1. Nutrient Cycles

2. Nitrogen cycle Phosphorus Carbon Oxygen Water
Life on the earth depends on the flow of energy (wavy arrows) from the sun through the biosphere and back into space, the cycling of crucial elements (solid arrows around ovals).
Nitrogen
cycle
Biosphere
Heat
Phosphorus
Carbon
Oxygen
Water
Figure 3.7
Natural capital: life on the earth depends on the flow of energy (wavy arrows) from the sun through the biosphere and back into space, the cycling of crucial elements (solid arrows around ovals), and gravity, which keeps atmospheric gases from escaping into space and helps recycle nutrients through air, water, soil, and organisms. This simplified model depicts only a few of the many cycling elements.
Heat in the environment 2

3. WATER CYCLE

4. WATER CYCLE Evaporation: liquid water becomes vapor (gas) in air
Transpiration: loss of water by plant through leaves
Evaporation & transpiration RETURN water to atmosphere
Condensation: water is changed from a vapor to a liquid
Responsible for cloud formation
Precipitation: water released from clouds in the form of rain, freezing rain, sleet, snow, or hail
Returns water to earth

5. Effects of Deforestation on the WATER CYCLE
Forests acts as an enormous reservoir of water, which attracts humidity and creates rain clouds.
With deforestation, this hydraulic regulation is destroyed and reduces the absorption capacity.
Rain continues to fall, floods the ground (b/c it is not absorbed by trees) and sediment runs off into streams and rivers

6. CARBON CYCLE Main carbon sinks (storage): Oceans and forests
Major processes include: Photosynthesis, Respiration, Decomposition (biological) and Combustion
Photosynthesis is the major source of O2 in the atmosphere!

7. Effects of Human Activities on Carbon Cycle
We alter the carbon cycle by adding excess CO2 to the atmosphere through:
Burning fossil fuels.
Clearing vegetation faster than it is replaced.
Burning fossil fuels increases CO2 in the air; decrease use of fossil fuels to decrease the amount of CO2 in the air 7

8. Nitrogen Cycle
Nitrogen is the MOST abundant gas in the atmosphere

9. Abiotic Nitrogen Fixation
Conversion of atmospheric nitrogen (N2) into ammonia (NH3) and nitrate (NO3-)
(NO3-) results from lightning and cosmic radiation ~ 10% of all nitrogen fixation
3. Multistep process:
a.) N2 + 2O2 → 2 NO2
b.) 3 NO2 + H2O → HNO3- + NO
c.) 2 NO + O2 → 2 NO2

10. Biological Nitrogen Fixation
Nodule
~ 2-3 cm long
Accomplished by soil bacteria (many are aerobic)
Symbiotic fixation: Rhizobium (found in roots of legumes; provides direct source of NH3 to plants)
EX: of legumes: peas, alfalfa, soybeans, clover, peanuts
Cyanobacteria fix nitrogen in aquatic environments
Clover root

11. Nitrification
Ammonia is oxidized into nitrite, then to nitrate by 2 different species of bacteria
1.) 2 NH3 + 3 O2 → 2 NO H2O + 2 H+ (Nitrosomonas)
2.) 2 NO O2 → 2 NO3- (Nitrobacter)
2nd Step
1st Step

12. Assimilation
Plant roots absorb nitrates for use in making molecules such as DNA, amino acids and proteins.
Consumers eat producers and receive nitrogen containing compounds (proteins, DNA, etc)

13. Ammonification
1. After nitrogen has served its purpose in living organisms, decomposing bacteria convert the nitrogen-rich compounds, wastes, and dead bodies into simpler compounds such as NH 3
2. Decomposition rates affect the level of nutrients available

14. Denitrification
1. Nitrate ions and nitrite ions are converted into nitrous oxide gas and nitrogen gas.
2. This happens when a soil nutrient is reduced and released into the atmosphere as a gas.

15. Effects of Human Activities on the Nitrogen Cycle
Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined. 15

16. Effects of Human Activities on 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. 16

17. Phosphorous Cycle

18. Effects of Human Activities on the Phosphorous Cycle
We remove large amounts of phosphate from the earth to make fertilizer.
We reduce phosphorous in tropical soils by clearing forests.
We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers. 18

19. Phosphorus
1. Bacteria are not as important in the phosphorus cycle as in the nitrogen cycle.
2. Phosphorus is not usually found in the atmosphere or in a gas state only as dust.
3. The phosphorus cycle is slow and phosphorus is usually found in rock formations and ocean sediments.
4. Phosphorus is found in fertilizers because most soil is deficient in it and plants need it.
5. Phosphorus is usually insoluble in water and is not found in most aquatic environments.

20. The Sulfur Cycle 20

21. Effects of Human Activities on the Sulfur Cycle
1. We add sulfur dioxide to the atmosphere by:
Burning coal and oil
Refining sulfur containing petroleum.
Convert sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment.
2. Adding sulfur to the atmosphere contributes to acid rain 21

22. Law of Conservation of Matter
Matter cannot be created or destroyed in an isolated system; it cycles
Biogeochemical cycles demonstrate the Law of Conservation of Matter
Nitrogen
cycle
Biosphere
Heat
Phosphorus
Carbon
Oxygen
Water