Transcript Detection-Monitoring-Pollution

5.2 Detection and Monitoring
of Pollution
• Direct measurement is performed by
monitoring the level of the pollutant itself,
e.g. nitrates in a lake or temperature levels
in a lake or stream. An indirect method
would monitor the effects of the pollutants
on other factors, e.g. dissolved oxygen,
B.O.D., presence or absence of indicator
species (see 5.2.3)
Some direct measurements might include:
• measuring temperature in several locations along the
length of a river, or at different times during the year with
thermometers as an indication of thermal pollution. Take
baseline measurements and then monitor in a
systematic manner to determine changes.
• measuring nitrate levels/ammonia levels/chloride levels
as an indication of nutrient overload. Use the same
process as above
• measuring TSS (Total Suspended Solids) or TDS (Total
Dissolved Solids) as an indication of material entering
the lake or stream. (see next slide)
TSS (Total Suspended Solids) or
TDS (Total Dissolved Solids)
BOD
(Biochemical Oxygen Demand)
• BOD is the measure of the amount of dissolved
oxygen that is used by aerobic bacteria to break
down the organic matter in a specific volume of
water.
• Therefore the greater the amount of organic
matter (sewage, agricultural run-off, fertilizer
etc.) in the body of water, the higher the BOD
will be. The less organic matter, the lower the
BOD. It is not uncommon for the BOD of
incoming water to a sewage treatment plant to
be in the range of 120. After treatment the BOD
of the same water is around 5.
• The standard technique for measuring the
BOD of body of water is the 5-Day BOD
test or BOD5. This is done by measuring
the DO (dissolved oxygen) on day 1 and
and again on day 5 while keeping the
samples at 200C in the dark during that
time. This ensures that only respiration is
going on and not photosynthesis. Refer to
Topic 2 under Gross and Net primary
productivity
Dissolved Oxygen Probe
• Factors Controlling BOD and DO
• A major source for DO comes from the atmosphere
• When the surface of the water is disturbed as in rapids
or water falls, then a greater the amount of oxygen will
become dissolved in it.
• Temperature is a major factor. An increase in
temperature  a decrease in DO. i.e the colder the
water the greater the concentration of dissolved oxygen
in the water.
• Low DO from man-made source of heating bodies of
water (effluent from nuclear power plants used to cool
the reactors)
• BOD is affected by respiration or lack of respiration by
microorganisms and by the increase in organic matter
(plant and animal) and organic waste and sewage.
• Organic effluent can be treated by pumping it with large
volumes of air.
BOD Level
BOD Level
(in ppm)
Water Quality
1-2
Very Good
There will not be much organic waste present in
the water supply.
3-5
Fair: Moderately Clean
6-9
Poor: Somewhat Polluted
Usually indicates organic matter is present and
bacteria are decomposing this waste.
100 or greater
Very Poor: Very Polluted
Contains organic waste.
Indirect measurement
• Indirect measurement involves the
monitoring and measurement of
organisms in the ecosystem and more
specifically indicator species or index
species. These are species that by virtue
of their abundance or absence will indicate
the level of pollution in that ecosystem.
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Some important indicators are:
fish
bottom fauna
algae
bacteria
Stonefly Adult
Sludge Worm
• Comparison of diatoms to blue-green
algae provides similar information
• Measuring the coliform levels can also
indicate the presence of sewage dumping
in the ecosystem.
Effect of Low Dissolved Oxygen
• Overall the diversity of the whole system is
often the best indicator while a general
rule to follow is that presence is better
evidence than absence.