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Biogeochemistry > L8 - The Nitrogen cycle > Flashcards

L8 - The Nitrogen cycle Flashcards

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1
Q

What is the difference between a feedback and a forcing in the Earth system?

A

A forcing (e.g., burning fossil fuels) is an external perturbation, while a feedback is an internal process that responds to changes in the system.

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2
Q

What is a negative feedback?

A

A response that counteracts the change that caused it.

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3
Q

What is a positive feedback?

A

A response that reinforces the change that caused it.

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4
Q

can feedbacks cause runaway effects

A

Generally, no—positive feedbacks do not usually cause runaway effects but can influence the system’s equilibrium.

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5
Q

What is a tipping point in the Earth system?

A

The point at which a system can switch between two different equilibrium states due to complex feedbacks.

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6
Q

What initiated recent ice ages according to the presentation?

A

Milankovitch cycles (changes in Earth’s orbit and rotation).

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7
Q

Why weren’t Milankovitch cycles alone sufficient to cause ice ages?

A

The changes in solar flux were too subtle; positive carbon cycle feedbacks amplified the climate changes.

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8
Q

In the example of fast land feedbacks, what happens as surface temperature increases?

A

Snow cover decreases, reducing albedo, increasing absorption of solar radiation, and further warming the surface.

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9
Q

How does increasing temperature affect soil moisture and evapotranspiration?

A

It decreases soil moisture, reduces evapotranspiration, and can lead to surface warming.

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10
Q

How does increasing CO₂ affect plant stomata and atmospheric CO₂?

A

Plants reduce stomatal size to limit water loss, enhancing carbon assimilation, leading to a negative feedback on atmospheric CO₂.

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11
Q

How does reducing stomatal size also impact surface temperature?

A

It reduces evapotranspiration, leading to surface warming.

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12
Q

What are the main anthropogenic sources of CO₂ mentioned?

A

Burning fossil fuels, cement production, and agricultural practices.

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13
Q

What evidence shows that fossil fuel combustion is mainly responsible for increased CO₂?

A

A slight reduction in atmospheric oxygen and changes in carbon isotope ratios.

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14
Q

How does agriculture affect the CO₂ cycle?

A

Crops take up carbon during growth but release it back to the atmosphere during harvest and respiration.

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15
Q

Why is wood considered a ‘carbon-neutral’ fuel?

A

If trees are replanted after harvesting, the carbon cycle remains balanced.

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16
Q

How does slash-and-burn agriculture impact the carbon cycle?

A

it releases carbon to the atmosphere without restoring an equivalent carbon store.

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17
Q

What is the effect of eutrophication on carbon capture?

A

It can increase biological activity temporarily but does not create large enough stores to permanently capture carbon.

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18
Q

What is NEP (Net Ecosystem Productivity)?

A

NEP = Gross Primary Productivity – (Plant and Soil Respiration).

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19
Q

How can warming affect terrestrial NPP (Net Primary Production)?

A

It may increase NPP, but increased soil turnover could return carbon back to the atmosphere.

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20
Q

What is the CO₂ fertilization effect?

A

Higher CO₂ levels increase plant growth by enhancing photosynthesis.

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21
Q

What limits the CO₂ fertilization effect?

A

Availability of nutrients like nitrogen and phosphorus.

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22
Q

How does global warming affect tropical rainfall and NPP?

A

It likely reduces tropical rainfall, leading to suppression of NPP.

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23
Q

How does increased tropospheric ozone impact plant growth?

A

It reduces plant growth, lowering NPP.

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24
Q

What is the soil respiration feedback?

A

Higher temperatures increase soil respiration, releasing more CO₂ and enhancing warming.

