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Water quality analysis
There are a variety of ways to analyze
water quality. Many researchers
studying the quality of rivers use the WQI (Water Quality Index). The WQI uses nine tests to determine the
health of a river. The use of a WQI is
appropriate for high school age students and older. The following activities present ideas that
are accessible with few supplies and safe for conducting with elementary and
middle school students. They are not as
technically accurate as a WQI, however they are developmentally appropriate and
meet the objective of introducing water quality. These indicators can be monitored regularly
and graphed.
Observing
indicators
There are several ways students can observe
a body of water and begin to interpret indicators of water quality. Students can work in groups to make general
observations about the appearance of water.
They may notice a foam in the water.
Foam can be either from natural causes or man-made causes. Excessive soaps and detergents will produce
foam. Generally, this foam will not
easily break up, is more than 3 inches tall and resembles bubble bath. Natural foam is not as tall as detergent foam
and if it stirred with a stick will break apart.
Students can make observations about the
color of the water. Many times we look
into a body of water and notice a color.
However, either the color beneath the surface or reflections from the
sky generally influence such observations.
Students can guess what color the water is by looking into the body of
water. Then they can take a sample in a
clear container and compare the color with their prediction. (It may be helpful to hold a piece of white
paper behind the container to get an accurate idea of the color.)
Color can indicate many things about
water. Brown colored water is generally
the result of runoff and sediment in the water. Water that is more tea-brown in
color can be natural due to tannins released from leaf litter. Grey water is often indicative of high levels
of sewage in water. Green water can
indicate excessive algae growth.
Students can also look for obvious signs of
plant or animal life and ways in which humans have altered the area. Plants are an accessible way for students to
begin to make conclusions about the overall health of a body of water. Too many plants in the water may indicate
that fertilizers washed into the water.
Fertilizer runoff can lead to excessive growth of algae and other
aquatic plants (algal blooms). Algal
blooms can in turn affect animal survival in the water. As previously mentioned, an algal bloom can
be identified when algae in water becomes so dense that the water is colored
green.
Students can look at a body of water and
make observations about the clarity of the water. The measure of the cloudiness of water is
called turbidity. Matter that is
suspended in the water (silt, clay, microscopic life) causes turbidity. Excessive long-term turbidity can cause
problems for aquatic organisms because it changes the amount of light that can
penetrate the water. If you are
examining slow moving deep water, students can use a devise called a Secchi
disk to evaluate turbidity. This simple
device is a black and white disk on a string that is lowered into the water
until you cannot see it anymore. A
Secchi disk can be made using a compact disk and black and white paint
(waterproof paint!), and then attaching rope. There are measurements on
the rope of the Secchi disk that represent the water depth. The measurement of the depth (in meters) at
which it is no longer visible is called the “Secchi depth”. If your class is analyzing quick moving
shallow bodies of water, a Secchi disk will not work. There is a tool called a turbidimeter that is
used to measure turbidity in these instances.
Regardless of whether or not you actually
measure turbidity with your students, it can be interesting to analyze water cloudiness with your students. Why might the water be cloudy? There are numerous reasons, including soil
erosion (possibly due to construction), bottom-feeding fish stirring up
sediment, recent rainfall or flooding, excessive algae, point source pollution,
and more. Students can examine the
environment of this component of the watershed and investigate potential sources
of turbidity. Students can try to describe
the turbidity using the following scale of “clear”, “cloudy”, or “murky”.
·
Clear
indicates it is easy to see the bottom,
·
Cloudy
indicates that more than 4 inches below the surface can be seen but not the
bottom,
·
Murky
indicates that less than 4 inches below the surface can be seen.
Temperature
Temperature of water is very important
when studying water quality. The
temperature of water effects the life that can live there. One reason for this is that warmer water has less
oxygen, and colder water has more oxygen (gases are more easily dissolved in
cool water). Depending on the ability level of your class, you might begin by
having students brainstorm ideas about how water temperature could be an
indicator of different kinds of life in the water. There are actually state temperature
requirements for areas considered “cold water fisheries” based on the fact that
more desirable fish, like trout, prefer the higher oxygen habitats that occur
in colder water. Temperature also has an
effect on the rate of photosynthesis of aquatic plants and the metabolic rates
of aquatic animals. In addition, the
life cycles of many insects are connected to water temperature changes through
the seasons.
Discuss the relevance of taking surface
vs. bottom temperature of water and analyze why at various times of the year,
and even at various times in a day, these temperatures may be distinctly
different. If possible have the students
take the air temperature first and try to predict what the water temperatures
will be. You may also want to revisit
the same location several times in one day, or at various times in the week to
look for changes in temperature.
Provide your students with thermometers
and review how to read them. The
thermometers should be suspended on a string so that they are easy for children
to lower into the water. Students should
spread out and take water temperatures in different areas of the water. Keep in mind that temperature readings change
quickly when thermometers meet with the air.
Discuss the locations and temperature readings recorded at each. Does the water temperature change in
different locations? Your class may decide on ways to determine the average
temperature of the water. What do your
results tell you about the level of oxygen in that area? What do theses results indicate about the
kinds of life that may be present in that area of the stream? Is the temperature in a stream similar to
that in a pond at the same time of day?
Why or why not?
Many factors affect water temperature and
some are more obvious than others for students.
Plants that are near the edge of the water provide shade and help keep
temperatures cooler. Surfaces that are
paved will have the opposite effect.
These paved surfaces heat up quickly and the rainwater that runs off
becomes warm quickly. Another reason for
higher temperatures is industrial usage.
