Pollution of Water Flashcards
What is Biological Oxygen Demand?
(BOD)- measures of pollutant organic material in water
- indicates amount of putrescible organic matter present in water
- low BOD- good quality water
- high BOD- polluted water- oxygen is consumed by bacteria
What is dissolved oxygen (DO)?
- consumed by bacteria
- large amounts of organic matter from sewerage are present in water
- DO- the amount of oxygen available in dissolved form in water
- DO drops to certain level- life forms cannot continue at a normal rate
- Decrease in oxygen- negative on fish and aquatic life
- Pollution reduces DO- plants cannot photosynthesise due to algal bloom
How does DO affect an aquatic environment?
-Fish kills, invasion and the growth of certain weeds cause dramatic changes in a stream or other body of water.
What are the causes of oxygen depletion?
Fertilisers- nitrates and phosphates are added to soil by farmer. Some fertiliser is washed from soil by rain into a body of water- leaching
Sewage- excellent source of organic food for bacteria and contains phosphates from detergents,
How does sewage and fertilisers affect oxygen concentration?
Water contains nutrients- supports marine life
- If more nutrinets are available from fertiliser run off or from sewage:
- Algae and other substances grow rapidly (blocks out light to plants at the bottom
- Rooted plants die- bodies provide more nutrients
- Bacteria increases
- Other organisms cannot get oxygen (must leave or they will die)
What is positive feedback?
- The change from ideal conditions causes even greater change from ideal conditions
(organisms die and bodies provide even more nutrients)
What is eutrophication?
- The accelerated ‘aging process’ of a lake due to accumulation of nutrients and organic matter.
- Becomes depleted of living organisms (Tubifex- sewage worms can respire at low oxygen levels)
What are the causes of eutrophication?
Unnaturally high levels of nutrients:
- leaching of fertilisers
- Input of raw sewage
- liquid manure (slurry) washed out of farmyards
Effects of depleted oxygen
- Causes death of fish and most invertebrates
- High nitrate levels can be dangerous to human babies
Solutions for oxygen depletion
- Treat sewage before it enters rivers
- Prevent farmyard drainage entering rivers and ponds
Control uses of fertilisers: - apply only when crops are growing
- never apply to bare fields
- do not apply when rain is forecast
- do not dispose of waste fertilisers to rivers/ponds
Bubble a stream of air through badly polluted ponds
What is an indicator species?
The presence or absence of certain living organisms can also act as an indicator of the amount of pollution.
Examples of indicator species?
Clean water- mayfly larva Low/clean- freshwater shrimp Clean water- water louse High pollution- rat- tail maggot/ sludgeworm Very high pollution- bloodworm Polluted- sludgeworm Polluted- stonefly
Where do nitrogen and phosphorous pollutants come from?
- Nitrogen- run-off from agricultural land
- Phosphorus- households and industries.
How does warm water increase growth of algal blooms?
- Increases rate of chemical reaction
- Prevents water from mixing- allowing algae to grow thicker
- Allows algae to float to the surface quicker
- Allows plants to make ATP, cell membrane
Sequence that leads to eutrophication
1- Pollution of lake 2- Raised nutrient levels 3- Increased growth rate of algae 4- Increased death rate of algae 5- Increased rate of bacteria 6- Depletion of O2 by bacteria 7- Death of fish species 8- Lifeless lake choked by algal growth (bloom)
