1. Cycles of the Earth & Biogeochemical Cycles Nitrogen Cycle
Slides 79-91

2. Nitrogen Cycle How does lightning help? O2 O O N N2 N N N N2 O O O2 N2
Energy breaks atmospheric nitrogen into Nitrogen oxide
Nitrogen oxide falls in rain to soil

3. Nitrogen Cycle Atmospheric nitrogen Lightning1
Denitrification by bacteria 5
Animals 7
Nitrogen fixing bacteria 1 1 1
Plants 6
Decomposers 5 2 3 4 2
Nitrification by bacteria
Nitrites
Nitrates
Ammonium 4 5 3

6. The Nitrogen Fixation Cycle: Presented by Dr. Undergrad.

7. Nitrogen Cycle (Nitrogen is required for the manufacture of amino acids and nucleic acids)
1. Reservoir – atmosphere (as N2); soil (as NH4+ or ammonium, NH3 or ammonia, N02- or nitrite, N03- or nitrate

8. Nitrogen Cycle
2. Assimilation – plants absorb nitrogen as either NH4+ or as N03-, animals obtain nitrogen by eating plants and other animals. The stages in the assimilation of nitrogen are as follows:
Nitrogen Fixation: N2 to NH4+ by nitrogen-fixing bacteria (prokaryotes in the soil and root nodules), N2 to N03- by lightning and UV radiation.
Nitrification: NH4+ to N02- and N02- to N03- by various nitrifying bacteria.

9. Nitrogen Cycle
3. Release – Denitrifying bacteria convert N03- back to N2 (denitrification); detrivorous bacteria convert organic compounds back to NH4+ (ammonification); animals excrete NH4+ (or NH3) urea, or uric acid.

10. Nitrogen Cycle
1. Reservoir – atmosphere (as N2); soil (as NH4+ or ammonium, NH3 or ammonia, N02- or nitrite, N03- or nitrate
2. Assimilation – plants absorb nitrogen as either NH4+ or as N03-, animals obtain nitrogen by eating plants and other animals.
3. Release – Denitrifying bacteria convert N03- back to N2; detrivorous bacteria convert organic compounds back to NH4+ ; animals excrete NH4+, urea, or uric acid.

11. Effects of Human Activities on the Nitrogen Cycle
We alter the nitrogen cycle by:
Adding gases that contribute to acid rain.
Adding nitrous oxide to the atmosphere through farming practices which can warm the atmosphere and deplete ozone.
Contaminating ground water from nitrate ions in inorganic fertilizers.
Releasing nitrogen into the troposphere through deforestation.

12. Effects of Human Activities on the Nitrogen Cycle
Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined.
Figure 3-30

13. Nitrogen Cycle

14. Nitrogen Removal Basics