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APES Lab

Testing Water Quality

Purpose: To test surface water for water quality. Tests will be for pH, dissolved oxygen, carbon dioxide, alkalinity, hardness, nitrates/nitrites and phosphates. To analyze the data obtained to assess the overall quality of the body of water.

Materials: Hach or LaMotte water test kits pH meter

Procedure: Obtain a container of water.

Record the following information about the sample:

Date: __________________ Location:____________________

General description of the source of your water: ____________________________________ ___________________________________________________________________________

Tests:

1. pH Test

pH measurements are made on water because this is a good indication of whether the body of water might be contaminated – especially if the pH is above or below the normal ranged. Many aquatic life forms are very sensitive to acid levels in the water. Pollution tends to make water more acidic. Most bodies of water have the highest diversity when the pH is close to 7.

Results: ph_________________

Interpretation:

1. What effect would this pH have on living organisms in the water?

2. What effect would this pH have on plants in the water?

3. What are some factors that could cause this particular body of water to have its pH?

4. What is an acceptable pH range for most aquatic life?

2. Alkalinity

Alkalinity is a measure of all the substances in water which have the ability to react with the acids in water and buffer the pH. (A buffer has the power to keep the pH from changing.) Pure water has a pH of 7 and has zero alkalinity. Alkalinity is important for aquatic life because it protects or “buffers” much as a Tums or Alka Seltzer does in your stomach. It keeps the pH from changing and makes the water less affected by factors such as acid rain or acid spills. The main sources of alkalinity in water are rocks (such as limestone) which contain carbonates or bicarbonates, and respiration. Water with a total alkalinity of 100-120 ppm is considered to bed the best waters for fish and aquatic organisms. Lakes with total alkalinity of 200 ppm are quite high. Alkalinity can be increased in water by adding line to it. Alkalinity is considered a fairly reliable measure of the productivity of a body of water.

Results: Alkalinity _____________________ (units are ppm of CaCO3)

Interpretation:

1. Is this body considered to have a high productivity or not?

2. Why would alkalinity of rainwater increase as it runs through the soil?

3. Considering the location of the site from which this water sample was taken, what might be the source of the alkalinity?

3. Carbon dioxide

As green plants carry on photosynthesis only in the presence of sunlight, they as well as the animals in the water carry on respiration at night. Therefore, more CO2 tends to build up in water during the night rather than in the daytime. If the CO2 levels are high and dissolved oxygen levels are low, fish have trouble carrying on respiration. The problem increases if the water temperature rises. Fortunately for fish, “free” (uncombined) CO2 rarely exceeds 20 ppm and most fish can survive this amount with no ill effects. Levels greater than this for any length of time can be lethal.

Results ________________ ppm

Interpretation

Using your knowledge about the origin of this water sample write a sentence or two which summarizes your findings.

4. Hardness

Hardness in water is the amount of Ca and Mg in the water. The natural source of hardness is usually Limestone rock. The most frequent test performed on water is for Total Harness. Hardness is important to living organisms because soft water makes heavy metals such as Hg and Pb more poisonous to fish. Some nonmetals such as ammonia and certain acids are also more toxic to fish in soft water. Vertebrates need Ca to build bones. All living things need Ca and Mg in order for proper cell functions. Chlorophyll contains Mg. Drinking water with a total harness of 250 ppm is best. >500 ppm can make you very ill.

Results ________________________ ppm

Interpretation

Use information from the background section and your knowledge concerning the origin of your water sample and write a sentence or two which summarizes your

findings.

5. Nitrates/Nitrite

Nitrogen compounds are essential for healthy plant growth. Nitrogen is a major constituent of commercial fertilizer. The presence of excessive amounts of nitrogen compounds in water supplies presents a major pollution problem. Large amounts of nitrates and nitrites in water are harmful to humans. Nitrates in conjunction with phosphates can cause algal blooms that lead to cultural eutrophication. The EPA states that 10 ppm of nitrate/nitrogen is a limit that should not be exceeded. Lower amounts are desirable.

Results __________________ ppm

Interpretation

Using your knowledge of the nitrogen cycle, the origin of the water sample and the test results, write a sentence or two which summarizes your findings including what you think might be the source of the nitrates in this particular body of water.

6. Phosphate

Phosphate in water along with the presence of Nitrates stimulate the growth of algae. This in turn can lead to accelerated eutrophication of a body of water. The concentration of phosphates in water is normally not more that 0.1 ppm unless the water has been polluted.

Results _____________________ ppm

Interpretation

Use information from your readings and your knowledge of the location of the water sample site to summarize your finding.

7. Dissolved Oxygen (DO)

Dissolved oxygen is one of the best indicators of general water quality. As a general rule, the higher the DO, the better the quality of the water. Dissolved oxygen is dependent on temperature as warm liquids hold less dissolved oxygen than cold liquids. When organic wastes decompose in a body of water, dissolved oxygen is used up. Because more aquatic organisms are “cold blooded,” their metabolism rises as temperature goes up and the amount of available oxygen goes down. This often results in fish kills, especially if the DO drops below 5 ppm.

Results ___________________ ppm or mg/L

Interpretation

Using information that you obtained with your test kit and the background section, write a few sentences about the quality of your water sample.

8. Coliform Bacteria

Another excellent indicator of water quality is based on the number of coliform bacteria. Coliform bacteria normally life in the intestines of mammals and are excreted with fecal wastes. Some forms are pathogenic but even if they are not, if they are present in a water sample this indicates that they sample has been through an animal intestine. (This is called an indicator organism.) The EPA does not allow any coliform bacteria in drinking water. It does, however, allow 200 colonies/100 mL in water used for swimming.

Results Positive Negative for coliform bacteria

__________________________ colonies/100 mL

Interpretation

1. Would your water sample be suitable for drinking? Why or why not?

2. Would your water sample be suitable for swimming? Why or why not?

3. If your water sample contains coliform bacteria, what might be the source?

Results Table:

Final Analysis Questions:

1. How do you rate the overall quality of the water you tested? Justify your answer using your test result.

2. How is the body of water that you tested used at the present time?

3. After analyzing the data which you collected, do you think this is an oligotrophic or eutrophic body of water? Explain your answer

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