Measuring abiotic factors in an ecosystem

Oxygen is an abiotic factor essential for both terrestrial and aquatic organisms. Plants and animals living in the aquatic ecosystems breath the oxygen dissolved in the water and those who live on the land use oxygen present in the air. If the oxygen content comes down all of them will suffocate. You might have seen the aerator kept in the aquarium, it pumps air to dissolve oxygen into the water and keep the fishes alive. In this activity let us measure the oxygen present in an aquatic ecosystem

Experiment 1 – Dissolved Oxygen Test

1. Fill the DO bottle with collected sample water/tap or pond water without air bubbles and place the lid immediately within the water. Avoid turbulent water.
2. Open the lid carefully and add 3 – 4 drops of Manganous Sulphate.
3. Add 3 – 4 drops of Alkaline Potassium Iodide.
4. If the content of DO bottle overflows, remove the excess water by pouring in the waste collection bottle/sink carefully.
5. Shake the bottle for few seconds.
6. Allow the suspension to settle for a minute.
7. Add 8 – 10 drops of Phosphoric Acid.
8. Shake the bottle to dissolve the suspension.
9. Transfer the 8 ml of solution into a test tube.
10.  Add 1 – 2 drops of Starch (indicator).
11. Take 1ml of Sodium Thiosulphate without air bubble in the syringe.
12. Slowly add the Sodium Thiosulphate drop by drop into the solution till the solution becomes transparent. Then note the amount of Sodium Thiosulphate from the syringe. Note down the value in your data sheet.
13. Record the DO value as – DO = (volume of Sodium Thiosulphate titrated  X 20)
14. Before doing the experiment watch the video given below