Theme: Our Water Environment
Learning and Teaching Activities
Virtual investigation on water quality of a local aquatic body
Teaching Tips
Virtual investigation has the advantage that a student can view through the whole
complicated procedures of a water quality investigation. This relieves the constraints on time,
expense and safety, etc. Yet students after viewing the information can go straight into data
analysis which is the most essence of a scientific investigation. Data analysis skill is the
practice of logical thinking and scientific deduction. Also, this latter part of process also also
time for training students to learn, practise communication skill.
Objective: To master the skill in assessing water quality.
Introduction
Water has been an essential resource since the human civilization. It is used in agriculture,
industry, recreation and daily life.
We can easily access water source such as streams, rivers and lakes in Hong Kong. However,
these aquatic bodies face threats from pollution and thus are no longer available as resource
for drinking water. Besides, if they are polluted, measures have to be carried out to cleanup
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for providing an environmentally healthy condition. To monitor the water quality, various
parameters have to be measured. These include:
1.
Physical parameters: Light intensity, temperature, etc.
2.
Chemical parameters: e.g. Dissolved oxygen and pH,
3.
Biological parameters: Coliform bacteria count & total bacteria count, etc.
A field trip and the following laboratory works of an aquatic body which is an integrated
system of a natural stream and an artificial lake in The Chinese University of Hong Kong
were carried out and video – taped. This aquatic body provides a scenic view for relaxation
and a source of flushing water in the campus. In the field trip, the following parameters were
measured: light, temperature, pH, dissolved oxygen content; and water samples were
collected for experimental analysis in the laboratory. In the laboratory, total bacterial counts
and coliform bacteria counts were measured.
The whole class will view the videotape together first. The class of students will be divided
into small groups, and each group will examine one water quality parameter for data analysis.
Yet in order to have an overall assessment of the environmental quality of the aquatic body,
after individual group presentation on the data analysis for each parameter, a class discussion
will be conducted to overview the water quality together with the information of the
immediate environment for the sampling points.
Resources Provided
1.
Field site information
2.
Video-records of the field trips and laboratory works (attached file on the CD)
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3.
Class data of water qualities of the field
4.
Explanation of the parameters being measured and the analytical methodologies
(Appendix)
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Site Description
Figure 1. Sites explored in the Field Trip
The field trip was performed on 14/01/2002, a cloudy day. Water comes from a natural stream
of the hill, is stored in Weiyuan Lake and is then discharged to Tolo Harbour (Figure 1). Four
sampling points (A, B, C and D) were used to examine the water quality.
Site A is called ‘little bridge & flowing water’, where a natural stream comes from the hill
and passes. Surrounded by vegetation, the area was damp, moist and shady. Figure 2 shows
the surrounding environment of Site A.
Site B is at the middle – lower region of the stream. It is the exit of a drainage pipe (Figure 3).
The pipe collects rainwater from the hills, but it may be contaminated by sewage discharges
from nearby offices and a student canteen (Chung Chi Tang, Figure 4). Some green algae
could be found but no fishes or shrimps were observed.
Site C is located at the bridge of Weiyuan Lake (Figure 5). Trees there were not tall. An oily
layer was found covering the water surface. But there were still many fishes found.
Site D (Figure 6) is at the lower region of Weiyuan Lake that near Feng Shu Chuen Building.
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Trees and bushes were planted near the site. The water here comes from the natural stream
and the drainage pipes of the campus of The Chinese University of Hong Kong. At the outlet
of the Lake, two main pipes discharge the water to Tolo Harbour. Ducks (Figure 7) could be
seen near the site, their feces contaminated the water here.
Figure 2
Figure 4
Figure 6
Figure 3
Figure 5
Figure 7
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Data for Analysis
A class will be divided into several groups. Each group handles one parameter.
Site
Parameter
Light intensity (kilolux)
Temperature (OC)
pH
Dissolved oxygen (% saturation)
Total bacteria count (cfu/100 mL)*
Coliform bacteria count
(cfu/100 mL)*
*: cfu: colony forming units.