Some industries use water for cooling and then return it to a body of
water. This returned water is much warmer
than the surrounding water. This is
referred to as “thermal pollution”.
Benthic
Macroinvertebrate study
An exciting way to engage students in
thinking about the health of a body of water is to begin a benthic
macroinvertebrate study. “Benthic” means
bottom-dwelling and “macro” means able to see with the unaided human eye;
invertebrates are animals without backbones.
These are aquatic animals that crawl upon or attach themselves to the
substrate at the bottom of a body of water.
This type of study is also referred to as “biological monitoring”. It refers to the collection, identification,
and analysis of macroinvertebrates to determine the health of a body of
water.
Macroinvertebrates are an indicator of
water quality partly because they cannot easily escape pollution by swimming
away the way a fish can. Also, in many
types of habitats there are certain species that are more sensitive to changes
than others (as in the canary in the coal mine scenario). Many macro-invertebrates are extremely
reactive to such changes in water quality.
Consequently, the types of organisms counted can be compiled into a
biotic survey, which can indicate the health of a stream or river.
Water quality can go up and down quickly
and this may not always be caught with other types of sampling. If, for example, pollutants are being
released into a flowing body of water during the night, it may not be obvious
with other types of testing the following day.
However, the types of living macro-invertebrates will change in such a
situation. Benthic surveys are most
commonly done with streams or rivers, although you can certainly sample the
life in any wet area to gain an understanding of aquatic invertebrates living
there.
Students will need nets, buckets, white
plates, pencils, paper, classification sheets (see appendix 2), small spoons or stirrers. You might also want to bring magnifying
lenses, blank paper to record and sketch observations, and field guides. Students use their nets to strain through the
water and more importantly, the sediment at the bottom of the stream. (Be sure to stress basic rules for examining
live animals!) Students may assume that
there is “nothing” in their water/sediment sample. Explain that when the sediment settles, they
might see different macroinvertebrates moving around. One way to be most successful in discovering
macroinvertebrates in a sample of mud is to simply set down the container and
leave it undisturbed for a minute. If
students look closely they may see movement first and then notice the animals.
Your students can form small groups to
explore the samples and examine them for any species. When each group has examined the sample they
should tally the number of species that they find in their sample. Individual
student lists can be saved to compile into a class tally sheet. The classification sheet in the appendix has
sample animals that are separated into three categories. Group 1 Taxa can only be found in good
quality water as they are very sensitive to pollution. Group Two Taxa can be found in fair quality water, as they are more
tolerant of pollution, and group three Taxa can be found in any quality of
water.
Some key questions include: What do the results tell the students about
the water? Would there be different
results at different locations? Would a
pond have different animals from a stream? If you have microscopes available
you may also look at the microinvertebrates in a water sample and make
comparisons between the micro and macroinvertebrates in the water. Return the animals safely by gently lowering
the container into the water and tilting it to let the animals out. Samples should not be kept out of water long
because of the stresses of temperature change.
pH
When we measure the “pH” of water, we are
measuring the hydrogen ion concentration of the water. A measure of 7.0 is completely neutral. Anything less than 7.0 is acidic and more
than 7.0 is basic. Each whole number
difference in the pH scale represents a change of 10 times. For example, a pH of 4.5 is 10 times more
acidic than a pH of 5.5. pH is important
to consider when testing water because many plants and animals can only live in
certain ranges of pH and are susceptible to sudden changes. Most aquatic animals need water with a pH in
the neutral range between 6.5 and 8.3.
Consequently, water with a pH in this range has the greatest diversity
of life.
There are several reasons that pH may
change, but acid rain is the main reason that students will be familiar
with. Acid rain occurs when atmospheric
moisture mixes with gases that cause the moisture to be more acidic than
normal. This is often due to burning of
fossil fuels (particularly by industries) and exhaust from cars. The
To measure pH, collect water as far from the
bank as possible and below the surface of the water. One method to test pH uses pH paper
strips. These strips are inexpensive and
easy to use, though not always accurate.
Simply dip the strips into water and look for a color change. Compare the color of the strip to the chart
on the side of the container to determine pH.
Students can also dip pH strips into a common acid (such as vinegar) and
a common base (such as baking soda) to see changes. “Alkalinity” is the acid neutralizing
capacity in a substance. There are test
strips that measure alkalinity as well.
Older students might also look at ways that alkalinity buffers the
environment against acid rain.
Velocity
The intensity
of the current of a stream or river is controlled by four factors: its depth,
the slope of the land, the width of the water and the roughness of the
bottom. A combination of the velocity
of moving water and the volume of the water contribute to the water’s
flow. The flow of a body of water
affects the concentration of a variety of substances in the water, including
dissolved oxygen and pollutants. It also
affects which animals can live in the water, as not many types can adapt to
fast flowing water. Students can measure
flowing water by measuring a length of 25 feet along the edge of a river or
stream. Place an orange on the water and
time how long it takes to float the 25 feet.
The formula to determine the speed of the water is as follows:
D = distance in feet
T= total time to float 25 feet
in seconds
D / T = (number of feet the
orange floated each second)
For example:
If the orange floated 25 feet in 50
seconds the equation would be:
D=25
and T=50. The result is 25 / 50 or 1 /
2. The orange floated ½ foot (6 inches) each second.
It is most accurate if students conduct
this activity three times and then calculate the average velocity. Once students have calculated the velocity of
a stream or river, discuss some key questions: What does this information tell
us? Why would this information vary
during the year?
“We abuse land because we view it as a
commodity belonging to us. When we see
land as a community to which we belong, we may begin to use it with love and
respect.”