Materials

Thermometer Data Collection Student Worksheet (optional)

Background Information
It is important to know the temperature of the water at the test site because it could help predict and/or confirm other conditions of the water. For example, the water temperature has a direct influence on other water quality factors such as dissolved oxygen (DO), biological oxygen demand (BOD), as well as on the survival of some aquatic species.

The metabolic rates of aquatic organisms increases in warm water. Since metabolism requires oxygen, some species may not survive if there is not enough oxygen in the water to meet their needs. Also, water temperature may affect the reproductive rates of some aquatic species; some species may not be able to reproduce in warmer waters. Since bacteria and other disease causing organisms grow faster in warm water, the susceptibility of aquatic organisms to disease in warm water increases as well.

Sudden increases in temperature may be a result of thermal pollution which is the discharge of large amounts of warm water from industrial plants. Sudden changes in water temperature may cause thermal shock in some aquatic species and result in the death of that species. Thermal pollution, even if gradual, may disrupt the ecosystem balance in such a way to eliminate heat intolerant species from that area.

Test Procedure

Measure the water temperature at the same level that the sample for the dissolved oxygen test is taken if possible. That way, a correlation may be made between DO level and temperature (especially if you do more than one test).   Make sure the tip of the thermometer is at least a few inches below the surface of the water and take a reading when the temperature has stabilized (usually after a couple of minutes).   Record the temperature in degrees Celsius (ºC). If the temperature is measured in degrees Fahrenheit (ºF), use a unit conversion calculator to convert to Celsius.

What to Expect
In general, when the water temperature is colder, the amount of dissolved oxygen (DO) should be higher and therefore the water will be able to support aquatic life (fish and plants) more readily. This is because oxygen can dissolve in colder water more easily than in warmer water. The opposite can be expected in warmer waters.

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