Solubility of Gases in water
Most gases which are important for biological processes dissolve readily and specially in water. The solubility of any gas in water generally varies between zero and a theoretical maximum saturation level. The latter represents the amount of gas that dissolves in water when the atmosphere and water are in equilibrium with one another. The oxygen readily dissolves in waters. The amount of dissolved oxygen varies with depth in a water body. Dissolved oxygen is needed by living organisms for respiration and also for the decomposition of dead organic matter in a water body. Aquatic vegetation and phytoplankton require carbon dioxide for photosynthesis. The carbon dioxide in aquatic environment is contributed by respiration of aquatic organism and decomposition. Carbon dioxide can directly dise from the atmosphere into the water and it readily dissolves to form carbonic acid (H2CO3) which effects the pH of the water. It is also present in fresh water as carbonates and bicarbonates of calcium, magnesium and other minerals. Nitrogen, hydrogen, sulphur dioxide and ammonia are some of the other gases which dissolve in water readily.