Background Information

a) Oxygen is needed to sustain all types of lives and metabolic processes in these organisms. Dissolved oxygen is important in order to indicate if water is healthy and a good quality. Air holds 95% more oxygen than water does. As the temperature decrease the amount of dissolved oxygen in water increases. Besides temperature, other abiotic factors that affect the amount of dissolved oxygen in water are wind, turbulence, and trophic state.

                The way to measure the amount of dissolved oxygen is called the Winkler method, or titration. This method is where multiple chemicals are combined into the water, such as manganous sulfate and alkaline iodine and acid. After the chemicals are combined 20 mL of the mixture is put into another bottle; here, starch indicator is put into it and sodium thiosulfate is added one drop at a time until the liquid is clear.

                The lab consisted of testing two different samples of the creek water, one at 0° and another at 20° (room temperature). Both samples were tested by the Winkler's Method. After finding the amount of thiosulfate needed to titrate the sample, the calculations used were,

mg/L Dissolved Oxygen= ml Titrant Used

(mg O₂/L x 10) x 0.698= ml O₂/L

The next experiment was to test the effects that light has on the amount of dissolved oxygen in water. The first bottle out of seven, is just left alone in the normal light of the class. The rest of the bottles should be places under a light for twenty-four hours. The second bottle should be cover in aluminum foil completely. The third bottle should have one screen taped on it, the next with two screens, three screens on the fourth bottle. On the fifth bottle there should be five screens taped on it and the sixth bottle should have eight screens on it. The final bottle should have nothing on it and left under the light as well. After the twenty-four hour period, the Winkler's Method should be done on each bottle. Then the amount of dissolved oxygen in the same should be calculated.

                From finding out the amount of dissolved oxygen is a given water source can tell whether or not the water source is healthy and can sustain life. An insufficient about of dissolved oxygen can occur in pounds and rivers, aerobatic organism, such as fish, will not be able to live there. More dissolved oxygen can support life better.