4.16 understand the biological consequences of pollution of water by sewage

Water pollution by sewage:

- Sewage is rich in minerals and nutrients to allow organisms like decomposers to reproduce, increasing their population. This causes depletion of oxygen as decomposers will respire aerobically, so oxygen levels will decrease for other organisms. Aquatic animals can die as a result.
- Sewage is rich in phosphates which promote the growth of algae. Formation of algae can block sunlight, which prevents plants from absorbing sunlight via photosynthesis, resulting in the death of aquatic plants.
- Sewage contains bacteria respiring aerobically, which uses up oxygen levels in the water.