GEOCHEMICAL CYCLES Carbon Reservoir Carbon (gigatons) Percent of - - PowerPoint PPT Presentation

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Dec 09, 2022 546 likes •782 views

GEOCHEMICAL CYCLES Carbon Reservoir Carbon (gigatons) Percent of total carbon on Earth Oceans 38 x 10 3 0.05% (95% is inorganic) Rocks & sediment 75 x 10 6 99.5% (80% is inorganic) Terrestrial biosphere 2 x 10 3 0.003% Aquatic

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GEOCHEMICAL CYCLES

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Carbon

Reservoir Carbon (gigatons) Percent of total carbon on Earth Oceans 38 x 103 (95% is inorganic) 0.05% Rocks & sediment 75 x 106 (80% is inorganic) 99.5% Terrestrial biosphere 2 x 103 0.003% Aquatic biosphere 1-2 0.000002% Fossil fuels 4.2 x 103 0.006% Methane hydrates 104 0.014%

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Carbon

Involving: heterotrophic and autotrophic organisms

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Carbon

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Carbon

Syntrophy is a metabolic process in which two or more organisms cooperate in the degradation of some compound. This is most evident in methanogenesis.

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Nitrogen

Principle form = N2

– Limited use to micro-

rganisms

– Nitrogen fixing bacteria

Ammonia

– Product of nitrogen fixation – Ammonification

Anammox

– Anaerobic oxidation of ammonia – Nitrite as intermediate

Nitrification

– Oxidation of ammonia – Two-step process (ammonia

xidation + nitrite oxidation)

– Sensitive process

Denitrification

– Loss of nitrogen from biosphere – Nitrate  N2

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Nitrogen

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Nitrogen transformation

– Ammonium is readily uptaken and biochemically processed – Nitrate needs to be reduced – Nitrate- and nitrite reductases – Some organisms cannot utilise nitrate/nitrite

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Nitrogen

Nitrogen fixation

– N2 + (at least) 6 ATP  2 NH3 – Some cyanobacteria, Azotobacter, Rhyzobium, Bradyrhizobium – Nitrogenase enzyme – Nitrogenase is irreversibly inhibited by O2 – Specialised structures are utilised to protect nitrogenase -- heterocysts – Requires much energy, exudates from roots facilitate energy supply.

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Nitrogen

Ammonification

– Organic-N  NH4 + CO2 + energy – Under anaerobic conditions, used to be called “putrefication” – wonder why...?

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Nitrogen

Nitrification

– NH3 + 1.5 O2 + CO2  NO2 + H2O + H+ +energy – Nitrosomonas (and a few others) – Ammonia monooxygenase – NO2 + 0.5O2 + CO2  energy + NO3 – Nitrobacter + Nitrospira – May also be done by Crenarchaeota (ammonia oxidising archaea)

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Nitrogen

Anammox

– NH4 + NO2  N2 + 2H2O (hydrazine as intermediate) – Planctomycetee (Brocadia, Kuenenia, Jettenia, Salindua) – Use nitrite as an oxidant (Kuenen & Jetten 2001, ASM news 57:456) – Recently discovered, but may be very important process (65%

f N2 production in Baltic sea)

– Organisms’ doubling time = 2 weeks!

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Nitrogen

Denitrification

– Alternate form of respiration – NO3 NO2 NO N2O  N2 – Many bacteria

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Sulphur

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Sulphur

Sulphide/sulphur oxidation

– Sulphur chemolithotrophs – Thiobacillus, Beggiotoa, many other aerobes – Purple and green phototrophic bacteria (anaerobes)

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Sulphur

Sulphide/sulphur oxidation

– Beggiotoa: H2S + ½ O2  S + H2O + ATP sulphur is stored, then when sulphide depletes: 1.5 O2 + S + H2O  H2SO4 + ATP – Thiobacillus: 2Na2S2O3 + O2  2S + Na2SO4 + ATP

r, 5S + 6NO3
+ 2CO3-  5SO4

2- + 2CO2 + 3N2 + ATP

– Photosynthetic sulphur bacteria: 2CO2 + 2H2O + H2S + light  2(CH2O) + H2SO4

r, CO2 + H2S  2(CH2O) + S

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Sulphur

Sulphur reduction

– Alternate respiration bacteria – Desulfovibrio, Desulfomaculum – SO4

2- + 2(CH2O)  2CO2 + 2H2O + S2- + ATP

– SO4

2- + 4H2  4H2O + S2- + ATP

– S2O3

+ CH3COO- + H+  HS- + 2CO2 + H2O

– They make mud “stink”

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Sulphur

Dimethyl sulphide

– Main gaseous product of sulphur cycle – Marine algae, cyanobacteria, some plants – Chemical defense – “Tidal” smell contributor – Dimethyl sulphide + light  sulphonic acid – Sulphonic acid  H2SO4 + CO2 + energy

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