1. Recall How can we monitor air, water and soil pollution?
Write down what BOD stands for and the definition.
How can BOD be used to identify pollution?

2. Learning outcomes You should all be able to:
Describe an indirect method of measuring pollution levels.
Most of you should be able to
Explain an indirect method of measuring pollution levels – biotic index
Explain how BOD can be used to assess pollution levels in water.

3. Biochemical Oxygen Demand
A measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity.

4. Biochemical Oxygen Demand
Amount of oxygen in the water required to decompose organic wastes (dead plants, leaves, grass clippings, manure, sewerage, food waste, etc.)
Indirect measure of pollution

5. Starter
Analyse the diagram and explain what is happening.

6. How can BOD be used to assess pollution levels?
High BOD means low Dissolved Oxygen for plants / fish / invertebrates.
High BOD = a lot of organic pollution
Determined by number of organisms that are present and the rate or respiration.
BOD indicates organic matter pollution

7. How to measure BOD Take a sample of water Measure the oxygen level
Place it in a dark place at 20°C for 5 days.
After 5 days measure the oxygen again
BOD = difference between 2 measurements.

8. Source of pollutant
BOD (mg dissolved oxygen needed l-1)
Unpolluted river
<5
Treated sewage
20-60
Raw domestic sewage
350
Cattle slurry
10,000
Paper pulp mill
25,000

9. Test yourselves
Four factories discharge effluent containing organic matter into rivers. The table shows the volume of discharge into the river and the resulting biological oxygen demand.
Factory
Volume of Effluent / 1000 l day-1
BOD / mg l -1 A
14.0 27 B
1.0 53 C
3.0
124 D
0.8 33
Explain whether these pollution data are for point source or non-point sources.
Which pollution source, point source or non-point source is easier to regulate? Explain your choice.
Which factory is adding most to the BOD of the river into which it discharges?

10. Indirect methods of measuring pollution
BOD
Abiotic factors
Biotic factors

11. Pollution Indicators What are pollution indicators?
The organisms in polluted water tell you that there is something wrong.

12. Examples of pollution indicators
Lichens are plants that grow in exposed places such as rocks or tree bark. Air pollutants dissolved in rainwater, especially sulfur dioxide, can damage lichens, and prevent them from growing. This makes lichens natural indicators of air pollution. For example:
bushy lichens need really clean air
leafy lichens can survive a small amount of air pollution
crusty lichens can survive in more polluted air
no lichens air is heavily polluted with sulfur dioxide.

13. Examples of pollution indicators
Some invertebrates like bloodworms and rat-tailed maggots, are able to survive in polluted waters

14. Examples of pollution indicators
While others like mayfly nymphs and stonefly nymphs can only be found in very clean water.

15. This is what happens when a stream or river becomes polluted
Pollutant is added, which kills some living things.
Micro-organisms decompose them, they respire and use up the oxygen
Lack of oxygen kills other organisms, but a few species stay alive
As the water flows, oxygen levels gradually increase
Other living things recover too.

16. Sewage pollution and invertebrates
Distance downstream from where sewage enters the river (m)
What the water is like
Invertebrates found (not drawn to scale)
Oxygen levels
Sewage enters here 0-10
Dark and cloudy v. smelly
Chironomous larva rat-tailed maggot
Falling quickly
10-100
Cloudy bad smell
Tubiflex worm mosquito larva
Very low

17. Sewage pollution and invertebrates
Slight smell beginning to clear
Flatworm caddis fly larva
Gradually rising
200+
Clear
Stonefly larva mayfly larva
Freshwater shrimp
Back to normal

18. Stonefly nymph
Stonefly nymphs prefer rocky, stony, or gravel bottoms in cool, well-oxygenated, swift- moving streams or small rivers. Any effluent that reduces the oxygen content of the stream quickly kills the nymphs.
Biological Monitoring Working Party (BMWP) = 10

19. Flattened Mayfly Nymph
These are only found in very clean water containing lots of oxygen. They absorb oxygen from the water through their gills.
They are primary consumers that eat plants and algae.
BMWP = 10

20. Cased caddis Fly Larvae
Caddisflies use silk (like butterflies) to build cases from gravel, twigs, needles, or sand. Different species build distinct cases, but they often lose them when removed from a stream.
BMWP = 8 -10

21. Cranefly Larvae
Up to four inches long with a Fleshy, plump, rounded segmented body
Its digestive track (internal organs) can be seen moving back and forth as it crawls.
No legs and the back end usually has several extensions or finger-like lobes.
BMWP = 5

22. Flatworms Flatworms are unsegmented worms with flattened bodies.
Their flatness allows them to shelter beneath stones.
Being flat increases the area of skin exposed to the water, which improves the flatworm's oxygen uptake.
BMWP = 5

23. Freshwater Mite Tiny animals related to spiders. Up to 8mm.
They have an oval body and 8 legs.
Many are brightly coloured.
BMWP = 4

24. Leeches Flat, Worm-like, segmented body.
Many are scavengers or feed on other invertebrates.
Suckers at both ends are used for attachment, feeding, and locomotion.
They swim gracefully and quickly in an up-and-down motion.
BMWP = 3

25. Red Midge Larvae (Bloodworms)
These are sometimes called 'bloodworms' because of their bright red colour, but they are not worms at all.
They are midge larvae.
They eat dead organic matter and can tolerate very low oxygen levels.
BMWP = 2

26. Tubifex Worms
These are thread-like worms that live in the mud on stream bottoms.
They are filterfeeders
They can tolerate extremely low levels of oxygen and are therefore found in polluted water.
BMWP = 1

27. This shows freshwater fauna as indicators of river pollution.

28. Let’s do some monitoring of our own…
Read the student instructions and divide the activities between the group – who will take what role?
Make sure that you have all the necessary equipment.
Visit areas A-D and decide which you think is the most polluted.
Complete your results table and method as follows:

29. Freshwater species present
Example of how to present your findings:
Monitoring Pollution
Our Group’s methods:
Roles: Julio = scribe, Emilia = rain analyst, Rodrigo = particulate analyst, Melanie = photographic investigator, Megan = Freshwater species investigator.
pH testing of rain samples using UI paper
Analysis of particulate levels using dust collector cards & hand lenses – given % cover score
Research into lichens & analysis of photographic evidence – given score of present/absent/abundant
Research into preferred habitats of freshwater species, and analysis of communities present
Our Group’s findings:
Area
pH of Rain
Particulate %
Lichen score
Freshwater species present
Rank 1-4 A B C D
What we would do next to help the polluted areas:
Find source of pollution – traffic survey & check local industry
Lobby local council to introduce traffic calming measures
send leaflets to local industry to inform them of measures to reduce the pollution produced

30. bushy lichens need really clean air
leafy lichens can survive a small amount of air pollution
crusty lichens can survive in more polluted air
no lichens air is heavily polluted with sulfur dioxide.