Lesson 10

State goals for Environmental Education (per the Minnesota State Plan for Environmental Education, Greenprint, 1993)

Students will:

1. Understand ecological systems.
2. Understand the cause-and-effect relationship between human attitudes and behavior and the environment.
3. Provide experiences to assist citizens to increase their sensitivity and stewardship for the environment.
4. Understand that ecological interrelationships cross political boundaries and effects can be global.

Students will:

1. Discover the chemical parameters of a lake through testing.
2. Identify the building blocks for a healthy aquatic environment.
3. Quantify chemical testing data for future students and scientists to use.
4. Develop chemical testing skills.

Vocabulary Words

• dissolved oxygen
• chemical parameters
• pH
• anoxia
• aerobic
• anaerobic
• ecosystem
• watershed
• thermocline
• pollution
• photosynthesis
• oligotrophic

Materials

• thermometers
• Secchi disk
• calibrated line for measuring depth in meters or feet
• Hach or LaMotte dissolved oxygen test kits
• pH paper or pH meter or pH measuring device
• dock, canoe, or boat to sample from...
• clipboards, pencils, data sheets

Background

Lakes, rivers, ponds, and streams provide people with places to recreate. If we see a clear, blue lake free of algae and plants - this type of setting looks inviting. Is this a healthy environment? Looks can be deceiving and most lakes that fit this description are called oligotrophic. This means that the water has low rates of photosynthetic activity. This type of water system is limited by lack of nutrients. It can be a difficult place for amphibians, insects, and fish to live.

A lake that is teaming with plants, insects, and fish may not be as desirable for swimming, but the abundance of activity indicates a healthy, vibrant system. It is risky to try to categorize the health of an aquatic ecosystem just by looks. Testing the chemical parameters of a lake is a good starting point for ecosystem analysis.

Dissolved Oxygen

Dissolved oxygen is perhaps the most critical water quality parameter measured in a monitoring program. Dissolved oxygen concentrations will determine the kinds of chemical and biological activities that can occur in natural waters. The absence of oxygen (anoxia) can indicate severe pollution. Dissolved oxygen enters the water via photosynthesis of green plants and aeration with the atmosphere. Like all gases, oxygen is soluble inversely proportional to the temperature of the water. Warm water has a much lower capacity to hold dissolved oxygen than does cold water. Dissolved oxygen values will vary during the day due to the relationship between sunlight and photosynthesis. DO levels will peak at mid-afternoon and reach low levels just before sunrise.

Dissolved oxygen is consumed by the respiration of animals, plants, and bacteria. When water contains a heavy load of organic material, bacteria numbers increase and lower the concentration of dissolved oxygen. The amount of oxygen required for survival of different species of organisms varies considerably. Generally most game fish species need a minimum of four milligrams per liter for long term survival. Some cold water species, like trout, need more, and others, like carp and bullheads, can survive on less.

When dissolved oxygen levels fall below two milligrams per liter for extended periods of time fish-kills can occur. This often happens in shallow nutrient-rich waters. in late winter, especially if there has been a thick layer of snow covering the ice thus reducing the penetration of sunlight into the water. Sometimes the oxygen level can fall so low that anoxic conditions occur. With no dissolved oxygen present, drastic changes (anaerobic - not needing oxygen) occur in the biological activity under the water resulting in the release of hydrogen sulfide, better known as "rotten egg gas".

A strong correlation exists between population diversity (the number of different kinds of animals), population richness (the number of a particular kind of animal), and the DO content of water. Normally, clean waters with a high dissolved oxygen content support a wide diversity of aquatic life with no single species or type of organism dominating the total population. However, when dissolved oxygen levels start to fall, those organisms which need high levels of oxygen decrease in numbers, and are replaced by those that can tolerate low oxygen conditions. The diversity (different kinds) decreases and the richness (number) of pollution tolerant organisms increase. This the basis for another method of assessing water quality by biological monitoring called Benthic Macro-invertebrate Analysis and is often part of a comprehensive water quality monitoring program.

pH

The acidity, or alkalinity, of water is measured by the pH scale ranging from zero to fourteen. Water with a pH of 7 is neutral. Water with a pH of less than 7 is acidic; if it is greater than 7, alkaline. The pH scale is logarithmic, each whole number represents a ten-fold change in acidity (decreasing numbers) or alkalinity (increasing numbers). For example, water with a pH of 6 is ten times more acidic than pH 7. Water with a pH of 9 is 100 times more alkaline than pH 7.

The pH scale represents the hydrogen ion (H+) and the hydroxyl ion (OH-) concentration in water. Pure distilled water contains equal numbers of hydrogen and hydroxyl ions and is considered neutral (pH 7). If a water sample has more hydrogen than hydroxyl ions it is acidic and will have a pH of less than 7. If the water has more hydroxyl ions than hydrogen, it will be alkaline (basic) and have a pH greater than 7. Most natural waters will have pH values between 6.5-8.5. Wide variations can occur depending upon soil and other geological factors. "Pure" rain and snow will be slightly acidic (pH 5.5-5.7) because of the contact with atmospheric carbon dioxide. Acid rain (or snow) has become a major environmental concern in recent years.

Nitrogen oxides and sulfur dioxide, primarily from automobiles and coal burning power plants are converted to nitric acid and sulfuric acid in the atmosphere. This shifts the normal pH of precipitation to below pH 5.5 and can greatly impact surface water. Monitoring in northeastern Minnesota has shown the average pH of rain to be about 4.6. This level is ten times more acidic than normal. Changes in the pH of waters can have drastic results. Acid precipitation is responsible for thousands of lakes in Canada, the United States, Sweden, and Finland becoming acid to a point to where they can no longer support their normal biological diversity of organisms. At extremely high or low pH values, water becomes unsuitable for most aquatic organisms.

Activity

CAREFULLY follow the directions included in the particular test kit you use! Each brand and even even each model of a particular brand may have slightly different methods of collecting water samples and performing the particular test procedure. When you are dealing with results that measure in the "parts per million", small mistakes in procedure can be magnified in the results! Another tip is to ALWAYS take a large enough sample of water to perform TWO of each test procedure to compare results against each other. You will never be able to tell if you did the test right the first time, unless you have a second result from the same sample to compare it to!

Resources

Water Quality Testing Supplies

Acorn Naturalists
17300 E. 17th Street, J-236
Tustin CA 92680
1-800- 422- 8886

Hach Literature
1-800-227-4224
Hach Company
P.O. Box 389
Loveland CO 80539

LaMotte Chemical Products Company
P.O. Box 329
Chestertown MD 21620
1-800-344-3100
1-301-778-3100 (only in Maryland)

Carolina Biological Supply
1-800-334-5551