Water Quality (GMHDRNC)

Summary:

Learn how to manage pH and oxygen levels to maintain the proper habitat for fish species.

Grade Level:

7 - 12

Recommended Setting:

Indoor or outdoor classroom, preferably aquatic setting

Outdoor Activity:

No

Location:

Governor Mike Huckabee Delta Rivers Nature Center, Pine Bluff

Contact:

Education Program Coordinator, 870-534-0011

Duration:

45 minutes - 1 hour

Suggested Number of Participants:

10 - 25

Special Conditions:

Water activity

Objectives:

  • Learn how to perform water quality tests.
  • Understand how temperature, acidity and oxygen levels are vital to fish survival.

Key Terms*:

Acid

Base

pH scale

*See glossary for definations

Materials:

Dissolved oxygen tests

pH tests

Water sampling materials

Background:

The quality of water in which fish live is vital to their survival. Water testing gives biologists and conservationists insight into the elements that affect fish populations. Fish need adequate oxygen, a pH level above 5.0 and consistent temperature. Good quality water will support more species and greater fish populations than polluted or stagnant water.

Procedure:

  1. If necessary, water samples can be collected before the program.
  2. Discuss the three main factors that determine water quality: oxygen, temperature and acidity.
    • While respiration is different for humans and fish, the key ingredient is the same: oxygen. Oxygen is added to water in two ways. First, in flowing water, oxygen is taken from the surrounding air as the water tumbles over rocks and trees in shallow areas. Second, the main source of oxygen is through plants. During photosynthesis, aquatic plants such as plankton and duckweed filter harmful carbon dioxide and replace it with oxygen as they convert sunlight into energy. However, plants also use oxygen to decompose, decreasing levels. Pollution of any kind also removes oxygen from the water.
    • Water temperature may be the single best indicator of where fish will be and how they will behave. Each species requires a specific temperature for survival. Trout, for example, are only in colder bodies of water. Bass may be the most indifferent and live in a wide range of temperatures. Temperature affects the amount of oxygen water can hold. Since molecules within the water are more active with higher temperatures, hot water cannot hold as much oxygen. Adversely, fish require more oxygen in warmer water. When the water becomes too warm, fish migrate to deeper water where the temperature is more moderate.
    • Acidity in liquids is measured using a 0-14 scale called the pH scale. Distilled water has a pH of 7 and is considered neutral. Levels below 7 are considered acidic. Lemon juice, which contains citric acid, has a pH of 2. Levels above 7 are considered basic or alkaline. Ammonia, a chemical in many cleaning agents, is a base with a pH of 11. Acidity in bodies of water is linked to many factors. Carbon dioxide and water in the air give rain (even without pollution) a pH between 5 and 6. In the Ouachita Mountains of Arkansas, soil contains a higher concentration of sandstone, which leads to slightly more acidic water. Limestone in the soil, on the other hand, tends to neutralize some acids. If the water becomes too acidic, creatures in the water begin to die off. Bass and catfish cannot survive in water with a pH below 5. Fish eggs are susceptible to acid as well, so as the pH lowers, so does the egg fertility and fewer fish hatch and grow to adulthood. Insect larvae are also dependent on good water quality for survival. They are food for smaller fish that then are food for larger fish, so they are vital to the food chain.
  3. Take participants to an aquatic setting such as the catfish pond at Delta Rivers Nature Center or a stream near their school and collect water samples.
  4. Return to the classroom and run tests for pH and dissolved oxygen.
  5. Allow time for questions, and if possible, examine the water under a microscope to talk about healthy microinvertebrate levels.

Review:

  • Why is temperature important to fish survival?
  • Why are lakes sometimes naturally slightly acidic?
  • Why would a scientist look at a water sample under the microscope?

Glossary:

Acid – a compound that tastes sour and can neutralize alkalis and redden blue litmus paper; has a pH value of less than seven

 

Base – in chemistry, a compound that reacts with an acid to form a salt, having a pH of more than seven

 

pH scale – measure of a liquid’s or solid’s alkalinity, represented on a scale of 0 to 14 with 7 being a neutral state, 0 the most acidic and 14 the most alkaline