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What are the two major pollutants of freshwater?
Untreated sewage and minerals from fertiliser
Why is untreated sewage water a problem?
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)
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