10.1 - Threats to the Environment

Environmental Sustainability

Environmental sustainability: An environmental condition that remains the same without any reduction or depletion of natural resources, with an assured quality of the surrounding environment for a long period of time.
Ensures that current needs are met without affecting the needs of future generations.
Human population growth creates conflict between meeting human demands and conserving the environment.
Threats to the environment are caused by human activities in ecosystems; continuous threats and destruction negatively affect life.

Climate change: Changes in the Earth’s temperature, rainfall distribution and drastic changes of winds.
Global warming: The rise in the Earth’s temperature.

Sunlight enters the Earth’s atmosphere; some is reflected back into space as infrared rays.
Greenhouse gases in the atmosphere—carbon dioxide, methane, nitrogen oxide and chlorofluorocarbon (CFC)—absorb most of the released heat energy and prevent infrared rays from being reflected back into space.
The retained heat keeps the Earth warm enough for organisms to survive.
Human activities increase greenhouse-gas concentrations; more heat is trapped and the Earth’s temperature rises. This is the greenhouse effect.

Melting polar ice raises sea levels.
Drought and changes in wind direction cause storms and typhoons.
Temperature changes and loss of food sources and habitats cause loss of flora and fauna.
El Niño causes extremely hot, dry weather and drought.
La Niña causes unusually heavy rain and serious floods.

Deforestation: Clearing a wide area of trees on a large scale.
Main purposes: obtain timber; mine minerals; open agricultural areas; build residential areas and roads.
Deforestation destroys habitats and is a major cause of biodiversity loss and species extinction.
Illegal hunting for the food, medical and handicraft industries reduces animal populations and drives species to extinction.
Acid rain lowers water pH; many fish eggs cannot hatch and some adult fish die.

Air pollution: An increase in pollutants such as gases, smoke, dust and particles in the atmosphere that affects humans, animals and plants.
Main sources and pollutants:
- Vehicle exhaust fumes: nitrogen oxide, carbon monoxide, lead, smoke, soot and hydrocarbon gases such as benzene.
- Industrial smoke: sulphur dioxide, nitrogen oxide, dust, carbon monoxide and carbon dioxide.
- Open burning: carbon dioxide, smoke and soot.
Burning fossil fuels in coal-burning plants, industrial factories and vehicles releases carbon monoxide, nitrogen oxide and sulphur dioxide.
The gases combine with atmospheric water vapour to form nitric acid and sulphuric acid, which fall as acid rain.
Acid rain has a pH below 5 and:
- makes soil infertile;
- destroys leaf tissues and damages plant roots;
- reduces plankton populations, disrupts food chains and may kill organisms;
- causes skin diseases and tissue damage in humans.

Eutrophication: A process in which a water ecosystem becomes rich in nutrients, changing the ecosystem’s structure.
Sources of excess nutrients include nitrate and phosphate fertilisers, detergent residues, sewage, animal waste, domestic waste, construction sites and soil erosion from mining.
Sequence:
1. Excess nitrates and phosphates flow into lakes and rivers in rainwater.
2. Algae grow rapidly and cover the water surface.
3. Less sunlight penetrates the water; aquatic-plant photosynthesis decreases.
4. Dissolved oxygen decreases; aquatic plants and animals die.
5. Decomposer bacteria increase and decompose dead organisms using oxygen.
6. Oxygen falls further and biochemical oxygen demand (BOD) increases.

Biochemical oxygen demand (BOD): The total amount of oxygen needed by microorganisms such as bacteria and fungi to decompose organic materials in water.
High BOD: Low water quality; many organic substances and decomposer microorganisms.
Low BOD: Good, unpolluted water quality; high dissolved-oxygen content.

Comparing BOD in Different Water Samples

Aim: Compare BOD levels in water samples from different sources.
Hypothesis: Drain water has the highest BOD level.
Variables:
- Manipulated: Water sample.
- Responding: BOD level.
- Constant: Volumes of water and methylene blue solution.
Method:
1. Fill separate reagent bottles with 250 ml of tap, drain, river, pond and well water.
2. Add 1 ml of 0.1% methylene blue solution to the bottom of each bottle.
3. Cap immediately; do not shake; keep in a dark cupboard.
4. Repeat using distilled water.
5. Check hourly for four hours and record the decolourisation time.
Rate of water pollution = 1 ÷ time taken for 0.1% methylene blue solution to decolourise (hour).
Faster decolourisation → higher pollution rate → higher BOD.

Thermal pollution: Deterioration of water quality due to excessive heat dissipation into water by processes that change water temperature.
Hot cooling water from industrial factories and hydroelectric power generator plants is discharged into rivers or lakes.
Increased water temperature:
- decreases dissolved oxygen and threatens aquatic life;
- disrupts aquatic organisms’ biochemical processes;
- may cause fish eggs to hatch early or fail to hatch;
- may cause instant death in some species;
- promotes algal growth and raises BOD.

Noise pollution: Sounds that disturb and cause detrimental effects to the health of humans and animals.
Sources: Vehicles, construction activities, agricultural and industrial machinery, and loud music at gatherings.
Prolonged exposure causes stress-related health problems such as high blood pressure, cardiovascular diseases, depression and headaches.

Human population growth explosion: An increase in the total number of humans living in a certain area.
Rapid growth rapidly depletes natural resources and leads to deforestation, biodiversity loss and global warming.
Forest clearing for shelters, infrastructure, agriculture and facilities exposes organisms to limited raw and clean water, pollution, diseases and extinction.
Local water and resources may become insufficient, requiring resources to be transported from distant locations.
More sewage increases pollution; water-treatment technology raises the cost of water resources and treated water.