1. How Matter and Nutrients Cycle
Biogeochemical Cycle - recycle nutrients through the earth’s air, land water, and living organisms
Complete path moves through four major components (reservoirs)
Atmosphere
Hydrosphere
Lithosphere
Biosphere

2. Biogeochemical Cycles
3 types
Hydrologic (water) – water moves through spheres, most found in hydropshere
Atmospheric – large portion of a given element exists in gaseous form (nitrogen, carbon)
Sedimentary – most found in lithosphere, generally very slow (phosphorus,sulfur)

3. The Nitrogen Cycle

4. What happens to atmospheric nitrogen in the nitrogen cycle?
Atmospheric Nitrogen (N2) N N
Bacteria
(cyanobacteria in soil and water or rhizobium bacteria on the roots of plants)
Lightning
Nitrogen Fixation
Nitrates (NO3)
Nitrogen combines with Oxygen to make Nitrates
Ammonia (NH3)
Nitrogen combines with Hydrogen to make Ammonia

5. Nitrogen Fixation N2 + 3H2 → NH3 → (dissolves) → NH4+
the process that causes the strong two-atom nitrogen molecules found in the atmosphere to break apart so they can combine with other atoms.
Nitrogen gets “fixed” when it is combined with oxygen or hydrogen.
N2 + 3H2 → NH3 → (dissolves) → NH4+
(ammonia) (ammonium)

6. But……
Very few plants can use NH3 (ammonia) or NH4+ (ammonium)
Nitrification can help

7. Nitrification NH4+→NO2-→NO3-
Nitrifying bacteria in the ground first combine ammonia or ammonium with oxygen to form nitrites. Then another group of nitrifying bacteria convert nitrites to nitrates which green plants can absorb and use!
NH4+→NO2-→NO3-
[nitrite (toxic)] [nitrate (nutrient)]

8. How do plants and animals get the nitrogen they need?
Assimilation

9. Assimilation
Roots: absorb NH3, NH4+, NO3- to make DNA, amino acids, proteins
Animals: eat plants or plant-eating animals to make DNA, amino acids, proteins

10. How does the nitrogen return to the atmosphere?
2 more steps!
Ammonification
Denitrification

11. Ammonification Decaying organisms→NH3 → NH4+ What happens to the NH4+?
Bacteria and fungi decomposers break down amino acids from dead animals and wastes into ammonium
Decaying organisms→NH3 → NH4+
dissolves
What happens to the NH4+?

12. Denitrification NH3 → NO2- → N2 and N2O (nitrous oxide) Atmosphere
Denitrifying bacteria live deep in soil and in aquatic sediments where conditions make it difficult for them to get oxygen. The denitrifying bacteria use nitrates as an alternative to oxygen, leaving free nitrogen gas as a byproduct. They close the nitrogen cycle!
NH3 → NO2- → N2 and N2O (nitrous oxide)
NH NO3-
Atmosphere
Soil

13. How are humans affecting the nitrogen cycle?
Use of nitrogen-rich fertilizers
can cause eutrophication
Burning fossil fuels and forests
Releases solid forms of nitrogen
Farming
Livestock wastes release
nitrogen into soil and water