BioGeoChem Cycles

• Biogeochemical cycles involve the continuous movement of elements and compounds that make up nutrients through air, water, soil, rocks, and living organisms within ecosystems
• Water cycle:

  • Water is necessary for life on Earth
  • The hydrologic or water cycle collects, purifies, and distributes water supply
  • Four major processes: evaporation, condensation, precipitation, transpiration
  • Human activities alter the water cycle by withdrawing large quantities of freshwater faster than it can be replaced, clearing vegetation, and covering land with buildings and pavement
• Role of Carbon:

  • Carbon is a major building block in organisms
  • Carbon forms carbon dioxide, a component of the atmosphere acting as a storage "bank"
  • Carbon dioxide is used in photosynthesis and stored in various forms like fossil fuels and limestone shells
  • Human activities alter the carbon cycle by adding large amounts of carbon dioxide to the atmosphere through burning fossil fuels and clearing carbon-absorbing vegetation
• Role of Oxygen:

  • Oxygen is essential for life and respiration processes
  • Oxygen forms water molecules during respiration
  • Oxygen enables cells to transform energy through oxidation of food materials
• Nitrogen cycle:

  • Processes involved: Ammonification, Nitrification, Denitrification, Nitrogen Fixation
  • Human activities have doubled the annual release of nitrogen into the environment, mostly from increased use of inorganic fertilizer
  • Human input can lead to eutrophication, causing algal blooms and oxygen depletion in water ecosystems
• Phosphorus cycle:

  • Phosphorus is transferred through food webs and can be lost for long periods by washing into oceans
  • Human activities affect the phosphorus cycle by removing large amounts of phosphate for fertilizer and reducing phosphorus in soils by clearing forests
  • Phosphorus-rich run-off can lead to algae overgrowth in water bodies
• Sulfur cycle:

  • Sulfur enters the atmosphere as hydrogen sulfide and sulfur dioxide
  • Plant roots absorb sulfate ions and specialized bacteria convert them to sulfide ions
  • Human activities affect the sulfur cycle by releasing large amounts of sulfur dioxide into the atmosphere through burning coal and oil, refining petroleum, and converting metallic mineral ores
• Four major processes of the water cycle:

  • Evaporation: changes liquid water into water vapor in the atmosphere
  • Condensation: water vapor in the air cools and condenses into droplets of water forming clouds
  • Precipitation: movement of water from the atmosphere to the earth
  • Transpiration: loss of water from plants due to evaporation
• Human impact on the water cycle:

  • Withdrawal of large quantities of freshwater faster than it can be replaced
  • Clearing vegetation
  • Covering land with buildings and pavement reduces recharge of aquifers by holding water above ground
  • Increases runoff, leading to increased flooding and soil erosion
• Oxygen is one of life’s building blocks. About every fourth atom in the body of an organism is an oxygen atom.
• Oxygen serves as an acceptor of hydrogen atoms in the respiration process.
• Together with hydrogen atoms, oxygen forms water molecules during respiration
• Oxygen enables heterotrophic cells to transform energy through oxidation of food materials.
• Photosynthesis – use of CO2 along with water and the sun’s energy to produce glucose and release O2
• Respiration – both plants and animals use O2 to breakdown glucose. The by products are carbon dioxide and water.
• Decomposition – process by which organisms like bacteria break down the tissues and excretions of other organisms to simple substances. This process of decay releases carbon dioxide from the compounds retained in the bodies of organisms when they die.
• Human beings are altering the carbon cycle mostly by adding large amounts of carbon dioxide to the atmosphere when we burn carbon-containing fossil fuels and clear carbon-absorbing vegetation forests (especially tropical forests) faster than it can grow back.
• Ammonification. The process of releasing ammonia (NH3 ) from decaying protein by means of bacterial action.
• Nitrification. The action of a group of bacteria on ammonia, producing nitrates (NO3 ).
• Denitrification. This process is carried out by denitrifying or anaerobic bacteria which breaks down ammonia, nitrates, and nitrites (NO2 ), liberating free nitrogen.
• Nitrogen Fixation. This refers to the process by which bacteria in the soil or in the roots or leguminous plants converts free N2 into compounds that the plants can use
• Human beings have more than doubled the annual release of nitrogen from the land into the rest of the environment. Most of this is from the greatly increased use of inorganic fertilizer to grow crops
• Algal bloom increases the number of decomposers which use up the oxygen needed by other animals as well as other decomposers. As an effect, the water animals and the decomposers die, accumulating at the bottom of the body of water.
• Phosphorus is transferred by food webs from producers to consumers, eventually including detritus feeders and decomposers.
• Sulfur enters the atmosphere - as hydrogen sulfide, a colorless gas, highly poisonous gas with a rotten-egg smell and as sulfur dioxide, a colorless and suffocating gas.
• Sulfide ions can react with metal ions to form insoluble metallic sulfides which are deposited as rocks or metal ores and the cycle continues
• Ways of adding sulfur dioxide into the atmosphere: Burning of sulphur-containing coal and oil to produce electric power. Refining sulfur-containing petroleum to make gasoline. Conversion of sulfur-containing metallic mineral ores into free metals such as copper, lead and zinc