1. Biogeochemical Cycles
Review

2. The Water Cycle (Hydrologic Cycle)

3. 3 important needs for water
Photosynthesis
Respiration
Digestion
Major Reservoir
Oceans (97%), Ice Caps

4. The Water Cycle
Water is released from the surface through evaporation.
Evapotranspiration is the loss of H2O from the leaves of plants as they exchange gases.
Once in the atmosphere, water molecules undergo condensation.
This gives us precipitation which sends the H2O back to the Earth.
Precipitation: Rain, snow, sleet, hail

5. The Water Cycle
Precipitation infiltrates the soil and percolates down into the deeper layers of the soil or it will become runoff.
Percolated H2O may become part of the groundwater, which flows underground to the ocean.
Aquifer: water saturated rock/soil
Percolated water may also be used by plants for photosynthesis.

6. Human Intervention in the Hydrologic Cycle
Ground & surface water depletion.
Ground & surface water pollution.
Deforestation, particularly in temperate and tropical forests, which interferes with the cycle by decreasing transpiration and increasing runoff/flooding

7. The Carbon Cycle

8. The Carbon Cycle CO2 makes up ~0.035% of the atmosphere
Used by plants during photosynthesis to make carbohydrates (sugar)
Carbs are then used during cellular respiration, which is a process that gives off CO2 into the atmosphere

9. The Carbon Cycle
Decomposers degrade the remains of plants & animals and return the CO2 to the atmosphere as well.

10. The Carbon Cycle Sinks:
Most of the C on earth is in the form of limestone, a type of sedimentary rock.
In the ocean, C is found dissolved as carbonate and bicarbonate ions.
Old growth forests because they store large amounts of carbon in the biomass.
Limestone contains ~80% CaCO3

11. The Carbon Cycle Exists in abiotic environment as:
CO2
Carbonate rocks
Fossil fuel
Dead organic matter
Enters biotic environment through:
Photosynthesis
Returns to atmosphere by:
Respiration
Decomposition
Burning/Combustion

12. The Carbon Cycle How does C get into the Ocean?
Carbon dioxide dissolves/diffuse into water. Combines with calcium in water to form CaCO3 (calcium carbonate)
Large amounts of CaCO3 deposits are found on the ocean floor
Come from the remains or organisms such as mollusks and coral
Shells decay and turn into limestone, limestone dissolves in water and releases carbon back into atmosphere

13. Human Intervention in the Carbon Cycle
Since the Industrial Revolution we have dramatically increased CO2 in our atmosphere due to:
Deforestation: decreases the plants available for photosynthesis, thus decreasing the uptake of CO2
Forests burning and releasing the carbon in the “carbon sink”
Increased combustion of fossil fuels
Increased CO2 in the atmosphere has exacerbated global climate change by holding in infrared heat around earth that would normally escape into space.

14. The Nitrogen Cycle

16. The Nitrogen Cycle Atmosphere is 78% N
Essential to life because it is used to form amino acids (proteins), nucleic acids (DNA/RNA), and ATP (cell energy)
Plants and animals are unable to use N2 it must be “fixed” to a usable form
Ammonia or Nitrates
By Bacteria or Lightning

17. The Nitrogen Cycle The N cycle has 5 main steps:
N fixation is the conversion of atmospheric N2 into ammonia (NH3)
The bacteria, Rhizobium, are able to fix N
Rhizobium is found in the root nodules of legumes
Peas, beans, clover, alfalfa
Some plants use ammonia, but more can use nitrates
Nitrification
Other bacteria convert ammonia into Nitrites NO2- which is not usable by plants. Therefore, different bacteria must convert NO2- into nitrates (NO3-) that plants can use.

19. The Nitrogen Cycle
Assimilation is when plant roots absorb ammonia, ammonium ions, or nitrates and make the substance they require for life.
Ammonification takes place when dead N rich organisms, their parts, or their metabolic wastes are converted to ammonia and ammonium ions by decomposing bacteria. Soil is major reservior
Denitrification is the process of nitrate ions being converted back to gas & released into the atmosphere.

21. Human Intervention in the N Cycle
NO is released when fossil fuels are combusted. NO in the atmosphere forms nitric acid, which results in acid deposition and smog formation.
N2O gas is a greenhouse gas and is derived from livestock waste and used as a fertilizer.
N is removed from an ecosystem if plants are removed.
N, when added to aquatic ecosystems from agricultural runoff and municipal waste treatment, induces eutrophication, an enrichment of the ecosystem resulting in algal blooms.

22. Eutrophication/Cultural Eutrophication
Caused by excess
Nitrogen
Phosphorus

23. Phosphorus Cycle

24. Phosphorus Cycle
Important b/c it makes up cell membranes, part of nucleic acids, and ATP
Very slow cycle because there is no atmospheric/gas stage.
Major reservoir: Rocks
Phosphorous is in rocks and P ions do not dissolve very well in water.
Most is insoluble and found on the ocean floor as a phosphorus sink.

25. Phosphorus Cycle
Rock containing P must be weathered to release the minerals or removed via mining.
P is taken up by producers and transferred to consumers.
Waste and Decay of organisms releases P

26. Phosphorus Cycle
Leaching: water dissolves phosphates in rocks and carries to lake, stream, etc
Dissolved phosphate: used by plants and passed through food chain
Animals return phosphorus to environment by
Excretion of Waste
Death/Decay

27. Human Intervention in the Phosphorus Cycle
Phosphate mines that form large pits & result in runoff pollution
Removing vegetation lowers phosphorus availability in an ecosystem
Similar to increases in N, increases in P leads to eutrophication in aquatic ecosystems.
P is found in sewage

28. Sulfur Cycle

29. Sulfur Cycle
Most S is found in rocks as iron disulfide (pyrite) or mineral salts like calcium sulfate (gypsum).
Sulfur is released by weathering, volcanic activity & hydrothermal vents.
S is take up by producers and passed to consumers and released again after decomposition.

30. Human Intervention in the Sulfur Cycle
Fossil fuel combustion releases sulfur dioxide, which forms sulfuric acid in the atmosphere and results in acid deposition
Refining of petroleum and smelting releases sulfur compounds
Coal mining results in sulfur release, causing damage to aquatic ecosystems
Large amounts of sulfur dioxide and sulfate aerosols cool the atmosphere because they prevent the penetration of UV radiation