10.1 Threats to the Environment
Learn how human activities threaten environmental sustainability through climate change, deforestation, eutrophication, and various types of pollution.
Learning Objectives
- Define environmental sustainability and explain its importance.
- Explain the causes and effects of climate change and global warming.
- Identify the greenhouse gases involved in human activities and differentiate between the natural and enhanced greenhouse effect.
- Describe deforestation, its purposes, and its negative consequences on biodiversity and biogeochemical cycles.
- Explain the process of eutrophication and its relationship with Biochemical Oxygen Demand (BOD).
- Describe the method of determining the level of water pollution using BOD and methylene blue solution.
- Identify the sources, pollutants, and impacts of air pollution, acid rain, thermal pollution, and noise pollution.
- Discuss the impacts of the human population growth explosion on natural resources and the environment.
The Mechanism and Sequence of Eutrophication
A step-by-step flow showing how nutrient runoff triggers an algal bloom, leading to oxygen depletion and aquatic death.
1. Runoff
Excess nitrates and phosphates from fertilisers, detergents and sewage wash into rivers and lakes.
2. Algal Bloom
High nutrient levels stimulate rapid algal growth, forming a thick layer that blocks sunlight.
3. Plant Death
Submerged aquatic plants cannot photosynthesise and die. Dissolved oxygen levels decline.
4. Decomposition
Decomposer bacteria multiply rapidly, breaking down dead matter and depleting remaining oxygen. BOD increases drastically.
Short Explanation
Definition of Environmental Sustainability
Environmental sustainability refers to an environmental condition that remains stable without any reduction or depletion of natural resources, ensuring the surrounding environmental quality is maintained over a long period. It ensures current human demands are fulfilled without compromising future generations.
Recycling Bins
Using recycle bins helps sustain resources by reducing the consumption of non-renewable materials:
- Blue bin: Paper
- Brown bin: Glass
- Orange bin: Metal and plastic
Climate Change and Global Warming
Climate change refers to significant changes in global temperature, rainfall distribution, and wind patterns. The greenhouse effect traps heat energy in the atmosphere, keeping Earth warm enough for life.
Mechanism of the Greenhouse Effect
Sunlight enters Earth's atmosphere; some light reflects back into space as infrared radiation. Earth absorbs heat and re-radiates it as infrared rays. Greenhouse gases such as carbon dioxide, methane, nitrogen oxide, and chlorofluorocarbons (CFCs) absorb and trap this heat energy, preventing it from escaping into space.
Positive Effects of the Natural Greenhouse Effect
- Maintains Earth's average temperature so it is not too cold for living organisms to survive.
- Preserves life forms on Earth.
- Filters and reflects back unwanted solar energy.
- Helps in the growth of crops.
- Maintains sea levels and prevents polar ice from completely melting.
Negative Effects of the Enhanced Greenhouse Effect (Global Warming)
- Rise in Earth's average temperature.
- Melting of polar ice caps leading to rising sea levels.
- Extreme climate phenomena, such as droughts, changes in wind direction, typhoons, and storms.
- Loss of flora and fauna habitats and food sources.
- El Niño: Causes extreme hot and dry weather resulting in drought.
- La Niña: Causes unusual heavy rainfall resulting in severe floods.
Deforestation and Loss of Biodiversity
Deforestation is the large-scale clearing of wide forest areas. Its purposes include timber for construction, furniture, and paper production; mineral mining; agricultural expansion; and infrastructure, residential areas, and road construction.
Negative impacts include soil erosion and leaching, flash floods, climate change, loss of biodiversity and extinction of flora and fauna species, disruption of biogeochemical cycles (carbon, nitrogen, and water cycles), and loss of water catchment areas.
Biochemical Oxygen Demand (BOD)
Biochemical Oxygen Demand (BOD) is the total amount of oxygen required by microorganisms to decompose organic matter in water.
- High BOD: Low water quality, high organic pollution, low dissolved oxygen.
- Low BOD: Good water quality, unpolluted, high dissolved oxygen.
Experiment 10.1: Level of BOD in Different Water Samples
Aim: To compare the level of BOD in various water samples (tap water, drain water, river water, pond water, well water, and distilled water as control).
Hypothesis: Drain water has the highest BOD level.
Variables:
- Manipulated: Water samples
- Responding: BOD level
- Constant: Volume of water sample (250 ml), volume of 0.1% methylene blue solution (1 ml)
Critical Technique / Precaution: The tip of the syringe must reach the bottom of the reagent bottle when adding 0.1% methylene blue solution to prevent the solution from mixing with atmospheric oxygen. Reagent bottles must be tightly capped immediately and placed in a dark cupboard without shaking.
Principle & Measurement: Methylene blue acts as an indicator; it decolourises when dissolved oxygen is depleted by decomposers. Faster decolourisation time indicates a higher rate of oxygen consumption, meaning higher BOD and higher water pollution level.
