The Nitrogen cycle. www-ocean.tamu.edu/.../ QD4.3/joyechart-4.3.html

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1 The Nitrogen cycle www-ocean.tamu.edu/.../ QD4.3/joyechart-4.3.html

2 Nitrogen cycle Unlike phosphorus (PO 4 3- = +V), nitrogen displays many different oxidation states (+V to III) in seawater. Nitrogen exists in various gaseous forms (N 2, N 2 O) which, as we shall see, provides a biogeochemical linkage between the ocean and atmosphere. Element Oxidation State Species Nitrogen N (+V) N (+III) N (O) N (-III) - NO 3 - NO 2 N 2 + NH3, NH 4 Sulfur Iron Manganese S (+VI) S (+II) S (O) S(-II) Fe (+III) Fe (+II) Mn (+VI) Mn (+IV) Mn (+III) Mn (+II) 2- SO 4 2- S 2 O 3 Sº H2S, HS -, S 2- Fe 3+ Fe 2+ MnO 4 2- MnO2 (s) MnOOH (s) Mn 2+

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5 Nitrogen in the aquatic system Includes DISSOLVED and particulate, mostly dissolved! (D/P = 0.7μm filter) NO 3 - Dominates N-cycle Tg = g

6 The nitrogen cycle

7 The marine nitrogen cycle Photic Zone Aphotic Zone (1% light level)

8 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.

9 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 N- demand of host diatom cells Involves Fe and Mo (enzyme Nitrogenase), thus iron may be a limiting factor in marine nitrogen fixation (micronutrients).

10 The nitrogen cycle- N 2 -fixation N 2 -fixation: energetically expensive process N 2 + 8H + + 8e ATP 2NH 3 + H ADP + 16P i N 2 NH 4+ various types of organic amines Anabaena sp. CO 2 Abbildung + H 2 O aus Brock CH 2 O + O 2

11 Marine N-Budget Sources

12 Human Impact on Global Nitrogen Fixation Modern Haber-Bosch Equation: Fertilizer Production 3 CH N 2 +3 O 2 4 NH CO 2 Combustion: N 2 + O 2 + H 2 O NH 3 + NO 3

13 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- + HPO H2O + 18 H+ (CH2O)106(NH3)16(H3PO4) + 138O2 Incorporation of these elements in photosynthesis and growth

14 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.

15 The nitrogen cycle - Primary Production Primary Production (Photosynthese): 106CO NO 3- + HPO H 2 O + 18 H + (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) + 138O 2 NO 3- reductase (assimilatory) NO 3- NO 2- NH 4 + OM RR N 2 -fixation N 2 NH 4+ organic amines

16 The nitrogen cycle - Ammonification Remineralization or Ammonification: Common to all organisms Accomplished under high and low O 2 conditions as well as anoxic conditions peptides (deamination) NH 4 +

17 Effingham Inlet Water column (Anoxic Fjord in British Columbia) oxic Ingall et al., 2005 oxic anoxic oxic anoxic Ammonium stable under anoxic conditions rapidly recycled and converted to organic-n and oxidized to NO 3- under oxic conditions

18 The marine nitrogen cycle Photic Zone Aphotic Zone (1% light level) SO 4 2- oxic anoxic

19 The nitrogen cycle - Nitrification Mediated by bacterial consortia 2) NO 2- NO 3 - Nitrobacter sp. 1) NH 4 + (N 2 O) NO 2- Nitrosomonas sp. Nitrosococcus

20 The nitrogen cycle Nitrification Experiment: suspension of diatoms (phytoplancton) in seawater dark Respiration (NH 4 -N) Nitrification(NO 2 -N NO 3 -N) dark light dark Respiration (NH 4 -N) Assimilation (NH 4 -N org.-n) Respiration (NH 4 -N) Nitrification(NO 2 -N NO 3 -N)

