does polluted water have more or less dissolved oxygen then unpolluted water? why ?
Water pollution is not directly connected to oxygenation levels. However, certain types of pollution can result in low oxygen levels and thus dissolved oxygen level can be an indication of how polluted the water is. Generally, a higher dissolved oxygen level indicates better water quality. For example, phosphate runoff leads to excessive growth of algae which then leads to excessive amounts of decaying algae which depletes the water of oxygen. Low dissolved oxygen levels may also be found in areas where organic material (dead plant and animal matter) is decaying. Bacteria require oxygen to decompose organic waste, thus, deplete the water of oxygen. Areas near sewage discharges sometimes have low dissolved oxygen levels due to this effect. Yet, many types of water pollution have no effect on the amount of oxygen dissolved in the water.