2
O2 Minimum Zones
Experiment:
PVC-Container with water from the oxygen minimum
layer of the northeastern tropical Pacific
Sequence: loss of oxygen,
production of nitrite (NO2-) from nitrate (NO3-),
and final loss of nitrite (reduction to N2↑)
The nitrogen cycle - Denitrification
Experiment:
PVC-Container with water from the oxygen minimum
layer of the northeastern tropical Pacific
Sequence: loss of oxygen,
production of nitrite (NO2-) from nitrate (NO3-),
and final loss of nitrite (reduction to N2↑)
•
Denitrification in suband anoxic waters and
sediments
•
Nitrate – Nitrite – N2
The nitrogen cycle - Denitrification
O2 Minimum Zones
PP, RR
16N:1P
EXP
NO3
OBS
NO3
EXP
NO3
OBS
NO3
OBS
O2
OBS
O2
OBS NO3- is what is OBServed (or measured)
EXP NO3- is what is expected EXPected
Redfield Ratio = 106C : 16N : 1P (calculated conc. P * 16)
→ Difference is due to denitrification
Marine N-Budget
Dominant removal for P? Burial somewhere in sediments!
Dominant removal for N? Not burial! Denitrification!
The marine nitrogen cycle
Photic Zone
Aphotic Zone
(1% light level)
All Parts of N-Cycle
observed in a water column
O2 Minimum Layer
photic
zone
• Primary Production
• Nitrification
• Denitrification
Denitrification by
aerobic bacteria is not
everything!!!
Anammox Bacteria
Anoxic Ammonia Oxidation
NH4+ + NO2- → N2 + 2H2O
a
b
Anaerobic ammonium oxidation
by
Anammox Bacteria
in the Black Sea
b) FISH. Red cells = anammox
a) Simplified marine nitrogen cycle
including the anammox ‚sink‘.
N2
Anoxic Ammonia Oxidation
[14N]nitrite +
[15N]ammonium
NH4+ + NO2- → N2 + 2H2O
c) Chemical zoning and distribution of
Anammox indicators across the Black Sea
Kypers et al. 2003, Nature
Marine N-Budget
plus Anammox !!!
Take home points
¾
Many different oxidation states (+V to –III), gas forms N2 and N2O
¾
Sources: river discharge, rain and dry depositions, N2-fixation
¾
Sinks: sedimentation and denitrification and Anammox
¾
Marine Nitrogen Cycle:
¾Primary Production: NO3- reduction and N2-fixation
¾Respiration: Ammonification, Nitrification, Denitrification
¾Zonation
of Processes around Water Column O2 Minima
Sauerstoffverteilung und die
Nährstoffsenken
N-Verlust durch
Denitrification
(NO3- → N2↑ )
P-Verlust durch
Sedimentakkumulation
Das Umkippen eines Sees bedeutet, dass das Phosphat, als der
begrenzende Nährstoff, wegen eines dauerhaften
Sauerstoffmangels nicht mehr als Eisen(III)-phosphat am
Seeboden abgelegt werden kann, sondern vollständig und
düngewirksam im Wasser gelöst bleibt .
Aus Wikipedia
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Feedbacks
• Oxygen on Phosphate
• Oxygen on Denitrification
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Sedimentary P-cycling
35
Redox governance of the phosphate reflux
Phosphat fest gebunden
in Fe(III)- Verbindungen
Phosphat mobilisiert
in Fe (II)-Verbindungen
Fig. from C, Bernes, Monitor 19, 2005
Positive feedback between redox
conditions and productivity
=> Redox conditions and marine productivity may change
dramatically under P-limitation
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Sedimentary N-Cycling
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The nitrogen cycle
- Denitrification
Denitrification (dissimilatory)
NO3- → NO2- → (N2O) → N2
Complete process:
4HNO3 + 5CH2O →
5CO2 + 7H2O + 2N2↑
Nitrate used as terminal e-acceptor for organic matter
degradation by organisms under
suboxic conditions.
Major sink for N – gas exchange
with atmosphere
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Feedbacks between sedimentary redox
conditions and marine productivity
40
Nitrogen fixation
Trichodesmium can provide up to
50% of new production!!!
1 mm
Trichodesmium
(cyanobacteria)
• Cyanobacteria are aquatic and
photosynthetic.
• More than 3.5 billion years old
• One of the largest and most
important groups of bacteria on earth.
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