Dissolved oxygen is essential for the survival of fish. In this activity you will determine if it was the amount of dissolved gasses in water that killed the fish.

DO, 4 ppm, unsaturated, saturated and supersaturated solutions, percent concentration, average monthly data vs. daily data

Data has been collected during the month of August. Graph this and then answer several questions.

In graphing this data, choose scales on the axis of the graphs to use as much of the paper as possible.

Title the graph Daily Dissolved Oxygen Levels

Label the x-axis as the days of the month and the y-axis as DO concentration (ppm).

On the y axis - pick a scale that will show the largest changes in DO levels. Connect these points starting from day 1.

Data Analysis Of Graph

1. What does the graph show? Is it a consistent level of DO?

2. What days fell below the minimum DO levels needed for fish survival?

3. What days show the highest and lowest levels of DO?

4. Explain why the average monthly DO levels cannot show sharp increases in DO on particular days?

Percent Saturation

Just as there is a minimum level of DO, there is also a maximum level of DO for many fish. In many cases, too much DO at a particular water temperature can kill fish.

Table 9 on page 53 shows how much DO is needed for a particular water temperature to have a 100% oxygen saturation.

125% > - too high for many species to survive

124% - excellent for most fish

79% - satisfactory for most fish

59% < - most species die

 

Read and study

The DO concentrations needed for saturated water solutions at various temperatures are provided in Table 9. Use this table to decide whether the DO is below, at, or above the saturation level for each measurement in the August Data table. You'll also need the following formula:

Percent of saturation = ppm DO measured x 100%

ppm DO for saturation

For example, on day one measurement, the water temperature was 20° C and the dissolved oxygen concentration was 9.1 ppm. According to Table 9, 9.2 ppm dissolved oxygen is a saturated solution at 20° C.

Percent of saturation = (9.1 ppm / 9.2 ppm) x 100% = 98.9%

So, on day one, the saturation level of dissolved oxygen was 98.9%; slightly unsaturated.

1. Pick six days from the August Data (use your graph to determine which days may have the highest or lowest percent saturation) to calculate percent saturation.

2. Do any of these days fall below or above the acceptable percent saturation levels?

3. Based on your data analysis - what appears to have killed the fish? Support your answer with data.

During the next lab activity we will check for DO levels of water and determine how to make a supersaturated solution.

In the electronic journals, students are to enter: KLW

Know- what we already knew about DO and fish requirements

Learned - what we learned about DO and how it can affect life

Want To Learn - formulate a question about unsaturated, saturated and supersaturated levels of DO which can be tested during the lab activity

August Daily Temperature And Dissolved Oxygen Levels
 

Teacher version of activity

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Joseph F. Zisk
jzisk@sciteched.org
©1998