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The Nitrogen cycle

Element Oxidation State Species Nitrogen N (+V)

N (+III) N (O) N (-III)

NO3-

NO2-

N2

NH3, NH4+

Sulfur S (+VI)

S (+II) S (O) S(-II)

SO42-

S2O32-

Sº H2S, HS-, S2-

Iron Fe (+III) Fe (+II)

Fe3+

Fe2+

Manganese Mn (+VI) Mn (+IV) Mn (+III) Mn (+II)

MnO42-

MnO2 (s) MnOOH (s) Mn2+

Nitrogen cycleUnlike phosphorus (PO4

3- = +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.

Includes DISSOLVED and particulate, mostly

dissolved!(D/P = 0.7μm filter)

NO3- Dominates N-cycle

Tg = 1012 g

Nitrogen in the aquatic system

The nitrogen cycle

The marine nitrogen cycle

Photic Zone

Aphotic Zone(1% light level)

Nitrogen fixing planctonic organism

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.

1 mm

Involves Fe and Mo (enzyme Nitrogenase), thus iron and/or molybdenum may be a limiting factor in marine nitrogen fixation.

Trichodesmium can provide up to50% of new production!!!

Nitrogen fixing planctonic organism

Symbioses betweenRichelia intracellularis anddifferent Diatom species

Involves Fe and Mo (enzyme Nitrogenase), thus iron may be a limiting factor in marine nitrogen fixation (micronutrients).

• The endosymbiont Richelia is a cyanobacterium

• Richelia can cover complete N-demand of host diatom cells

10 µm

Symbioses

N2-fixation: energetically expensive process

N2 + 8H+ + 8e- + 16ATP →2NH3 + H2 + 16ADP + 16Pi

N2 → NH4+ → various types of

organic amines

The nitrogen cycle- N2-fixation

Abbildung aus BrockCO2 + H2O →

CH2O + O2↑

Anabaena sp.

Marine N-BudgetSources

Modern Haber-Bosch Equation:

3 CH4 + 2 N2 +3 O2 → 4 NH3 + 3 CO2

Combustion:

N2 + O2 + H2O → NH3 + NO3

Human Impacton Global

Nitrogen Fixation

Fertilizer Production

Redfield Ratio (1963): 106 C :16 N : 1 P

106CO2 + 16NO3- + HPO4

2- + 122H2O + 18 H+

→ (CH2O)106(NH3)16(H3PO4) + 138O2·

Incorporation of these elements in photosynthesis and growth

Increased P and N inputby fertilizers and detergents

+++primary production

Bloom in SUMMER

Toxizität von BlaualgenIn 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 kann Aphanizomenon flos-aquae sogenannte Anatoxine produzieren, deren Wirkung den Nervengiften Tabun und Sarin ähnlich ist. Nodularia spumigenakann das Nodularin produzieren, ein hochwirksames Lebergift, daß für Säugetiere, ähnlich dem Gift des Knollenblätterpilzes, tödlich sein kann.

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.

Anabaena sp.

Primary Production (Photosynthese):

106CO2 + 16NO3- + HPO4

2- + 122H2O + 18 H+

→ (CH2O)106(NH3)16(H3PO4) + 138O2

NO3- reductase (assimilatory)

NO3- → NO2

- → NH4+ → OMRR

N2-fixationN2 → NH4

+ → organic amines

The nitrogen cycle - Primary Production

Remineralization or Ammonification:

• Common to all organisms• Accomplished under high and low O2 conditions as well as anoxic conditions

peptides (deamination) → NH4+

The nitrogen cycle - Ammonification

Ingall et al., 2005

Effingham Inlet

(Anoxic Fjord inBritish Columbia)

oxic

anox

icWater column

oxicanoxic

oxic

• Ammonium stable under anoxic conditions

• rapidly recycled and converted toorganic-N and oxidized to NO3

- underoxic conditions

The marine nitrogen cycle

Photic Zone

Aphotic Zone(1% light level)

oxicanoxic

SO42-

The nitrogen cycle - Nitrification

Mediated by bacterial consortia

2) NO2- → NO3

- Nitrobacter sp.

