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The Nitrogen Cycle

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The Nitrogen Cycle The Nitrogen cycle www-ocean.tamu.edu/.../ QD4.3/joyechart-4.3.html Nitrogen cycle 3- Unlike phosphorus (PO4 = +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 Oxidation State Species - Nitrogen N (+V) NO3 - N (+III) NO2 N (O) N2 + N (-III) NH3, NH4 2- Sulfur S (+VI) SO4 2- S (+II) S2O3 S (O) Sº - 2- S(-II) H2S, HS , S 3+ Iron Fe (+III) Fe 2+ Fe (+II) Fe 2- Manganese Mn (+VI) MnO4 Mn (+IV) MnO2 (s) Mn (+III) MnOOH (s) Mn (+II) Mn2+ Nitrogen in the aquatic system Includes DISSOLVED and particulate, mostly dissolved! (D/P = 0.7μm filter) - Dominates N-cycle NO3 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. Involves Fe and Mo (enzyme • More than 3.5 billion years old Nitrogenase), thus iron and/or • One of the largest and most molybdenum may be a limiting important groups of bacteria on earth. 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 Involves Fe and Mo (enzyme Nitrogenase), thus iron may be a • Richelia can cover complete N- limiting factor in marine nitrogen demand of host diatom cells 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. CO2Abbildung+ H2O aus Brock → 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 - 2- + 106CO2 + 16NO3 + HPO4 + 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): - 2- + 106CO2 + 16NO3 + HPO4 + 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 Effingham Inlet Water column (Anoxic Fjord in British Columbia) oxic anoxic Ingall et al., 2005 oxic oxic • Ammonium stable under anoxic conditions • rapidly recycled and converted to - anoxic organic-N and oxidized to NO3 under oxic conditions The marine nitrogen cycle oxic Photic Zone anoxic Aphotic Zone (1% light level) 2- SO4 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 - 2- + 106CO2 + 16NO3 + HPO4 + 122H2O + 18 H → (CH2O)106(NH3)16(H3PO4) + 138O2· Incorporation of these elements in photosynthesis and growth The nitrogen cycle - Denitrification • Denitrification in sub- and 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 • Denitrification in sub- and anoxic waters and sediments • Nitrate – Nitrite – N2 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 O Minimum Zones PP, RR 2 16N:1P EXP EXP NO3 NO3 OBS NO OBS 3 OBS NO3 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 photic zone Minimum Layer 2 O • 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 [14N]nitrite + Anoxic Ammonia Oxidation [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 P-Verlust durch Denitrification Sediment- - (NO3 → N2↑ ) akkumulation 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 Feedbacks • Oxygen on Phosphate • Oxygen on Denitrification 34 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 37 Sedimentary N-Cycling 38 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 39 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. 41 42.
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