LIMNOLOGY TESTS
NAME____________________________
PARTNER____________________________
PARTNER____________________________
Background:
Water isn’t simply water. The water that we know is always water and something else. It’s the
combination that we have to work with that makes it useful and interesting. Water picks up
more of the materials that it contacts than anything else and it is changed more by what it
takes up than most of the materials in our environment. Water is the “universal solvent”.
In the hydrologic cycle, when water vapor in the atmosphere condenses to form droplets of
liquid water, it takes in some of the other vapors of the atmosphere. If the droplets freeze, it
likely did so around fine dust from salts, smoke, industry waste, soil, etc. The droplets will
contain some oxygen gas, nitrogen gas and carbon dioxide. There may even be traces of
ozone, nitrous oxides, argon and other gases.
Healthy habitats generally have greater biodiversity. Most habitats have indicator species that
help determine the health of an environment. Biodiversity includes plants, bacteria and protists
as well as animals.
In this lab, you will observe and test various characteristics to determine the quality of water in
the simulated river tank or a stagnant tank. Each team of students will conduct each test at
least one time. This data will be averaged and used as a compared to standards. Each team
of students will select one of the limnology tests, formulate a question, hypothesis and design
an experiment. The questions must involve at least one of the following limnology tests: pH,
turbidity, silica, nitrates, phosphates, total hardness (calcium & magnesium), dissolved oxygen
and carbon dioxide, salinity. Additionally, a limited biodiversity test and fecal coliform test will
be conducted at another time.
Make a data table with headings for each water quality test. Read the information provided for
each test. Prepare an oral and written presentation to explain your specific test(s) and its
significance. This presentation will include your question tested, hypothesis, background
research, procedures, data, effects of high/low measurements on other chemicals, plants
and animals and causes of high/low concentrations. All data should be analyzed. This
analysis might include averages, ranges, percent changes and/or other statistical data. The
conclusion should either support or reject the hypothesis with justification. When appropriate
relate your tests to photosynthesis, food webs/chains and the transfer of energy within a food
chain, soil, climate, and/or pollution. Most of the tests performed should also be related to one
or more biogeochemical cycles. Also, the conclusion should state sources of error and how
those sources most likely affected the data. Finally, cite your sources (bibliography). Some
information is provided on the following pages, while other parts of your report will need to be
researched in the textbook, internet and other available resources.
You may separate the contents of your presentation in logical subtopics among your partners,
however, all partners must be well-versed in ALL aspects of your experiment. The
presentations may be on posters or powerpoint. All members of your team must contribute to
research, experimental design, presentation preparation, oral presentation and fielding
questions following the presentation.
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LIMNOLOGY TESTS
NOTE: The chemical tests contain hazardous materials. Lab safety rules must be followed.
Even if you are not conducting a test, others may be, so do not roam around room, conduct
any unauthorized tests or participate in any behaviors that could be construed as horseplay.
Follow the safety precautions printed for your specific test(s). Read the MSDS sheets before
opening any bottles. Use safety goggles and aprons as appropriate.
After cleaning your work area, wash your hands before leaving class each day.
NOVA computers with probes may be available for some tests.
Make note of the room temperature each day. Unless you heat or cool the water or store it in
direct sunlight, the water and room temperature may be assumed to be nearly equal.
FYI: Parts per million (ppm) is nearly the same thing as milligrams per liter (mg/L) When
documenting results, attempt to keep units consistent.
pH
pH can be used to determine the aggressiveness or corrosiveness of soft waters. You can
determine if weak acids are present. Acids have a concentration of hydrogen ions (H+) in
solution and a pH value below 7. Bases have a concentration of hydroxide ions (OH-) and a
pH above 7. A pH value of 7.0 is neutral, neither acidic nor basic. Pure water HOH
disassociates into equal numbers of H+ and OH- ions giving it a neutral pH of 7. Freshly fallen
rain is often acidic with a value between 5.5 and 6.0. If this water reacts with soils and
minerals with alkaline materials, the hydroxide ions will increase and may raise the pH to
around 8.0 to 8.5. Water reservoirs with a higher pH are therefore often found on surfaces
high in calcium or other similar metals.
