Water pollution + (triple) effects of deforestation

What are the two major pollutants of freshwater?

Untreated sewage and minerals from fertiliser

Why is untreated sewage water a problem?

- Aerobic bacteria in the water polluted by sewage use up the dissolved oxygen in the water as they break down organic materials. This reduction in the level of oxygen kills larger animals such as freshwater insects and fish. Basically only organisms that can survive are the ones who can live in low oxygen conditions like anaerobic bacteria

- This reduces biodiversity in aquatic ecosystem

- Untreated sewage contains pathogenic bacteria, which are a danger to human health

Why is sewage treatment needed?

Remove solid and suspended organic matter and pathogenic microorganisms, so that cleaner waste can be discharged into waterways.

How can the level of pollution by organic material be monitored?

By the presence or abscence of indicator species

What is eutrophication?

Excessive nutrients (these are the inorganic mineral ions like phosphates and nitrates) in a water body causing overgrowth of algae (algae bloom)

What are the two main sources of excess minerals for eutrophication?

Untreated or treated sewage

Artificial nitrate or phosphate fertilisers.

Explain the consequences of fertiliser containing nitrates polluting a river (6)

- Leads to eutrophication

- Fertilisers contain nitrates which are very soluble/dissolve in water so they are leached into bodies of water (like lakes) because of rainwater

- Nitrates result in the rapid overgrowth of algae (algae bloom)

- They block light so plants underneath die/less photosynthesis

- Less oxygen released

- These dead plants are broken down by decomposers like bacteria and fungi who respire aerobically and use up dissolved oxygen, reducing O2 levels even more

- The water contains too little oxygen so fish and other aerobic animals die

What happens to th water in severe cases?

It becomes anoxic (containing very little oxygen) and smelly from gases like hydrogen sulfide and methane from bacteria. By this stage only anaerobic bacteria can survive

As more plants die, the numbers of decomposers increase = more respiration = less oxygen

The nitrates stimulate growth of all plants in the river or lake, but algae grow especially quickly leading to algal bloom. Fish can't eat quickly enough