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25
What is the permafrost feedback?
Warming decreases permafrost, increases wetlands, and releases more CO₂ and CH₄, enhancing warming.
26
How does fire feedback, precipitation-limited, affect carbon release?
Less precipitation increases fire frequency and extent, releasing more CO₂ and CH₄.
27
How does fire feedback, biomass-limited, affect carbon release?
More biomass due to warming and CO₂ increase leads to more fires and CO₂ release.
28
How does CO₂ fertilization feedback act as a carbon sink?
Enhanced photosynthesis increases biomass carbon storage, reducing atmospheric CO₂ and warming.
29
Why are oceans an important sink for atmospheric CO₂?
Oceans dissolve and transfer about 90 PgC per year to deep water and have a buffering capacity due to dissolved carbonate.
30
What chemical reactions govern CO₂ dissolution in seawater?
CO₂ (g) + H₂O ↔ CO₂·H₂O CO₂·H₂O ↔ H⁺ + HCO₃⁻ HCO₃⁻ ↔ H⁺ + CO₃²⁻
31
How does temperature affect CO₂ solubility in the ocean?
CO₂ solubility decreases as temperature increases.
32
How does ocean acidification occur?
CO₂ reacts with water to form HCO₃⁻ and H⁺, lowering pH.
33
What is the main buffering reaction in seawater?
H⁺ + CO₃²⁻ → HCO₃⁻ Overall: CO₂ + CO₃²⁻ + H₂O → 2HCO₃⁻
34
What happens to carbonate ion concentrations as ocean acidification increases?
Carbonate ion concentrations decrease.
35
How does reduced carbonate affect marine life?
It limits shell and coral formation (calcification).
36
What is the impact of reduced carbonate on deep ocean solid carbonates?
It increases the dissolution of solid carbonates, making carbonate more available to surface waters.
37
How does ocean acidification impact the ocean's ability to absorb CO₂?
It reduces the ocean's capacity to take up additional CO₂.
38
What is the organic carbon pump?
It is the gravitational fall of dead biological material (POC) transporting carbon to the deep ocean (~11 PgC/yr).
39
How would increased marine NPP affect the organic carbon pump?
It would enhance the organic carbon pump, acting as a negative feedback to climate change.
40
What is the carbonate counter-pump?
Increased marine NPP also removes carbonate through shell formation, reducing buffering and acting as a positive feedback
41
How would increased marine NPP affect the organic carbon pump?
It would enhance the organic carbon pump, acting as a negative feedback to climate change.
42
How does increased temperature affect ocean circulation and carbon uptake?
It stabilizes the surface ocean, reducing mixing and CO₂ uptake, but can increase the efficiency of the biological pump.
43
What is the pCO₂ buffer factor feedback?
Higher atmospheric CO₂ increases ocean pCO₂, reducing the ocean's capacity to absorb additional CO₂.
44
What is the CO₂ temperature dissociation feedback?
Increased temperature and CO₂ cause more dissociation into HCO₃⁻, enhancing CO₂ uptake and leading to cooling.
45
What is the CO₂ temperature solubility feedback?
Warming reduces CO₂ solubility, leading to more outgassing and increased atmospheric CO₂.
46
What is the inorganic carbon buffering feedback?
As atmospheric CO₂ rises, ocean buffering increases CO₂ uptake and short-term carbon retention, slowing atmospheric CO₂ increases.
47
What limits the effectiveness of the organic carbon pump?
Nutrient limitations, re-release of carbon by consumers, and remineralization processes in deeper waters.
48
What specific biological impacts are hard to predict with ocean warming and acidification?
Events like coral bleaching.
49
What is the most abundant gas in the atmosphere and the biggest nitrogen reservoir?
N₂ (elemental nitrogen).
50
Why is elemental nitrogen so inert?
Because of its very strong triple bond (9.75 eV), which requires large energy or a catalyst to break
51
What are reactive nitrogen species (Nᵣ)?
Nitrogen compounds formed once the N₂ bond is broken, including NH₃, NH₄⁺, NO, NO₂⁻, HNO₃, N₂O, HONO, PAN, and organic N compounds.
52
What forms of nitrogen are important in biochemistry?
Amines, amides, amino acids, and proteins
53
What are reactive nitrogen species (Nᵣ)?
Nitrogen compounds formed once the N₂ bond is broken, including NH₃, NH₄⁺, NO, NO₂⁻, HNO₃, N₂O, HONO, PAN, and organic N compounds.
54
What forms of nitrogen are important in biochemistry?
Amines, amides, amino acids, and proteins.
55
How is nitrogen naturally fixed from the atmosphere?
Through biological nitrogen fixation (BNF) by microbes and NOₓ production by lightning.
56
What state must nitrogen be in for plants to absorb it?
Either as ammonium (NH₄⁺, -3 oxidation state) or nitrate (NO₃⁻, +5 oxidation state).
57
What is biological nitrogen fixation (BNF)?
The conversion of atmospheric N₂ into ammonium (NH₄⁺) by certain bacteria and algae.
58
Why must nitrogen fixation occur anaerobically?
Because the reactions are high-energy and reductive, and oxygen would interfere.
59
Name an important group of symbiotic nitrogen-fixing bacteria.
Rhizobium, found on the roots of legumes like clover and soybeans.
60
What role do free-living nitrogen fixers play?
They fix nitrogen independently of plant hosts in soil or water (e.g., cyanobacteria).
61
What happens to nitrogen after organisms die?
Decomposers convert nitrogen in dead tissue back into forms usable by the biosphere.
62
What is nitrification?
The oxidation of ammonium (NH₄⁺) to nitrate (NO₃⁻) by nitrifying bacteria.
63
In what environments does nitrification occur?
Oxygen-rich environments like surface soils and flowing waters
64
What is a consequence of nitrification on soil?
It can cause soil acidification and nitrate leaching.
65
What is denitrification?
The anaerobic process where nitrate (NO₃⁻) is converted back to N₂ gas.
66
What gases are produced as byproducts during denitrification?
Nitric oxide (NO) and nitrous oxide (N₂O).
67
Why is denitrification important in the nitrogen cycle?
It removes nitrogen from ecosystems by returning it to the atmosphere as N₂.
68
What is ammonification?
The breakdown of nitrogenous biological waste into ammonia by anaerobic bacteria and fungi.
69
What is remineralisation?
The oxidation of organic material in the presence of oxygen, releasing inorganic nitrogen and CO₂.
70
How do plants assimilate nitrogen?
By absorbing NO₃⁻ and NH₄⁺ and converting them internally into amino acids.
71
Where does nitrate reduction mostly occur in plants?
In the shoots, after transport via the xylem.
72
What are the major natural reservoirs of nitrogen?
Atmosphere (N₂) Hydrosphere (NH₄⁺, NO₂⁻, NO₃⁻) Pedosphere (soils) Biosphere (organic nitrogen compounds)
73
What is the Haber-Bosch process?
The industrial synthesis of ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂) using an iron catalyst at high temperature and pressure.
74
Why was the Haber-Bosch process crucial during WWI?
Germany needed nitric acid for munitions after losing access to Chilean sodium nitrate
75
What are the main industrial uses of ammonia produced by Haber-Bosch?
Manufacturing fertilizers like ammonium nitrate, ammonium sulfate, and urea.
76
How does overfertilization affect the atmosphere?
It releases ammonia (NH₃) and promotes microbial production of NO and N₂O gases.
77
Why is nitrous oxide (N₂O) a concern for the environment?
It is a greenhouse gas that persists in the troposphere and disrupts stratospheric ozone chemistry.
78
How can increased fertilizer use affect the carbon cycle?
By promoting net primary production (NPP) and increasing CO₂ sequestration in the biosphere
79

Biogeochemistry (11 decks)

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