Conduct a titration and colorimeter test using the procedure in the lid of the supply box. Be
sure all supplies are clean, dry and returned to the box when you finish. Be sure the
procedure is replaced in the lid. Review the techniques used so you may include them in your
oral report.
CARBON DIOXIDE
Although carbon dioxide in water starts a series of changes that are often troublesome, such
as corrosion, bringing calcium, magnesium, iron and other minerals into solution, it is important
to life. In soils carbon dioxide and weak organic acids produced by the roots of plants and
bacterial processes in the soil make minerals soluble and available to plants. These weak
acids quicken the pace of weathering and are important in the production of fertile soils.
Aquatic plant life depends on carbon dioxide and bicarbonates in water for growth.
Microscopic plant life suspended in water as well as larger rooted plants use carbon dioxide in
photosynthesis. One product of photosynthesis is oxygen gas. The other products are organic
compounds. The carbon for all these materials comes mostly from carbon dioxide in the
water.
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LIMNOLOGY TESTS
As carbon dioxide is taken in for photosynthesis, the alkalinity of the water as well as the pH
will rise. Aquatic animal life in the aquarium will produce opposite effects. Fish, snails, insect
larvae, worms and bacteria combine oxygen with the organic matter they eat to produce
carbon dioxide. This process is called cellular respiration. Respiration also occurs in plants,
but at a much lower rate than photosynthesis.
Conduct a titration and colorimeter test using the procedure in the lid of the supply box. Be
sure all supplies are clean, dry and returned to the box when you finish. Be sure the
procedure is replaced in the lid. Review the techniques used so you may include them in your
oral report.
DISSOLVED OXYGEN
An important atmospheric gas in water is oxygen (O2). Oxygen works with carbon dioxide in
the living processes of cellular respiration and photosynthesis. Oxygen is important in
determining the corrosiveness of water. A slightly acidic water with both oxygen gas and
carbon dioxide will be corrosive.
The measurement of oxygen in water is important because it is one of the practical indications
of purity. Organic polluting materials added to water consume oxygen and most of the
aesthetically objectionable qualities of polluted water that we notice are related to the lack of
oxygen. These organic pollutants consume oxygen less rapidly in cold water. Photosynthetic
organisms, both microscopic and rooted plants will increased the amount of oxygen in the
water, while heterotrophic organisms will have the opposite effect. Other factors affecting the
dissolved oxygen levels include the temperature and salt concentration. Oxygen is more
soluble in cold waters. A simple way to test for polluted waters is test a sample, then store the
water for several days before repeating the test. Clean, natural waters will usually lose less
than 0.5 mL oxygen per liter in five days.
Animal life in water requires oxygen. The concentration varies, but an average for most fish is
at least 4.0 mg per liter. Fish are more active in warm water and will require higher
concentrations of oxygen. Additionally, increases in carbon dioxide reduces the pH of water.
Fish cannot take up oxygen as rapidly in low pH waters containing carbon dioxide. Fish that
are most sensitive to decreases in dissolved oxygen will disappear first when waters become
polluted with organic wastes making more nutrients available in the food web for more tolerant
species. Therefore, in polluted waters, the numbers of some species will initially decrease,
while others species will actually increase.
Conduct a titration test using the procedure in the lid of the supply box. It is important to
collect your sample per the directions. You will need to return to the classroom to obtain
your water sample for this test. Be sure all supplies are clean, dry and returned to the box
when you finish. Be sure the procedure is replaced in the lid. Review the techniques used so
you may include them in your oral report.
FECAL COLIFORMS
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LIMNOLOGY TESTS
These bacteria are naturally present in digestive tracts, but are rare or absent in unpolluted
waters. Their presence is an indication of sewage or fecal contamination. These bacteria are
not pathogenic, but often occur with intestinal pathogens that are dangerous to human health.
