Oxygen and Nitrogen Cycles

Question 1

Explain the O2 Cycle

Answer 1

Refer to L13 slides 5-7 for a visual representation

NATURAL OXYGEN CYCLE

1) Plants take in energy from the sun, H2O and CO2 to do photosynthesis yea wtv

2) plants release O2 (dissolves in the atmosphere) and organic compounds. these both contribute to respiration

3)respiration creates CO2 and H2O (goes back to plants)

SIMPLIFIED O2 CYCLE (everything in natural O2 cycle but with this stuff too. Everything not included in Natural O2 cycle are affected by human activity):

4) O2 and organic compounds also contribute to combustion, which creates CO2 and H2O (goes back to plants)

5a) O2 contributes to Nitrification (creating NO3 from O2 and NH3) This happens naturally (lightning) or from human activity (fossil fuel combustion)

5b) leads to denitrification (creating N2). The N2 then contributes to creating H2O (goes back to plants). Happens at wastewater treatment plants

6a) O2 contributes to sulfur oxidation (creating SO4 from S and O2. can be formed through bacteriological oxidation (acid mine drainage, sewer corrosion) or fossil duel combustion

6b) and sulfate reduction (creating H2S). This then contributes to creating H2O (goes back to plants)

Question 2

What is special about photosynthesis in the O2 cycle?

Answer 2

it’s the only natural process that forms oxygen from water in large enough quantities to matter ecologically

Question 3

Explain Respiration

Answer 3

Athe biochemical oxidation of chemical compounds to produce energy needed for activity, growth, and reproduction

Question 4

Explain Combustion

Answer 4

a small part of the natural cycle (forest fires, grass fires), but increasing due to fossil fuel combustion

Question 5

What are some sources of Nitrogen?

Answer 5

• direct addition through fertilizers (N-based fertilizers, manures, soil organic matters)
• biological N fixation from atmosphere –> a process to convert N2 from atmosphere into format that plants can absorb through roots

Question 6

What are some pathways for Nitrogen Loss?

Answer 6

Denitrification: conversion of NO3 to N gass = lost to atm

Volatilization: conversion of NH4 to NH3

Plant uptake: assimilation of inorganic forms of H (NH4 and NO3)

Leaching loss of nitrate from water draining through soil profiles

Runoff: loss of nitrate as water flows on the ground surface

Question 7

Key points of the Nitrogen Cycle

Answer 7

• N is essential plant nutrient
  -N is one of most deficient plant nutrients (that’s why N fertilizers exist)
• N availability in soils affected by mineralization and immobilization
• most plant available N from decomp of organic matter:

Mineralization/Ammonification: conversion of organic N to ammonium by soil microbes ( organic N -> ammonia -> ammonium)

Nitrification: conversation of ammonium to nitrate by nitrifying bacteria (ammonium -> nitrite -> nitrate)

Question 8

Environmental Impacts and Mitigation Approaches

Answer 8

Impacts:
- reduced light/penetration availability
- depleted dissolved oxygen (hypoxia/dead zone)
- decreased biodiversity in aquatic systems

Mitigation:
regulating nutrient sources
- phytoremediation: uses plants to clean up contaminated environments
- improving wastewater treatment