Oxygen

❖  The air we breathe consists mostly of nitrogen, not oxygen (but we do NOT breathe nitrogen).

❖  Most of the oxygen comes from underwater organisms.

❖  Dissolved oxygen is the amount of oxygen dissolved in a body of water (river, lake, sea, etc.) It is a prerequisite for the survival of aquatic organisms.

❖  Factors that influence the levels of D.O. in a water body are:

• Temperature (D.O. levels increase as temperature decreases)
• Size (inversely proportional to the amount of D.O.)
• Water turbulence and mixing (higher turbulence means higher levels)
• Respiration and decomposition (fish breathe oxygen and microorganisms use oxygen to decompose organic matter)
• Photosynthesis (algae and plankton exist in the water and produce oxygen)

❖  The process of eutrophication has negative consequences for aquatic ecosystems.

❖  Oxygen levels decrease with increasing altitude. This affects the functions of the human body.

❖  Limiting global warming is an achievable and necessary condition for preventing low levels of oxygen in the atmosphere and improving our quality of life.