Studies on Turbidity, pH and Microbial Presence
in Water Water covers about three-quarters of the earth’s
surface and it is essential for all known forms of life. Some of the characteristics
that control the quality of water are the turbidity of water, pH of the water and different
types of plants and animals and their density. To Study Turbidity of Water Samples using
Secchi’s Disc Method Turbidity is the measure of the relative clarity
of a liquid. Turbidity of the water body determines the depth to which light can penetrate and
thus affects the distribution and photosynthesis of phytoplankton and macrophytes. Turbidity
can be measured using several methods. The easiest and least expensive method is through
a Secchi’s disk. Materials Required:
Secchi’s Disc tied with a rope of moderate thickness and a meter tape. Procedure: Reach the center of the pond in a small boat.
Slowly immerse the Secchi’s disc into water vertically holding the rope tightly till the
black and white segments of the disc disappear. On reaching a particular depth, the disc becomes
completely invisible. Using a pin, mark the length of the rope when
the disc disappears (say A cm). Slowly pull up the disc till the black and
white segments of the disc just reappear. Using a pin, mark the length of the rope where
they just reappear. (say B cm). Using a meter tape, find the length of A and
B. Find the mean length (Say X cm) of the rope
by the following method. X=(A+B)/2 Observation: The value of X represents the depth of the
photic zone up to which sunlight penetrates in the water body and photosynthesis takes
Students are advised to perform this experiment under the strict supervision of a teacher
to prevent danger, such as drowning. To Study the pH of Water The pH is a measure of the relative amount
of free hydrogen and hydroxyl ions in an aqueous solution. Solutions with a pH less than 7
are said to be acidic and with a pH greater than 7 are basic. The pH of pure water is
7 at 25 degree celsius. The pH value of a water sample can be determined by using universal
pH indicator solution or pH paper strips. Materials Required: A water sample from the pond, bore well and
back water, pH paper, universal indicator solution, dropper and a tile. Procedure Let’s first check the pH of water sample using
pH paper. Take a pH paper strip and dip into the beaker
that contains back water. Keep the wet pH paper strip on the tile.
Do the same procedure for borewell water and pond water.
Wait for some time to dry the pH paper. Note the colour and compare with the colour
chart given on the broad range indicator paper and get a rough estimate of pH of the sample
solution. We can observe that back water and bore well
water has pH 8 and pond water has pH 5. Let’s check the pH of the water sample using
universal indicator solution. Using a dropper take some universal indicator
solution. Put 5 drops of indicator solution into the
test tube that contains water sample. Note the colour developed and compare it with
the colour chart. We can observe that back water and bore well
water has pH 8 and pond water has pH 5. To Analyse Living Organisms in Water Sample A productive water body has high nutrient
concentrations and has a very high density of phytoplankton per unit area. These water
bodies have high amounts of nutrients and dissolved oxygen and bear a large number of
organisms at different trophic levels. You will observe these kinds of living organisms
in the water sample with the help of a microscope. Material Required: A water sample from a pond, test tube, glass
slide, cover slip, needle, dropper, filter paper and a compound microscope. Procedure: Take beaker containing pond water and pour
into a test tube. Leave the water sample undisturbed till the
sediment settles to the bottom of the test tube.
Decant the clear water, leaving concentrated sediment at the bottom of the test tube.
With the help of a dropper, transfer a drop of water from the test tube to the center
of a glass slide. Take a cover slip and place it gently on the
slide with the aid of a needle. Remove the extra water using a filter paper.
Place this glass slide on the stage of the compound microscope and view it. Observations: We can observe a large number of different
organisms in water sample.