E5+Dissolved+Oxygen+in+Water

__Dissolved Oxygen in Water__
__The importance of dissolved oxygen in water__ Oxygen gas is slightly soluble in water and has the solubility of about 0.009dm-3. It is able to support the respiratory of plants and animals that live in water. A minimum of a level of 6ppm is required for a healthy life in the water.

__D5.1 Biological Oxygen Demand (BOD)__ BOD refers to the measure of dissolved oxygen needed or demanded for pollutants (waste form land) when decomposed in water over a period of 5 days. For water to naturally re-dissolve oxygen, the fast flow of the water will increase surface area in content with the air
 * In nature, water contains small amount of organic waste that has a BOD of up to about 1ppm, but when organic pollutants are added it can increase to 5ppm. The oxygen content of water will decrease from 9 ppm to 4ppm, and therefore aquatic life will not be able to survive in the water*

__D5.2 Distinguish between aerobic and anaerobic decomposition of organic material in water__ > Decomposition of organic matter will produce the oxides of the pollutant elements (CO2, H2O, nitrates, sulfates and phosphates) > Decomposition of organic waste will produce the hydrides of the pollutant elements (methane, ammonia and hydrogen sulfides), these are unpleasant gases and these smells characterize polluted stretches of water due to the level of oxygen being very low.
 * 1) Aerobic (using oxygen) decomposition occurs when there are lots of oxygen present in water, then organic matte r will decompose
 * 1) Anaerobic (without oxygen) decomposition occurs when there is not much oxygen left in the water, then organic waste will decompose.

__D5.3 Eutrophication__ Nitrates and Phosphates from sewage, fertilizers and detergents can act as nutrients to plant life in rivers, causing excessive growth. The additional nitrogen and phosphorus compounds encourage growth of aquatic plants often in the form of 'algal blooms' or, in coastal areas, 'red tides'. When plants die, they decompose! The bacteria that uses up oxygen which results in a decrease in the dissolved oxygen content in water..

__D5.4 Effect of heat on dissolved oxygen and metabolism in water__ Industries release hot water into river, the solubility of oxygen decreases as temperature rises. This is known as the thermal pollution!
 * The aquatic life population will decrease as it would be difficult to survive in the hotter water.
 * The metabolism of animals in the water also increases, resulting in need of more oxygen (but warmer water contains less oxygen due to low solubility)