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ENVI 4 biogeochemical cycles FINAL


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ENVI 4 biogeochemical cycles FINAL

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ENVI 4 biogeochemical cycles FINAL

  1. 1. Biogeochemical Cycles Chapter 4
  2. 2. The Hydrologic (Water) Cycle  Evaporation: When the heat of the sun causes water to turn to water vapor, it is known as evaporation.  Condensation: As the water vapor moves higher in the atmosphere, it cools down due to a decrease in the temperature. On cooling, the water vapor condenses to form tiny droplets of water.  Precipitation: The tiny droplets of water that are formed as a result of condensation keep on accumulating in the clouds. When a cloud can no longer accommodate any more water droplets, the water is released from them in the form of rain, hail, sleet, or snow.
  3. 3. The Hydrologic (Water) Cycle  Run-Off: The water that falls back to the surface of the earth either stays on the surface of the earth, or flows off the surface into water bodies like rivers, lakes and reservoirs. This flow is termed as run- off.  Transpiration: Plants absorb water from the soil and transport it to the leaves via the stem. When this water evaporates from the leaves and stem, it is termed as transpiration.  Infiltration: When the water on the surface of the earth seeps down the ground, it is called percolation or infiltration. It later forms aquifers in low-lying regions.
  4. 4. The Carbon-Oxygen Cycle  Carbon enters the atmosphere as carbon dioxide from respiration (breathing) and combustion (burning).  Carbon dioxide is absorbed by producers (life forms that make their own food e.g. plants) to make carbohydrates in photosynthesis . These producers then put off oxygen.  Animals feed on the plants. Thus passing the carbon compounds along the food chain. Most of the carbon these animals consume however is exhaled as carbon dioxide. This is through the process of respiration. The animals and plants then eventually die.
  5. 5. The Carbon-Oxygen Cycle  The dead organisms (dead animals and plants) are eaten by decomposers in the ground. The carbon that was in their bodies is then returned to the atmosphere as carbon dioxide.  In some circumstances the process of decomposition is prevented. The decomposed plants and animals may then be available as fossil fuel in the future for combustion.
  6. 6. The Nitrogen Cycle  Two ways nitrogen gas can be fixed: through lightning and a special type of bacteria called nitrogen fixing bacteria (rhizobium) take in atmospheric nitrogen and produce ammonia (NH3), a process called ammonification.  Other bacteria use this ammonia to produce nitrates and nitrites, which are nitrogen and oxygen containing compounds.  Plants are consumed by other organisms which use the plant amino acids to make their own.  Decomposers convert the nitrogen found in other organisms into ammonia and return it to the soil. A few of these type of bacteria return nitrogen to the atmosphere by a process called denitrification, however this amount is small.
  7. 7. The Phosphorus Cycle  The phosphorus enters the soil and water through the weathering of rocks.  Plants take in these phosphorus ions from the soil.  The phosphates are then transferred from plants to herbivores animals.  These herbivores animals are eaten by carnivores.  The phosphates that are absorbed by the animals are returned to the soil through excretion and from decomposition of plants and dead material by microbes.
  8. 8. The Phosphorus Cycle  The dead plant materials and other waste products are decayed through the action of bacteria.  The phosphate is released out to the environment by this process.  The phosphate in the soil is leached out or eroded into water.  The water is again utilized by algae and plants as nutrients.
  9. 9. Human Impacts to Phosphorus Cycle  Human impacts on the phosphorus cycle are from the introduction of synthetic fertilizers.  Plants may not be able to use the phosphate in the form of fertilizers; most of the nutrients is lost through water run-off.  The phosphate present in the water sediments at bottom of water body.  In certain large feed application, it may result in excessive run- off of phosphate into streams.  The phosphate from the sewage is not removed, if it is not treated and extra amount of phosphate enters the water body.  High concentration of phosphate in water system can lead to eutrophication of fresh and inshore marine waters, which leads to algal blooms.
  10. 10. The Sulfur Cycle  The process begins with the weathering of rocks, which releases stored sulfur.  Sulfur comes into contact with the air, converting it into sulfates.  Sulfate is taken up by plants and microorganisms and is changed to organic form.  Sulfur moves up to food chain.  When organisms die, some sulfur is released back to sulfate and enter microorganisms.
  11. 11. The Sulfur Cycle  Natural sources, such as volcanoes, emit sulfur into the air.  Sulfur eventually settles back to the earth, or comes through rainfall, with some also going to the ocean.  Sulfur is also drained to rivers and lakes, eventually to the oceans.  Some of the sulfur from the oceans go back to the atmosphere through the sea spray.  Remaining sulfur go to the ocean floor and form ferrous sulfide, which is responsible for the black color of most marine sediments.
  12. 12. The Sulfur Cycle