Dissolved oxygen in water is very important for aquatic life. What processes are responsible for the reduction of dissolved oxygen in water?
The processes which are responsible for the reduction of dissolved oxygen in water are excessive use of phosphatic and nitrate fertilisers, detergents, the discharge of human sewage and organic waste from food, paper and pulp industries. The microorganisms which oxidise organic matter also used oxygen dissolved in water. Moreover, during night, photosynthesis stops but the aquatic plants continue to respire, resulting in reduction of dissolved oxygen.