1. Biogeochemical Cycles
(Water, Carbon, Nitrogen, Phosphorus, Sulfur)

2. What is a biogeochemical cycle?
A biogeochemical cycle is the continual recycling of nutrients through the air, water, rock, soil, and living organisms.
All of these nutrients are essential to life.
No new molecules are created – what we have is what was here at the beginning.

3. The Water Cycle

5. The Water Cycle
Groundwater is water that sinks into the soil and is stored in aquifers.
An aquifer is a groundwater storage area.

6. Humans alter the water cycle by…
Withdrawing large quantities of freshwater for agriculture leading to groundwater depletion.
Clearing vegetation for agriculture, roads, building, and mining.
Covering land with buildings and concrete which increases runoff, and prevents water from becoming ground water.
Altering the quality of the water by the addition of nutrients from chemicals and pollutants.

7. The Carbon Cycle

9. Humans alter the carbon cycle by…
Clearing trees therefore, the trees cannot remove the carbon dioxide from the air
Burn fossil fuels which release a large amount of carbon into the air

10. The Phosphorous Cycle

12. Humans alter the phosphorus cycle by…
Mining for phosphate rock to make inorganic fertilizers
Cutting down tropical trees reduces the amount of phosphorus in the tropical soil
Runoff from animal wastes, fertilizers, and sewage add phosphorus to aquatic systems

13. The Sulfur Cycle

14. Acidic fog and precipitation
Water
Air Pollutant
Acidic fog and precipitation
Sulfur trioxide
Sulfuric acid
Ammonia
Ammonium sulfate
Oxygen
Sulfur dioxide
Hydrogen sulfide
Plants
Volcano
Dimethyl sulfide
Industries
Animals
Combustion of Fossil Fuels
Ocean
Sulfate salts
Decaying matter
Metallic
sulfide deposits
Sulfur
Hydrogen sulfide
Industry, burning fossil fuels add sulfur to atmosphere

15. Humans alter the sulfur cycle by…
Burning coal and oil to create electricity which releases sulfur into the air
Refining petroleum to create gasoline
Creating metals from ores

16. The Nitrogen Cycle

18. The Nitrogen Cycle
Nitrogen in the air is in the form of N2 which is unusable to plants and animals. The N2 needs to be converted to a useable form – this is done by 1) lightening and 2) bacteria in the water and soil.
Nitrogen fixation – bacteria in the soil convert N2 to NH3 so that plants can use it
Nitrification – bacteria take the NH3 and turn it into nitrite (NO2 - toxic) and nitrate (NO3) ions
Assimilation – Plants absorb the ammonia and nitrate; animals get nitrogen by eating plants
Ammonification – decomposer bacteria take animal and plant wastes and turn it into ammonia
Denitrification – ammonia is converted into nitrites and nitrates and then to N2 where it is released into the air

19. The Nitrogen Cycle
Plants need nitrogen in the form of nitrates to make nucleic acids (DNA) and amino acids.

20. Humans alter the nitrogen cycle by…
Burning fuel releases nitric oxide (NO) which converts to (HNO3) in the atmosphere and falls back to the earth as acid rain
Using inorganic fertilizers which releases N2O (nitrous oxide) into the atmosphere which depletes the ozone layer
Destroy forests, grasslands, and wetlands which releases the N in the soil and the plants
Agricultural runoff and sewage goes into waterways and the nitrates disrupt the aquatic ecosystems
When working with crops (irrigating, harvest, burn to create room for) nitrogen is taken from the topsoil.