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Environmental sciences Lab-2(Stream Pollution)

Free essay example:

Evs lab-2

Stream Study

Aim: To test a river at different locations to assess pollution levels.

Focused aim: To investigate pollution level of the river using bio indicators in the form of insects & dissolved oxygen.


Control variable: Number of sites

Dependant variable:Amount of insects, Level of pollution

Independent variable: Temperature, pH level, dissolved oxygen & turbidity of the stream


  • Dissolved oxygen meter
  • Digital thermometer
  • Plastic Bowl
  • Small Plastic cups
  • Net
  • Plastic box
  • pH paper


  • Each site will have different Stream Pollution Index
  • Each site will have different dissolved oxygen levels
  • Temperature & pH levels for each site will remain constant

Risk assessment:

  • Since we were studying the pollution levels of the stream & using insects as an indicator, there was an added risk that Insects might have been harmful to the human body. Hence contact with insects is not recommended.
  • Since current levels are high, any footwear in the stream such as flip-flops is not recommended.
  • Stones are wet & slippery, therefore rubber boots are recommended.


  • First each site was marked in order to start the experiment.
  • Stream was divided into 5 sites in order to analyse the stream pollution index of the stream carefully & accurately.
  • For each site(1-5), Insects were searched & caught by a Net.
  • Insects were then placed in a bowl of water in order to identify the species.
  • Turbidity of the stream was discovered.
  • pH level of the stream was discovered
  • Temperature of the stream was discovered
  • Dissolved oxygen for each site was measured using a dissolved oxygen meter
  • Insects were inputted in a table according to their Sensitivity rating, weight factor, Tolerance level & Number of Insects.
  • Stream pollution Index of the stream was then calculated.

Data collection & processing:

  • Ph of water on each site :7.6
  • Temperature: 17.1
  • Turbidity: 0
  • Site 1:1 Larva
  • Site 2:1 water strider
  • Site 3:1 water strider

              1 fish tadpole

  • Site 4:1 Larva

              1 water strider

              1 Needle bug

  • Site 5: 2 dragonfly nymph





Bug Type

Sensitivity Rating

Number of bugs found

Weight Factor

Column A    X Column C

Tolerant Bugs

Water Stider





Dragonfly Nymph





Needle Bug





Very Tolerant Bugs









Stream Pollution Index: Total of column D

                                          Total of column C                                                                                    


                                           =3.4,which is fair.

Stream Pollution index for each site:


Site 1

Site 2

Site 3

Site 4

Site 5



(Water Strider)

(Water strider)

(Larva, Water strider, water scorpion)

(Dragonfly Nymph)

Stream Pollution Index (SPI)







  Dissolved oxygen level(mg/l)

Site 1

Site 2

Site 3

Site 4

Site 5






Average Dissolved oxygen: 2.96



Based on the data above, We can observe that the stream pollution index gives a value of 3.4 which is fair,however in some sites while quality of water was just reaching a good level while in some sites quality of water was poor. Average dissolved oxygen for the stream was 2.96 which is harmful to aquatic life.


From our research & findings on this experiment we have discovered that the Stream Quality rating was fair, However dissolved oxygen is not suitable to aquatic life, obviously where dissolved oxygen is less than 3 it is harmful to aquatic life and were only seeing bugs that live on top of the water like the water strider on sites were dissolved oxygen was less than 3 and not finding other fishes at various sites. However this experiment could have been performed more accurately if :

  • By widening our time scale, for instance if we could have performed the tests at 3 different points in the day. To see whether if different dissolved oxygen levels would have been obtained & to see if there were any movement in the aquatic life.
  • By increasing the size of the nets, more aquatic life could have been captured & it could have helped us determine the stream pollution index more accurately.
  • It would be interesting to come back & run the test again to see if the levels are getting worse, and determine rate of change in the Stream pollution index & Dissolved oxygen.

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