21 The nitrogen cycle - Denitrification Denitrification (dissimilatory) NO 3- NO 2- (N 2 O) N 2 Complete process: 4HNO 3 + 5CH 2 O 5CO 2 + 7H 2 O + 2N 2 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

22 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- + HPO H2O + 18 H+ (CH2O)106(NH3)16(H3PO4) + 138O2 Incorporation of these elements in photosynthesis and growth

23 The nitrogen cycle - Denitrification Denitrification in suband anoxic waters and sediments Nitrate Nitrite N 2 O 2 Minimum Zones Experiment: PVC-Container with water from the oxygen minimum layer of the northeastern tropical Pacific Sequence: loss of oxygen, production of nitrite (NO 2 -) from nitrate (NO 3 -), and final loss of nitrite (reduction to N 2 )

24 The nitrogen cycle - Denitrification Denitrification in suband anoxic waters and sediments Nitrate Nitrite N 2 Experiment: PVC-Container with water from the oxygen minimum layer of the northeastern tropical Pacific Sequence: loss of oxygen, production of nitrite (NO 2 -) from nitrate (NO 3 -), and final loss of nitrite (reduction to N 2 )

25 The nitrogen cycle - Denitrification O 2 Minimum Zones PP, RR 16N:1P EXP NO 3 EXP NO 3 OBS O 2 OBS NO 3 OBS O 2 OBS NO 3 OBS NO 3- is what is OBServed (or measured) EXP NO 3- is what is expected EXPected Redfield Ratio = 106C : 16N : 1P (calculated conc. P * 16) Difference is due to denitrification

26 Marine N-Budget Dominant removal for P? Burial somewhere in sediments! Dominant removal for N? Not burial! Denitrification!

27 The marine nitrogen cycle Photic Zone Aphotic Zone (1% light level)

28 photic zone All Parts of N-Cycle observed in a water column O 2 Minimum Layer Primary Production Nitrification Denitrification

29 Denitrification by aerobic bacteria is not everything!!! Anammox Bacteria Anoxic Ammonia Oxidation NH 4+ + NO 2 - N 2 + 2H 2 O

30 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. N 2 Anoxic Ammonia Oxidation [14N]nitrite + [15N]ammonium NH 4+ + NO 2 - N 2 + 2H 2 O c) Chemical zoning and distribution of Anammox indicators across the Black Sea Kypers et al. 2003, Nature

31 Marine N-Budget plus Anammox!!!

32 Take home points Many different oxidation states (+V to III), gas forms N 2 and N 2 O Sources: river discharge, rain and dry depositions, N 2 -fixation Sinks: sedimentation and denitrification and Anammox Marine Nitrogen Cycle: Primary Production: NO 3- reduction and N 2 -fixation Respiration: Ammonification, Nitrification, Denitrification Zonation of Processes around Water Column O 2 Minima

33 Sauerstoffverteilung und die Nährstoffsenken N-Verlust durch Denitrification (NO 3- N 2 ) 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 33

34 Feedbacks Oxygen on Phosphate Oxygen on Denitrification 34

35 Sedimentary P-cycling 35

36 Redox governance of the phosphate reflux Phosphat fest gebunden Phosphat mobilisiert in Fe(III)- Verbindungen in Fe (II)-Verbindungen Fig. from C, Bernes, Monitor 19, 2005

37 Positive feedback between redox conditions and productivity => Redox conditions and marine productivity may change dramatically under P-limitation 37

38 Sedimentary N-Cycling 38

39 The nitrogen cycle - Denitrification Denitrification (dissimilatory) NO 3- NO 2- (N 2 O) N 2 Complete process: 4HNO 3 + 5CH 2 O 5CO 2 + 7H 2 O + 2N 2 Nitrate used as terminal e - - acceptor for organic matter degradation by organisms under suboxic conditions. Major sink for N gas exchange with atmosphere 39

40 Feedbacks between sedimentary redox conditions and marine productivity 40

41 Nitrogen fixation 1 mm Trichodesmium can provide up to 50% of new production!!! 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. 41

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