Lecture 15: Biogeochemical Cycles

Question 1

What is a source vs. sink?

Answer 1

• Source gives the chemical to the reservoir
• Sink receives the chemical from the reservoir

Question 2

What are the reservoirs of carbon?

Answer 2

• Atmospheric CO2
• Oceans (CO2, HCO3-, H2CO3, CO32-)
• Rocks and sediment
• Biosphere (terrestrial and aquatic)
• Fossil fuels

Question 3

Briefly summarize the carbon cycle.

Answer 3

The movement of carbon through the biosphere (atmosphere, ecosphere, hydrosphere, lithosphere)
- Burning fossil fuels puts carbon in the atmosphere
- Atmospheric carbon is absorbed by vegetation, soil, and oceans

Question 4

How do decomposition rates vary in different conditions?

Answer 4

Decomposition rates are faster at higher temperatures

Question 5

What is trophic efficiency?

Answer 5

The efficiency of energy flow between trophic levels in a food chain

Question 6

What is the 10% rule of trophic level transfer?

Answer 6

Each trophic level only give 10% of its energy to the next level
- Uses the other 90% to live, grow, reproduce (lost to the environment as heat)

Question 7

What is primary production and what limits it?

Answer 7

The amount of CO2 converted into organic molecules
- Limited by nutrients

Question 8

What is the ocean acidification equation?

Answer 8

CO2 reacts with water creating acid

Question 9

What are greenhouse gases?

Answer 9

Gases in the earth’s atmosphere that trap heat

Question 10

Give some examples of greenhouse gases.

Answer 10

• Carbon dioxide (CO2)
• Methane (CH4)
• Nitrous oxide (N2O)

Question 11

How is methane produced?

Answer 11

Question 12

How is methane degraded?

Answer 12

Question 13

Microbial methane production and removal
- Who
- What
- Where

Answer 13

1. Production
   - Who: methanogens
   - What: methanogenesis (type of anaerobic respiration)
   - Where: wetlands, guts of ruminants, rice paddies, landfills
2. Removal
   - Who: methanotrophs
   - What: methanotrophy (oxidation of methane)
   Where: soils, freshwater and marine environments, and atmosphere

Question 14

Briefly summarize the nitrogen cycle.

Answer 14

1. Nitrification produces NO3-
   - Nitrosomonas and Nitrobacter
2. Denitrification produces N2
   - Bacillus, Paracoccus, Pseudomonas
3. Nitrogen fixation produces NH3
4. NH3 is oxidized to NO3-

Question 15

What is the main reservoir of nitrogen?

Answer 15

• Atmospheric N2
• Rocks and sediments (largely unavailable)

Question 16

What makes nitrogen largely biologically unavailable?

Answer 16

Most of the nitrogen is found in the atmosphere as N2
- The triple bond between the N atoms makes it unreactive

Question 17

What are the equations of the nitrogen cycle?

Answer 17

Question 18

What is anamox?

Answer 18

Anaerobic ammonium oxidation
- Oxidation of ammonia to N2
- NH4+ + NO2- –> N2 + 2 H2O
- Responsible for 30–50% of the N2 gas produced in the oceans
- Major sink for fixed nitrogen –> limits oceanic primary productivity

Question 19

What are the biotic mechanisms for fixing nitrogen?

Answer 19

• Nitrogenase-based reactions
• Low to no oxygen is essential
• Ex. Azotobacter, cyanobacteria

Question 20

What are the abiotic mechanisms for fixing nitrogen?

Answer 20

• Lightning and electrical discharges can fix N2
• Haber- Bosch process: fertilizer industry

Question 21

What is Trichodesmium?

Answer 21

Non-heterocyst forming filamentous cyanobacteria
- nifH gene analyses indicates that there are unicellular cyanobacteria that express nitrogenase too

Question 22

Biological transformations of sulfur

Question 23

What is anaerobic sulfate reduction?

Answer 23

The reduction of oxidized sulfur compunds (i.e. SO₄^2- or S⁰ to H₂)

Question 24

Where can we find purple sulfur bacteria and in what conditions?

Answer 24

• Hot springs
• Stagnant water
• Bodies of water with low oxygen concentrations

Question 25

How have humans influenced the carbon, nitrogen, and sulfur cycles?

Answer 25

Burning fossil fuels puts more carbon/nitrogen/sulfur into the environment, and they come back as things like acid rain, which can harm ecosystems