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Lab 10 - Experiment 1: Environmental Variables that Effect DO

 

Levels

 

In this experiment, you will observe environmental conditions that effect the levels of dissolved

 

oxygen present in a water sample. You will use a LaMotte Dissolved Oxygen TesTabs? to

 

obtain qualitative data on the levels present in water samples.

 

Materials:

 

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(5) 8 ml Test tubes

 

26 Dissolved Oxygen TesTabs?

 

1 Canning jar

 

Aluminum foil

 

1 Packet of salt

 

100 ml Beaker

 

Parafilm?

 

1 Pair of gloves

 

Permanent Marker

 

Graph paper

 

Test tube rack

 

Thermometer

 

*Timer

 

*Printed, color copy of this procedure

 

*2 Water samples

 

*Boiling water

 

*Tap Water

 

*You must provide

 

 

General Procedure?Analyzing Dissolved Oxygen

 

1.

 

2.

 

3.

 

4.

 

 

Add four LaMotte Dissolved Oxygen TesTabs? to the 8 ml test tube.

 

Seal with Parafilm? immediately, making sure there are no air bubbles in the sample.

 

Mix by inverting until the tablets have disintegrated (5-8 minutes).

 

Wait five minutes.

 

 

?

 

 

5. Compare the color of the sample to the color chart below. Record as ppm DO in Table 1.

 

 

Effects of Biochemical Oxygen Demand

 

Field Trip - Water Collection

 

1. Identify a water location which you believe features abundant micro-organismic, plant or

 

animal life.

 

2. Use graph paper to sketch a diagram of where you will collect your water sample. Be

 

sure to label the graph with descriptive information, and indicate any other critical

 

information that might affect the water quality. For example:

 

? Has it recently flooded?

 

? Is the area experiencing a drought?

 

? Is there snow or ice present?

 

? What is the temperature?

 

? Is the surrounding animal/marine life steady/predictable?

 

? What kind of animals/plants are local to the area?

 

This diagram is called a Field Report and will become useful should you need to reassess the original environment.

 

3. Label two test tubes with the body of water?s name and the collection date.

 

4. Go into ?the field? to obtain your water samples. To do this:

 

? Pack up your test tubes, gloves, aluminum foil, test tube rack, 4 LaMotte

 

Dissolved Oxygen TesTabs?, a printed copy of this procedure, a timer, and

 

Parafilm?.

 

? Go to the first water sample location.

 

NOTE: Some collectors may wish to wade into the water to obtain their water

 

sample. As a general rule of thumb, water collectors should NOT wade into

 

flowing water if the water depth (in feet) x the water velocity (in feet per second)

 

is greater than or equal to 10. If you have any hesitations regarding water-safety,

 

do NOT enter the water!

 

? Completely submerge one of the test tubes under water.

 

 

?

 

 

? Seal immediately with Parafilm?.

 

? Cover this tube with aluminum foil, and place it in your test tube rack on a flat

 

surface (if possible). Upon return, this test tube should be stored in a dark

 

location at room temperature for five days.

 

? Repeat Step C for the second test tube, and immediately test the DO according

 

to the procedure listed at the beginning of this experiment (located under the title

 

?General Procedure - Analyzing Dissolved Oxygen?). Record your data in Table 1.

 

? Do not return the contents from test tube B to the water as this will contaminate

 

the water source. Take both of the test tubes back to your ?lab?, place the first

 

test tube according to Step e, and discard of the second test tubes contents in a

 

sink.

 

2. After 5 days have passed, repeat the ?General Procedure - Analyzing Dissolved

 

Oxygen? on the first test tube. Record your data in Table 1

 

Note: The difference in the DO levels between the uncovered tube (the second test

 

tube) and the covered tube (the first test tube ) is the biochemical oxygen demand of the

 

water sample.

 

Effects of Temperature

 

1. Boil water vigorously for 10 minutes.

 

2. Place a canning jar in the sink and fill with boiling water until overflowing and then cap.

 

Do not test yet, wait 24 hours.

 

3. Fill two test tubes with tap water until they are overflowing. Seal immediately with

 

Parafilm?.

 

4. Place one test tube in the refrigerator and leave one at room temperature.

 

5. Make sure there is no air space between the top of the test tube and the Parafilm?

 

seal. Let the tubes sit over night.

 

6. The next day, open the jar from Step 7 immediately and test according to the procedure

 

above, but use six Test Tab? tablets instead of four.

 

7. Test the DO levels of the room temperature test tube sample, as well as the refrigerated

 

test tube sample, with four tablets as normal.

 

8. After the color change has occurred, take the temperature of each sample and record

 

the results in Table 1.

 

Effects of Salinity

 

1. In a 100 ml beaker, add one packet of salt to 50 ml water.

 

2. Use this solution to fill a test tube labeled ?brine? until the tube is overflowing. Test the

 

DO according to the protocol.

 

 

Table 1:Dissolved Oxygen (ppm)

 

 

?

 

 

Sample

 

Fresh sample

 

Sample after 5 days

 

Biochemical Oxygen Demand

 

Effect of Temperature

 

RT (temperature: ____)

 

Cold (temperature: ____)

 

Boiled (temperature:_____)

 

Effect of Salinity

 

Brine solution

 

 

?

 

 

ppm

 

 

Positive Response

 

 

Positive Response

 

 

Questions:

 

1. Research the Winkler Method for testing dissolved oxygen. Write the protocol for this

 

testing method and a brief explanation of the reactions that take place within the test.

 

Also, what are some of the factors that could lead to potential error using this test?

 

 

2. State your conclusions on the level of oxygen in the samples you analyzed. What types

 

of water systems would you expect them to come from? Are these values high or low?

 

What type of aquatic life would you expect to find in the sources of these samples?

 

 

3. Cold, dense water sinks at the poles and drives a deep circulation in the North Atlantic

 

Ocean. What would you expect the comparative DO levels to be in this water? Why?

 

 

4. Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen required for

 

aquatic, aerobic biological organisms to break-down organic matter over a period of

 

time(assuming that temperature and other environmental factors are held at a constant

 

value). BOD can be used to indicate the organic quality of a given water sample. If a

 

water sample is undiluted, BOD can be determined with the equation: Initial DO - Final

 

DO = BOD. If you measure an initial DO of 2.5, and measure a final DO of 1.2 after 5

 

days have passed, what is the BOD?

 

 

?

 

 



 

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