Water Pollution
Activities carried out by the human population to supply food, power, and industrial needs have a considerable effect on the environment. These effects include atmospheric and water pollution, and destroying habitats.
Water pollution is mainly caused by “run off”, containing fertilisers, enters rivers from fields. It is known as leaching when the fertilisers get washed into the river or lake. Similarly, sewage also pollutes rivers. The polluting effects of fertilisers and sewage are caused by the constituent ions such as nitrates and phosphates. They result in eutrophication.
Nitrates and phosphates enter the river and are absorbed by algae and other autotrophies. This causes them to grow rapidly at a much faster rate than usual. An algae bloom will then occur creating a blanket on the top of the water, this will block out the light and other plants on the bottom of the lake will die because they can’t carry out photosynthesis. Bacteria and other decomposers will then begin to breakdown the dead plants and any of the algae that have died. The bacteria population will now increase rapidly as the amount of organic matter increases. As the bacteria grows and performs respiration they use up oxygen in the water. The lack of oxygen will then cause any fish that are very oxygen sensitive to begin to die off. The rotting dead fish will also contribute to even lower oxygen levels, again aerobic bacteria are responsible.