Transcript 5.2 Detection and Monitoring of Pollution

5.2 DETECTION AND
MONITORING OF POLLUTION
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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
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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.
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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
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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
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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
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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.
Diatoms
Fecal Coliform
Blue-green algae
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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.