ESS Topic 5.2 - Detection and Monitoring of Pollution
5.2 Detection and Monitoring of Pollution
5.2.1 Describe two direct methods of monitoring pollution.
You should know one method for monitoring air pollution and another method for
monitoring either soil or water pollution.
• air pollution • measure the acidity of rain water to determine levels of
• measure CO2, CO, or NOx levels in the atmosphere using a gas sensor
• measure particulate matter suspended in the atmosphere
soil
pollution
•
• conduct tests for nitrates and phosphates according to the test manufacturer’s
instructions (refer to the LaMotte tests we have in class)
• measure the level of organic matter in the soil
water
pollution
•
• nitrate and phosphate tests
• fecal coliform tests
• tests for heavy metals
5.2.2 Define the term biochemical oxygen demand (BOD) and explain how this
indirect method is used to assess pollution levels in water.
• Biochemical oxygen demand (BOD) is the amount of oxygen required to support
respiration by organisms living in a water sample.
• high BOD indicates there are many organisms using oxygen for respiration
• low BOD indicates relatively few organisms needing oxygen for respiration
• high BOD = low DO levels = high pollutant levels, especially nitrate & phosphate
• low BOD = high DO levels = low pollutant levels
5.2.3 Describe and explain an indirect method of measuring pollution levels using a
biotic index.
• We can measure pollution levels 2 different ways: we can measure the pollution itself
directly, or we can use some other factor that is correlated to pollution levels as an
indirect indicator of those pollution levels.
• Trent biotic index - Here is what I found about the Trent Biotic Index:
“The Trent Biotic Index was first published by Woodiwiss (1964) who was employed
by the Trent River Authority (England)....Hand samples and kick samples taken with
a hand net (780 micron mesh) are taken in such a way as to include material from
all microhabitats. He devised a scheme in which the number of groups of defined
benthic [on the bottom under a body of water] taxa was related to the presence of
six key organisms found in the fauna. These organisms were plecopteran larvae,
ephemeropteran larvae, trichopteran larvae, Gammarus, Asellus and tubificids plus
red chironomid larvae. In practice, organisms are sorted into groups and streams
are classified (10 for clean water to 0 for grossly polluted) according to the presence
or absence of key groups and the diversity of fauna. This index like the saprobic
system does not take into account the relative abundance of the organisms present.
Balloch et al. (1976) reviewed the Trent Index and listed a number of advantages
and disadvantages associated with its use. Most notable advantages mentioned
were ease of use and its ability to correctly classify moderate to grossly polluted
waters. In general Balloch et al. were very critical of this index and indicated that it
was not suitable for use as a criterion of water quality because of its general
insensitivity to varying levels of impact, especially mildly and moderately polluted
International School of Tanganyika IBDP ESS 2010-2011
Instructor: Mr Brad Kremer
ESS Topic 5.2 - Detection and Monitoring of Pollution
waters. When compared to the Chandler scores (CBS and ACBS noted below) the
Trent index proved of little value in determining intermediate levels of pollution in
rivers known to have a well defined spatial pattern from clean to grossly polluted
conditions (Murphy 1978). Both Murphy (1978) and Balloch et al. (1976) also
suggested that the Trent Biotic Index was affected by habitat quality making
interpretation of the index difficult. Overall, the Trent Index appears to lack the
sensitivity desired by most workers interested in assessing the degree of biological
impairment associated with various levels of water quality.” (Source:
http://www.cpcb.ku.edu/datalibrary/assets/library/KBSreports/KBSRept35b.pdf )
• In summary:
• the Trent Biotic Index uses the presence or absence of 6 key organisms
(plecopteran larvae, ephemeropteran larvae, trichopteran larvae, Gammarus,
Asellus and tubificids plus red chironomid larvae) to indicate the relative level of
pollution in a stream.
• Advantage: Easy to use, especially for moderately or heavily polluted sites.
• Disadvantages: not specific enough, doesn’t fully account for habitat quality
• We can also use “abiotic factors that change as a result of the pollutant” to indirectly
test the pollution levels such as dissolved oxygen (DO) or BOD levels of the water (IB
ESS Course Companion p.278).
• Indicator species are those species that are present either only in polluted areas or
only in unpolluted areas. Refer to p. 280 of the Course Companion. For example…
• freshwater shrimp
• freshwater mussels
• stonefly nymphs
• caddisfly larvae
• rat-tailed maggot and sludge worms in polluted water
• peppered moth wing color (predominantly black indicates high levels of soot
and particulate matter in the air; predominantly light grey indicates relatively
particulate-free air)
• Gammarus - small crustaceans that are sensitive to different salinity levels
• Asellus - another small freshwater crustacean, which is relatively tolerant of
pollution, and therefore an indicator of polluted sites
International School of Tanganyika IBDP ESS 2010-2011
Instructor: Mr Brad Kremer