A
1.877
18.1
6.81
57
1630
60
B
5.213
17.3
6.95
49
10100
3900
C
7.537
19.2
5.84
28
800
20
D
7.111
18.8
6.91
9
1800
800
Discussion
In this exercise, students have to discuss one of the parameters measured (light intensity,
temperature, pH, dissolved oxygen, total bacteria count and coliform bacteria count).
Interpret the meaning of the data obtained. Correlate the data with the immediate
environment of the sampling points.
In the class discussion, try to answer the following questions:
1. Could you suggest the reasons for decline of dissolved oxygen down the stream and
Weiyuan Lake? List the possible substances that used up the dissolved oxygen in water
bodies.
2. Why were the total bacteria count and coliform bacteria counts exceptionally high in site
B along the four sites?
3. The water in this region is actually recycled as flushing water in the campus. Comment
whether this is a good environmental practice or not.
4. If the water quality in this region needs to be improved, state one possible measure and
explain its action principle.
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5. Could we simply the assessment of water quality by measuring only one parameter?
6. Suggest one improvement to this experimental investigation.
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Appendix
Physical parameters
1.
Light
Solar energy is the major source of energy for physical and biological activities in an
ecosystem. Solar radiation is also important for the formation of convection currents in a
pond. It drives primary productivity of algae and affects the growth of organisms. A light
meter will be used to measure the light intensity.
2.
Temperature
Temperature is perhaps the most commonly measured physical characterization of an
ecosystem. Water temperature strongly influences density. Water temperature also determines
the solubility of minerals and gases and regulates the distribution and abundance of
organisms. A lot of industrial wastewater is hot making the aquatic body unfavorable for
living.
Chemical Parameter
1.
Dissolved oxygen (DO)
DO is one of the most important gases in water bodies. It is required for aerobic respiration,
and low oxygen content is often an excellent indicator of organic pollution. An oxygen
profile can be produced by measuring oxygen concentrations at one – meter interval at a
number of different locations in the pond. Portable dissolved oxygen meters simply the
measurement of dissolved oxygen.
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2.
pH
The hydrogen ion concentration of water is one of the most important chemical components
of the aquatic habitat. It affects the diversity and distribution of organisms and determines the
rate of a variety of chemical reactions. There is convincing evidence that the survival and
distribution of many living organisms in aquatic environments is adversely affected by a
decrease in pH of the water. A pH meter can conveniently measure the pH of pond water.
Biological Parameters
Coliform bacterial count and total bacterial count by microbiological assays
Water pollutions render the water unsuitable for drinking or other usage, and for organisms to
live in. Numerous diseases, such as cholera and hepatitis are transmitted through the water.
The bacteria causing these diseases grow in the intestinal tract of human and animals just the
same as do the more abundant Escherichia coli and other fecal coliform bacteria. Therefore
water contaminated with fecal material is liable to carry pathogenic bacteria. To measure the
degree of fecal pollution in water, the international standard method is to determine the
existence and concentration of fecal coliform bacteria in the water sample. The total number
of various bacteria in water will provide an index for the degree of organic pollution in lake.
The Weiyuan Lake may polluted by wastewater from canteens and dormitories on campus.
Therefore fecal contamination is not unavoidable.
A serial dilution of the original water sample is required to determine the exact concentration
of the bacteria count. MFC medium and Luria Broth medium are used to determine the fecal
bacteria count and total bacteria count, respectively. MFC medium is a highly selective that
suppresses the growth of many bacteria, and faecal coliform bacteria give blue colonies on it.
Thus MFC medium allows an accurate estimation of fecal coliform bacteria in natural water.
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Luria Broth (LB) medium is the most commonly used rich growth medium for a variety of
bacteria. This medium provides growth factors like vitamins, amino acids, and others to
fulfill the nutrient requirements of various bacteria.
The experimental procedure is as follows:
Serial dilution for Total bacteria count & Fecal bacteria
count
1ml water sample (shake before
use)
*0.1 ml
100
*0.1ml
Each tube has 0.9ml
tryptone
broth excluding tube1
0.1 ml
10-1
0.1ml
10-1
Spread it evenly
on LB plate
0.1 ml
10-2
0.1ml
10-2
10-3
0.1ml
10-3
10-4
Another 0.1ml
on MFC plate
*Vortex during each transfer of water!
** Aseptic technique throughout the
experiment!
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