Includes current lectures and notes of Prof. Signor Rinno D. Montales

15th January 2012


Biogeochemical Cycle

As energy and matter flow through an ecosystem, matter must be recycled and reused. Substances such as water, carbon, nitrogen, sulphur and phosphorus each pass between the living and non living words through biogeochemical cycles.

The energy from the sub causes water to move into the atmosphere. This is called evaporation. Water moving from the atmosphere to the earth is called precipitation.

In the carbon-oxygen cycle there are two basic life processes involved – respiration and photosynthesis.

  1. During cellular respiration, glucose is oxidized and carbon dioxide is released.
  2. During photosynthesis, green plants use the carbon dioxide and energy from the sun to make oxygen, glucose and water.

When plants and animals die, the organic compounds of their bodies are broken down by microorganisms. One of the end products that eventually form is carbon dioxide.

In spite of the abundance of nitrogen in the atmosphere, plants cannot change the element nitrogen into compounds they need. The nitrogen must be in the form of nitrate. Synbiotic bacteria can change atmospheric nitrogen into ammonium compound

Bacteria of decay break down the protein of dead organisms to ammonia or ammonium compounds. Some bacteria cause nitrogen to return to the atmosphere by breaking down ammonia in the soil.

Phosphorus is present in the soil in the form of phosphate. Through weathering, phosphate rocks contribute to the amount of phosphate in the soil. Phosphate is taken in by plants and passed on to the food chain when plants and animals die. The bacteria converts the dead bodies into phosphates and return them into the soil. Guano deposits are also sources of phosphate.

Sulfur and phosphorus cycles are both lithosphoric cycles. Sulfur comes from several sources – volcanoes, the action of soil microorganisms – combustion of fossil fuels such as oil, gas, and coal. When fuel is burned, oxygen combines to form oxides. When oxides reach the atmosphere, they combine with rain and form sulphuric acid, which in turn falls to the ground as acid precipitation.