NITRITES/NITRATES
Bacteria in water slowly change ammonia to nitrite and ultimately to nitrate. While we will test
only for nitrates, you can still make assumptions regarding pollution. If nitrate is precent, then
there have been no recent additions of waste from animals or fertilizer has runoff into the water
source. Because nitrates may come from different sources, it is important to observe the
surrounding area of the water source.
Conduct a titration test using the procedure in the lid of the supply box. Be sure all supplies
are clean, dry and returned to the box when you finish. Be sure the procedure is replaced in
the lid. Review the techniques used so you may include them in your oral report.
PHOSPHATES:
Phosphates may be used to measure the changes due to waste addition. All domestic wastes
contain phosphates; the concentrations are not greatly changed by treatment. Some
phosphates are added to wastes from washing powders, so phosphates can be a good
indicator of community wastes. Phosphate is used by aquatic plants and microscopic
phytoplankton. Often these plants take up phosphates so rapidly that addition of phosphorus
to the water is not detected. When algae and other plants die, the phosphorus is released
quickly and used by new growing plants. Therefore, waters are likely to test low for
phosphates in bright light and warm weather.
You will measure the amount of dissolved carbon dioxide using one method: a chemical test.
Conduct a chemical test using the procedure in the lid of the supply box. Be sure all supplies
are clean, dry and returned to the box when you finish. Be sure the procedure is replaced in
the lid. Review the techniques used so you may include them in your oral report.
HARDNESS:
Calcium and magnesium compounds are the most common causes of “hard” water. Sources
of these minerals are often erosion of rocks such as limestone. Erosion is often expedited by
acidic water conditions. Other sources of such minerals are the shells and skeletal remains of
organisms. In our homes, hard water reduces the effectiveness of soaps and detergents. In
natural water reservoirs, hard water (greater than 150 mg/l) often produce more fish and
aquatic life.
You will measure the amount of total hardness using one method: chemical tests.
Conduct a titration test using the procedure in the lid of the supply box. Be sure all supplies
are clean, dry and returned to the box when you finish. Be sure the procedure is replaced in
the lid. Review the techniques used so you may include them in your oral report.
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LIMNOLOGY TESTS
COLLECTION OBSERVATIONS:
Water in the fish tank was collected from East Cache Creek, a small stream nearly filled with
aquatic plants, small fish, insect larvae, crawfish and other small organisms. There was
evidence of deer in the area as well as snakes. Most likely many organisms typically found in
temperate grasslands frequent this creek.
This section of stream is fed from the bottom of Lake Ellsworth. The average depth of Lake
Ellsworth is 17 feet ( 5 meters ). The average clarity of Lake Ellsworth is fair to poor. Due to
the source of water, the temperatures are slightly cooler than the air temperatures. Less than
0.3 inches of rain fell in the area the day previous to the sample collection. The stream was
approximately 20 cm deep and flowed slow, but steadily.
Initially this stream is surrounded by somewhat steep, sloping natural grasslands, shrubs and a
few small trees. Eventually the stream flows through agricultural lands. The sediment on the
bottom of the stream is dark (nearly black) with a fine texture.
While the area of collection is not accessible by cars, the lake that feeds the stream is used for
boating and fishing recreation as well as a back up water supply for the City of Lawton,
Oklahoma. On the day the sample was collected, no boats were seen in the area.
After collection, the water is stored in a simulated river tank at a temperature ranging from 72
to 75 degrees Fahrenheit (22 to 24 Celsius ). Tap water treated to remove chlorine is
periodically added to this tank to maintain the water level.
The water in the stagnant tank was collected from Lake Helen. This lake is human made and
maintained in a city park. The center of the “pond” is aerated, however, the collection site was
not near the center. The immediate surrounding area is parking areas, grassy, gently sloping
areas and walking paths. However, nearby are major roads and highways.
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