Background Information

Pollution can be defined as “adding to the environment a potentially hazardous substance or source of energy faster than the environment can accommodate it.”

Freshwater pollution

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Organic waste, such as sewage is often dumped into rivers, as it is the easiest way to get rid of it. If the discharge of organic waste is small compared to the amount of water in the river, then it is broken down to simple in organic substances by bacteria and fungi, a process known as self-purification. If however the discharge becomes too much, bacteria thrive and begin to use up oxygen from the river, this causes a biological oxygen demand. (B.O.D)


Eutrophication means nutrient enrichment. The main factor that causes eutrophication is the heavy use of nitrogen fertilisers and the increase in discharge of phosphates from sewage works. Nitrates and phosphates are the nutrients that are usually limiting primary productivity in aquatic ecosystems. Therefore an increase in these nutrients favours an increase in rapidly growing competitive plankton species. Consumer organisms cannot increase in number as quickly in response to environmental change, this means that not all the increased primary production is eaten by the consumer organisms.

Death of the primary organisms is therefore broken down by decomposers. Breakdown to simple inorganic nutrients is an oxygen-demanding process. Dissolved oxygen levels may be reduced below those necessary for successful growth and reproduction of other species. It may also cause death of fish and other species resulting in a further oxygen demand for decomposition to take place. Thus making the situation deteriorate.

Mayfly Lymph

Scientific Name: Cloaena species

Group: Insect

Size: 10-20 mm

Position in food chain: primary consumer (herbivore)

Mayfly Nymphs are only found in very clean water containing lots of oxygen. They absorb oxygen from the water through their gills.


I think that there will be a better community structure at Debden Brook Downstream than behind the houses. i.e. a higher number of Mayfly Nymph in the river at Debden Brook Downstream compared to the location behind the houses.

This I think is true because Mayfly Nymph are found in clean water and I would assume that the water flowing behind the houses will have more pollution than Debden Brook Downstream.

Key Variables

The factors influencing the biological variable are:

* pH

* Nitrate level

* Phosphate level

* Oxygen concentration

* Speed of the flow of water

* The control will be temperature.


From the map provided of Epping forest, 2 different sites are chosen along the river. A kick sample is done at the two sites. This is used for collecting organisms in fresh running water. An open sweep or plankton net is held vertically downstream of the area being sampled by turning over stones and scraping off organisms. These are then swept into the net. Alternatively, the area being sampled is agitated by kicking and stamping so that organisms are displaced vertically and swept into the net by the current. The contents of the net is then emptied into the tray, and it is analysed for microorganisms these are then transferred carefully with a spoon into a container filled with the same river water. The type of organism is identified and recorded in a table.


* Wellingtons

* Open sweep/plankton net

* Analysing tray

* Two containers

* Plastic spoons

* 2 Bottles


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