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Extended Experimental Investigation | Bulimba Creek


Home | Introduction | Aim & Hypothesis | Materials | Method | Results | Discussion | Conclusion | Bibliography | Appendix

Bacteria cultures

1. Prepare cultures by setting agar gel in Petri dishes.
2. To grow a bacteria culture, the utmost hygiene must be observed. Peel back the plastic on a cotton swab, so that when held, the cotton tip is well free of the hand.
3. Dip the cotton tip into the water sample and swirl to obtain an even sample of the contents of the jar. Tap off any excess water on the cotton tip.
4. Holding the Petri dish by the fingertips and making sure not to touch the agar, swipe the cotton tip from side to side over the agar. Rotate the dish ninety degrees and repeat to obtain even coverage. Make two separate cultures for each water sample: one to grow at room temperature and one to incubate at 35oC.
5. Replace the cover of the Petri dish and seal with adhesive tape. Label each dish with the location the water sample was taken from as well as an identification number e.g. 1 for cultures at room temperature and 2 for incubated cultures.
6. Leave half of the dishes in a stable environment at room temperature and incubate the other half at 35oC for at least 24 hours.
7. Remove dishes from the incubator. Remove the adhesive tape on the Petri dishes and observe bacterial growth on the agar. E. Coli colonies will show as a dull green growth, which may also be iridescent. Observe the colonies under a microscope at low power (4x) to determine structure and to compare to other colonies.

Ammonia nitrates:

1. Fill a blank test tube with distilled water. This is the reference tube. Fill a second test tube to the 5mL mark with the water to be tested.
2. Add a packet of Ammonium Salicylate to the sample tube. Cap and shake until the powder is dissolved. Leave to stand for 3 minutes.
3. Open and add a packet of Ammonium Cyanurate to the sample tube. Cap and shake until dissolved. Water should take on a lime green to green hue depending on concentration of ammonia in the water.
4. Leave for 15 minutes for colour to develop fully.
5. Place the Ammonia colorimetric disc into the viewer. Place the blank tube into the left slot and the sample tube in the right slot. Rotate the disc to match the colour to the colour of the water. Take the reading from the disc in g/L.


1. Reset thermometer by flicking the tube downwards to force the mercury into the bulb.
2. Place the bulb of the thermometer into the creek, making sure that it does not rest on the creek bed. Hold for two minutes, or until the mercury ceases its movement.
3. Take the reading from the temperature from the mark that the meniscus rests at.

Conductivity and pH

1. Wash the detector of the electronic meter thoroughly with tap or distilled water. Set the meter to read pH.

2. Place the base of the meter in the water and hold until the reading is constant.

3. Take the reading displayed on the meter.

4. Press 'mode' until the reading for conductivity is displayed in mS (milliseimens). Take the reading displayed on the meter.

Dissolved oxygen

1. Clean the glass jar and glass square jar with clean water. Take the glass jar with stopper and completely submerge in the creek. Allow all air bubbles to escape, and stopper the jar underwater.
2. Take the stopper off and add a packet of Dissolved Oxygen 1 and a packet of Dissolved Oxygen 2 to the water. Stopper the jar again, taking care not to trap any air bubbles. If any air bubbles are trapped, discard the test and start again.
3. Shake the jar until the powder is dissolved. Leave jar undisturbed and allow for floc to fall to half the volume of the jar.
4. When the floc has fallen to the half way mark on the jar, shake again. Allow to rest and for the floc to fall to the half way line again.
5. Take the stopper off and add the contents of Dissolved Oxygen 3. Stopper the jar, taking care not to trap any air bubbles. If any air bubbles are trapped, discard test and start again.
6. Shake jar to dissolve the floc. Solution will turn a golden yellow colour in the presence of oxygen. Allow to rest for 8 minutes to allow the colour to develop fully.
7. Take the stopper off the jar and pour 23mL of solution into the small glass square jar.
8. Use sodium thiosulfate for the titration. For every drop of sodium thiosulfate added to the solution, swirl the jar to mix thoroughly. Record the number of drops required to reach the end point, in which the solution becomes colourless.
9. To obtain the concentration of dissolved oxygen in the sample, the concentration in g/L is equal to the number of drops of sodium thiosulfate required to reach the end point. To obtain the low-range concentration of dissolved oxygen, multiply this figure by 0.2.

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