For the last usage of the data logger, it was used to measure the amount of dissolved oxygen content in water. Firstly, we connected the connecting cable from MultiLog’s input I/O-1 to the D02 adaptor. Then connect D02 probe to the Oxygen Adaptor (0 to 25% 02 0 to 125% Sat). We referred to the instruction sheet that comes together with the oxygen adaptor to assemble the probe and filled it with electrolyte. Then we switched it on and make sure the MultLog displays “Ready”. We click PORT until “INPUT -1” is displayed. Click SENSOR until “Oxygen D02” is displayed. Click RANGE until “0 ÷ 125%” is displayed. Click RATE until “Every SEC” is displayed. Click SAMPLES until “Samples = 2000” is displayed. Click TRIGGER until “Not Active” is displayed. Click the run/stop and wait for the reading to stabilize. Finally, we took the reading (in %) and click the run/stop button to stop.
To test for the turbidity of the water, we took a beaker to collect the water from the river and then we used a disc which was painted white and black and put it beneath the beaker to see if it was clear. If the black and white disc could be seen from the top view, the water is clear. Thus, since we could clearly see the disc from above, and when we placed the beaker of water under the strong sunlight, very little particles were seen floating in the water. Thus, we can conclude that the turbidity of the water is clear. We also put the water under strong sunlight to check if there were any small particles, which can be seen, suspended in the water.
Finally, for the last test for the velocity of the water, we used a ping-pong ball and stick it to a one-metre raffia string. We placed it on the surface of the water gently and allowed the flow of the water to carry it. When the raffia string becomes taut, we stopped the stopwatch and record the timing taken for the ping-pong ball to travel one metre. Though, this experiment failed for the Pasar Ris group, as the water does not seems to flow at all and the ping-pong ball did not move. We tried the second time and a breeze blew causing the ping-pong ball to move together in the direction of the breeze. We tried the third and last time and a speedboat sped past, causing the ping-pong ball to travel yet together with it.
Figure 1. Table of water qualities in Kallang River
For the riverbank, fine particles could be seen suspending in the water due to the dust from the train and vehicles. Vehicles by the road side especially lorries produce exhaust fumes. There are small particles and dust contained in the fumes and when they were blown by wind, the particles tend to enter the river water. Thus, fine particles were suspended in the water by the riverbank. Due to the construction site and the speedboats in the centre of the river, these causes tiny black particles to enter the river water. For the bottom of the centre of the river, most of the particles in the water tend to float up to the surface and thus, the water at the bottom of the centre of the river is clean and have little visible particles. If the particles did not float up, most probably it will sink under the sand and the sand would weigh it down.
Because of the exhaust fumes from the vehicles and litters left by the visitors at the riverbank, it causes the water by the riverbank to turn a little acidic. Due to the wastewater discharged by the speedboat and the construction site, it provides alkalinity to the river water at the surface of the water at the center. The river water at the bottom of the center of the river is slightly alkaline, as the waste from the construction site might have sunk down and mixed with the river water, causing the alkalinity. It is not as alkaline as the surface as the waste particles tend to float and seldom sink.
The amount of dissolved oxygen in the water at the riverbank is much more than the rest of the places is due to the fact that the water is shallow and more oxygen can dissolve into it easily. The surface has much more amount of dissolved oxygen than the bottom of the center of the river is because the oxygen dissolved first into the surface and then the oxygen molecules will slowly mix with the bottom.
The clarity of the water at the riverbank is much better than the one in the center is due to the speed of the water traveling. The faster it travels, the clearer the water. The dirty particles in the water tend to obstruct the smooth flowing of the water and when the particles clog together, the water will be unclear.
Figure 2. Table of water qualities in Pasir Ris River
The water at the river mouth has fine particles suspended in the water. There are even dead fishes seen floating in the river water. The fine particles might be due to the littering by visitors or the oil spill by the speedboat. However, only small particles were seen in the water at the upper stream of the river. The small particles might be due to the minor construction site situated at the source of the river.
The acidity of the river water at the mouth might be due to the littering and the oil spill from the speedboat too. Thus, the acidity of the river is quite high. As for the alkalinity in the water at the upper stream, the water is very alkaline as it might be due to the construction site at an even upper stream. The wastewater discharged at the construction site flowed down and mixed with the water and thus, the alkalinity.
There were more dissolved oxygen at the river mouth because it is more open aired compared to the upper stream and lesser organisms which uses the dissolved oxygen. The lesser amount of dissolved oxygen was because of the fact that there were more organisms living at the upper stream and the organisms used a lot of the dissolved oxygen to survive.
There was not much movement of the water in fact. The river water moved due to the breeze blowing and the speedboat traveling. When we left the ping-pong ball at the surface of the water, it did not move and only moved slightly at a speed of 5m/h when the breeze blew. Thus, we were unable to carry out the experiment for the velocity of the river.
Overall, I think that the this experiment is quite well-done except for the fact that the velocity of the river water at Pasar Ris could not be carried out because of the stagnancy of the water and the continuous blowing of breeze and speedboats whizzing past. As for the Kallang River, the velocity of the water might be also due to the wind or other factors. Thus, I think that the experiment for the velocity of the river has failed. And the pH value of the rivers might be due to other factors such as acidity of the rain, which causes it to be acidic or alkaline. The turbidity of the river can be further improved by taking the river water samples and then test it for even microorganisms. We should have used a microscope and observed the microorganisms and then evaporate the river water to see if there are more micro organisms in the water so we can be sure if the water is really clear.
Christabel Cho Jia Yu
04IP05 04
