2. Detection and Monitoring
Environmental monitoring describes the processes and activities that need to take place to characterize and monitor the quality of the environment.
Environmental monitoring is used in the preparation of environmental impact assessments, as well as in many circumstances in which human activities carry a risk of harmful effects on the natural environment.

3. Direct Measurement
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.

4. Indirect Measurement
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 
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. For example: leafy lichens on trees if the air is unpolluted

6. Biochemical Oxygen Demand (B.O. D.)
The biochemical oxygen demand is a measure of the total demand for oxygen by living and chemical components in a water body. 
The greater the amount of polluting organic matter, the more microbes are required to break it down. (So, high dissolved oxygen, high levels of pollution) 

8. Why is B.O.D. useful?
Measuring BOD is a very useful when examining the health of water, e.g. stream, rivers and lakes. 
BOD is essentially the amount of dissolved oxygen required to break down organic materials in a given volume of water through aerobic activity. 
Essentially it is a measure of oxygen uptake in water.

9. How to calculate BOD
Determined by the number of aerobic organisms and their rate of respiration.
The greater the amount of organic pollutant in the water the more microbes are required to break it down. Hence, there is a positive relationships between pollutant level and BOD

10. How to measure BOD? Take a sample of water at measure volume
Measure the oxygen level
More the sample in a dark place at 20 degree for five days
After five days re-measure the oxygen level
BOD is the difference between the two measurement

11. What does this mean?
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
Eutrophication causes high BOD!!!!

12. Indicator Species
Biotic index is a scale 1-10 that gives a measure of the quality of an ecosystem by the presence and abundance of the species living in it.
The Trent Biotic Index is based on the fact that certain species tend to disappear and the species diversity decreases as the organic pollution in a water course increases.
The scale corresponds to the four basic water quality (Excellent, Good, Fair or Poor). 

14. Why is this a good method?
Using this index and indicator species is another indirect method of measuring pollution.
The pollutants are not measured directly but their effect on biodiversity is measured. 
Aquatic macroinvertebrates are often used as an indicator species.
They have some general characteristics that make them very useful to assess stream health.
abundant and found in water bodies throughout the world
not extremely mobile.
carry out part or all of their life cycle within the stream or river.

15. How does it work?
The biotic index works by assigning different levels of tolerance to pollution to the different types of organisms. The types of macroinvertebrates found during sampling are grouped as: 1: Pollution intolerant: These organisms are highly sensitive to pollution. (e.g. stonefly or alderfly larva) 2: Semi-Pollution intolerant: These organisms are sensitive to pollution. (e.g. dragonfly larva or crawfish) 3: Semi-Pollution tolerant: These organisms will be found in clean and slightly polluted waterways. (e.g. snails or black fly larva) 4: Pollution tolerant: These organisms will be found in polluted, as well as clean aquatic ecosystems (e.g. leeches,bloodworms)

16.
Lichen video
Frog video