Materials and Resources

MWRA Handout

Note: This text is made available courtesy of the Massachusetts Water Resources Authority. We have scanned in the original manual pages and converted the files to text. Unfortunately, the pictures were lost and there are some irregularities in the formatting. Our apologies for the inconvenience.

TEST I: Temperature

Brief Summary

Water and air temperatures are measured with a shielded Celsius thermometer.

Note: To obtain the most accurate results, this test should be completed in the field.

Background

Most aquatic organisms have evolved to take advantage of one of water's most unique features: its heat capacity, or its unusual ability to absorb thermal energy (heat) with only minimal changes in temperature. Most fish, amphibians and sea mammals require fairly constant water temperature, and can only survive within certain temperature ranges. They can handle seasonal fluctuations because water temperatures change much more slowly than air temperatures. If water temperatures change more than 1C to 2C (2 to 4F) within 24 hours, aquatic animals can suffer thermal shock, which can injure or kill them, and it can also make fish more susceptible to disease and parasites. In addition, the stages of these creatures' life cycles are highly sensitive to seasonal changes in water temperature. Changing temperatures signal many animals to mate, lay eggs or migrate.

Unfortunately, many of the side effects of our industrial society affect water temperature, usually raising it. These increases in water temperature often have a negative effect on water quality.

Natural Factors That Influence Water Temperature

• The size (volume) of the body of water: large bodies change temperature more slowly, so a small stream. or pond will vary in temperature more than a large lake or ocean.

• The depth of the water: deep waters are cooler because they warm up more slowly; the deeper the water, the less sunlight warms it and the cooler it stays.

• The color and turbidity of the water - dark waters convert more sunlight to heat.

• The temperature of tributary water: rivers or lakes receiving water from snow-fed mountain streams will stay cooler than those fed by streams meandering through flatlands.

• The amount of overhanging vegetation: during the summer, shaded water will stay cooler than water exposed to sunlight.

• The direction of a stream: streams that run south are exposed to more sun than those running east/west.

• The latitude, season, and time of day.

Human Factors That Influence Water Temperature

• Industrial facilities and power plants discharge water used for cooling

• Storm runoff contains water warmed by urban surfaces, such as streets, sidewalks, and parking lots.

• Cutting trees along banks exposes water to more sunlight.

• Soil erosion increases the amount of suspended solids, making water turbid, and turbid water absorbs more heat from the sun.

Effects of Raising Water Temperature

• Warmer water holds less oxygen, yet produces conditions that require more oxygen.

• The rate of photosynthesis by algae and larger aquatic plants increases. The result of this increase is a higher level of BOD because of the increased amount of decaying organic material.

• The metabolic rates of aquatic organisms increase. As their metabolism increases, they become more active and consume more oxygen, reducing the DO level.

• Organisms become more sensitive to toxic chemicals, parasites and diseases.

• Bacteria (including pathogenic bacteria) and parasites can sometimes grow.

Testing for Temperature

Overview:	In this test, you will first measure the air temperature. Then you will either measure the temperature of the water at the same location and depth from which the water samples are taken for the other tests., or you will examine variations in water temperature in a body of water. You may hold the thermometer directly in the body of water itself or in a container of sample water. If you test water from a container, you should measure its temperature before the water has time to warm up or cool down.
Length of Test:	5-10 minutes (including waiting time)
Difficulty of Test:	Simple
Protective Clothing:	Rubber gloves
Suggestion:	Always predict the water temperature before taking it. You may be surprised fairly often.

PROCEDURE

1. Measure the air temperature by holding the thermometer in the shade for about two minutes. Do not let the thermometer rest on surfaces that might transmit their own heat.

2. Record the air temperature on the Data Recording Form.

3. Measure the water temperature by submerging the thermometer into the body of water (or a container of sample water) and holding it there for two minutes. The thermometer should be at least four inches beneath the surface and should not touch the bottom. If possible, try to hold it at the same depth from which you drew the samples for the other tests. Note: If you are working from a bridge, you should measure the temperature of sample water from a container. Regardless of how fast you pull up the thermometer, air temperature and evaporative cooling will distort your measurement.

4. Record the water temperature on the Data Recording Form.

5. Wash off the thermometer with tap water and wipe it dry before returning to the kit.

Interpreting Results

What factors at the site might contribute to the water's temperature:

• size, depth, and flow of the water?
• turbidity and color?
• shade and vegetation?
• direction of stream?
• season, time of day and recent weather?

Did you find any indications of thermal pollution (activities that raise the water temperature above its natural level) such as industrial discharges, storm drain discharges, or discharges from electrical generating plants? These influences can raise water temperature in the ocean as well as in freshwater bodies.

Water temperature affects several other water quality factors:

• Dissolved oxygen levels are higher in colder water.

• Higher temperatures speed up chemical reactions in plants and animals. Fish increase their metabolic rate in warm water and need more oxygen.

• Some fish can only live in certain temperature ranges, for example:
  • Native brook trout live where water remains below 13C (55F) in the summer;
  • Rainbow trout and salmon need water temperatures of 13 - 20C (55 - 68F) in the summer;
  • Carp and catfish prefer water above 20C (68F) in the summer;

• Plant life changes with water temperature:
  • Green algae bloom above 25C (77F) and blue-green algae bloom at 30C (86'F). (Algae blooms occur when water has too many nutrients, and they lead to low oxygen levels.)
  • Many fresh water aquatic plants thrive at 20C (68F), while fewer plants live below 13C (55F).

Extension Activities

1. If you locate a site where two streams converge or if you find an outflow from an industrial site or a utility plant, take the water temperature from as many locations as you can and plot or draw the thermal plume. (See illustration.) Similarly, if you locate an area where runoff from paved areas enters a stream, take the water temperature upstream and downstream of this runoff, and measure the temperature of the runoff itself.

2. Bring a jar of water from your sampling site back to the classroom. Heat and cool different samples of the water to different temperatures. Perform the pH test, DO test, and salinity test to see if temperature affects the results.

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