1) NH4+ → (N2O) → NO2

- Nitrosomonas sp.Nitrosococcus

dark

dark – light – dark

The nitrogen cycle – NitrificationExperiment: suspension of diatoms (phytoplancton) in seawater

Respiration (NH4-N) – Nitrification(NO2-N → NO3-N)

Respiration (NH4-N) – Assimilation (NH4-N → org.-N) –

Respiration (NH4-N) – Nitrification(NO2-N → NO3-N)

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

The nitrogen cycle - Denitrification

Redfield Ratio (1963): 106 C :16 N : 1 P

106CO2 + 16NO3- + HPO4

2- + 122H2O + 18 H+

→ (CH2O)106(NH3)16(H3PO4) + 138O2·

Incorporation of these elements in photosynthesis and growth

N-limitation byDenitrification(NO3

- → N2↑)

Increased P and N inputby fertilizers and detergents

+++primary production

Nitrogen/phosphors ratio in surface water in WINTERBloom in SUMMER

• Denitrification in sub-and anoxic waters and sediments

• Nitrate – Nitrite – N2

The nitrogen cycle - Denitrification

Experiment:

PVC-Container with water from the oxygen minimumlayer of the northeastern tropical Pacific

Sequence: loss of oxygen,production of nitrite (NO2-) from nitrate (NO3-),and final loss of nitrite (reduction to N2↑)

O2 Minimum Zones

• Denitrification in sub-and anoxic waters and sediments

• Nitrate – Nitrite – N2

The nitrogen cycle - Denitrification

Experiment:

PVC-Container with water from the oxygen minimumlayer of the northeastern tropical Pacific

Sequence: loss of oxygen,production of nitrite (NO2-) from nitrate (NO3-),and final loss of nitrite (reduction to N2↑)

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

The nitrogen cycle - Denitrification

O2 Minimum Zones PP, RR16N:1P

OBSO2

OBSO2

OBSNO3OBS

NO3

EXPNO3

EXPNO3

Dominant removal for P? Burial somewhere in sediments!

Dominant removal for N? Not burial! Denitrification!

Marine N-Budget

The marine nitrogen cycle

Photic Zone

Aphotic Zone(1% light level)

• Primary Production• Nitrification• Denitrification

All Parts of N-Cycle observed in a water column

photiczone

O2

Min

imum

Lay

er

Denitrification by aerobic bacteria is not everything!!!

Anammox Bacteria

Anoxic Ammonia Oxidation

NH4+ + NO2

- → N2 + 2H2O

Anaerobic ammonium oxidationby

Anammox Bacteriain the Black Sea

a) Simplified marine nitrogen cycleincluding the anammox ‚sink‘.

b) FISH. Red cells = anammox

a b

c) Chemical zoning and distribution ofAnammox indicators across the Black Sea Kypers et al. 2003, Nature

[14N]nitrite +[15N]ammoniumAnoxic Ammonia Oxidation

NH4+ + NO2

- → N2 + 2H2O

N2

plus Anammox !!!

Marine N-Budget

Take home points

Many different oxidation states (+V to –III), gas forms N2 and N2O

Sources: river discharge, rain and dry depositions, N2-fixation

Sinks: sedimentation and denitrification and Anammox

Marine Nitrogen Cycle:

Primary Production: NO3- reduction and N2-fixation

Respiration: Ammonification, Nitrification, Denitrification

Zonation of Processes around Water Column O2 Minima

Sauerstoffverteilung und die Nährstoffsenken

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

N-Verlust durchDenitrification(NO3

- → N2↑ )

P-Verlust durchSediment-

akkumulation

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Feedbacks

• Oxygen on Phosphate• Oxygen on Denitrification

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Sedimentary P-cycling

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Redox governance of the phosphate reflux

Fig. from C, Bernes, Monitor 19, 2005

Phosphat fest gebunden in Fe(III)- Verbindungen

Phosphat mobilisiert in Fe (II)-Verbindungen

Positive feedback between redox conditions and productivity

=> Redox conditions and marine productivity may change dramatically under P-limitation 37

Sedimentary N-Cycling

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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

The nitrogen cycle - Denitrification

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Feedbacks between sedimentary redox conditions and marine productivity

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Nitrogen fixation

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.

1 mm

Trichodesmium can provide up to50% of new production!!!

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