Recall

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?

Learning outcomesYou 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.

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.

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

Analyse the diagram and explain what is happening.

Starter

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

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.

Source of pollutant BOD (mg dissolved oxygen needed l-1)

Unpolluted river <5Treated sewage 20-60Raw domestic sewage 350Cattle slurry 10,000Paper pulp mill 25,000

Test yourselves

Factory Volume of Effluent / 1000 l day-1

BOD / mg l -1

A 14.0 27B 1.0 53C 3.0 124D 0.8 331 Explain whether these pollution data are for point source or non-

point sources.

2 Which pollution source, point source or non-point source is easier to regulate? Explain your choice.

3 Which factory is adding most to the BOD of the river into which it discharges?

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.

Indirect methods of measuring pollution

BOD Abiotic factors Biotic factors

Pollution Indicators What are pollution indicators? The organisms in polluted water tell you

that there is something wrong.

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.

Examples of pollution indicators

Some invertebrates like bloodworms and rat-tailed maggots, are able to survive in polluted waters

Examples of pollution indicators While others like mayfly

nymphs and stonefly nymphs can only be found in very clean water.

This is what happens when a stream or river becomes polluted

1. Pollutant is added, which kills some living things.

2. Micro-organisms decompose them, they respire and use up the oxygen

3. Lack of oxygen kills other organisms, but a few species stay alive

4. As the water flows, oxygen levels gradually increase

5. Other living things recover too.

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

100-200 Slight smell beginning to clear

Flatworm caddis fly larva Gradually rising

200+ Clear Stonefly larva mayfly larva

Freshwater shrimp

Back to normal

Sewage pollution and invertebrates

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

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

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

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

Freshwater Mite

Tiny animals related to spiders.

Up to 8mm. They have an oval body

and 8 legs. Many are brightly

coloured. BMWP = 4

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

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

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

This shows freshwater fauna as indicators of river pollution.

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:

Our Group’s findings:

Roles: Julio = scribe, Emilia = rain analyst, Rodrigo = particulate analyst, Melanie = photographic investigator, Megan = Freshwater species investigator.

1. pH testing of rain samples using UI paper2. Analysis of particulate levels using dust collector cards & hand lenses – given % cover score3. Research into lichens & analysis of photographic evidence – given score of

present/absent/abundant4. Research into preferred habitats of freshwater species, and analysis of communities present

Example of how to present your findings:

Our Group’s methods:

What we would do next to help the polluted areas:

Monitoring Pollution

Area pH of Rain Particulate % Lichen score

Freshwater species present

Rank 1-4

ABCD

- 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

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.