\(\text{Rate of water pollution} = \dfrac{1}{\text{Time taken for 0.1% methylene blue solution to decolourise (hour)}}\)
| Factor | Greenhouse Gas Involved |
|---|---|
| Burning of fossil fuels | Carbon dioxide and nitrogen oxide |
| Deforestation | Carbon dioxide |
| Animal farming | Methane |
| Agricultural activities (nitrogen fertiliser) | Nitrogen oxide |
| Usage of cooling substances | Chlorofluorocarbons (CFCs) |
Air Pollution and Acid Rain
Air pollution involves elevated concentrations of atmospheric pollutants. Sources include exhaust fumes from vehicles, industrial factories, and open burning.
Acid rain is formed when sulphur dioxide and nitrogen oxide react with atmospheric water vapour to form sulphuric acid and nitric acid. Precipitation with pH lower than 5 causes soil to become infertile, root damage and leaf tissue destruction, death of plankton and fish, and human skin/tissue damage.
Thermal Pollution
Thermal pollution is the deterioration of water quality resulting from excessive heat release that raises water temperature. Industrial facilities and power plants discharge hot water used as an industrial cooling agent directly into rivers or lakes.
Consequences include decreased solubility of dissolved oxygen, disruption of metabolic and biochemical processes of aquatic organisms, early hatching or hatching failure of fish eggs, sudden death in sensitive aquatic species, and enhanced rapid algal growth which subsequently increases BOD.
Noise Pollution
Noise pollution refers to disturbing sounds that cause harmful effects on human and animal health. Sources include vehicle traffic, construction, industrial machineries, and loud music.
Health impacts include high blood pressure, depression, headaches, and hearing impairment. Human audible range: \(20\text{ Hz}\) to \(20\,000\text{ Hz}\).
Human Population Growth Explosion
Rapid increase in the total number of humans living in an area accelerates consumption and depletion of natural resources. It drives deforestation, habitat destruction, biodiversity loss, and water shortages. It also demands costly water treatment infrastructure to manage contaminated supply zones and sewage waste.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What is meant by environmental sustainability?
Explain why the tip of the syringe must reach the bottom of the reagent bottle when introducing methylene blue solution during a BOD test.
State two harmful ecological effects of acid rain.
Common Mistakes
- Confusing the natural greenhouse effect with the enhanced greenhouse effect: The natural greenhouse effect is essential for keeping Earth warm enough for life, whereas the enhanced greenhouse effect causes global warming.
- Misunderstanding Biochemical Oxygen Demand (BOD): Students often incorrectly think that a high BOD value indicates clean, oxygen-rich water. In reality, a high BOD means decomposers require a large amount of oxygen because the water is heavily polluted with organic matter, leaving very little dissolved oxygen.
- Misidentifying the causes of thermal pollution: Students sometimes link thermal pollution to global atmospheric warming rather than the direct discharge of hot cooling water from industrial plants into aquatic bodies.
- Incorrect handling during the BOD experiment: Shaking reagent bottles or introducing methylene blue from the surface exposes the water sample to atmospheric oxygen, distorting experimental results.
Concept Misunderstandings
The greenhouse effect is entirely harmful and should be eliminated completely.
Without the natural greenhouse effect, Earth would be extremely cold and unable to sustain life. The threat arises from human activities increasing the concentration of greenhouse gases, producing an excessive (enhanced) warming effect.
Eutrophication is caused directly by industrial toxic chemicals.
Eutrophication is specifically triggered by excessive nutrient enrichment, primarily nitrates and phosphates from fertilisers, domestic detergents, and sewage.
Algal blooms directly poison fish through toxic bites.
While some algae can produce toxins, the primary mechanism of widespread death during eutrophication is sunlight blockage and subsequent oxygen depletion caused by aerobic decomposers decaying dead organic matter.
Summary
- Environmental sustainability balances human resource consumption with ecosystem preservation for future generations.
- Recycling bins: Blue (Paper), Brown (Glass), Orange (Metal and Plastic).
- Greenhouse gases: Carbon dioxide, methane, nitrogen oxides, and CFCs trap infrared radiation. Excessive emissions lead to global warming and climate extremes.
- Deforestation destroys habitats, triggers soil erosion, causes flash floods, and disrupts the nitrogen, carbon, and water cycles.
- Eutrophication: Nutrient runoff \(\rightarrow\) algal bloom \(\rightarrow\) reduced sunlight penetration \(\rightarrow\) aquatic plant death \(\rightarrow\) bacteria decompose biomass \(\rightarrow\) oxygen depletion \(\rightarrow\) high BOD.
- BOD: Indicator of organic water pollution; a shorter decolourisation time of methylene blue signifies higher BOD and worse pollution.
- Major pollution types: Air pollution (acid rain, smog), thermal pollution (heated industrial discharge depleting dissolved oxygen), and noise pollution (auditory and health disturbances).
Short Activity
Objective: test your understanding of greenhouse gases, BOD, acid rain, and the factors causing the greenhouse effect.
A. Objective Quiz
Which of the following correctly pairs the greenhouse gas with the human activity that releases it?
What does a high Biochemical Oxygen Demand (BOD) value indicate about a water sample?
B. Fill in the Blanks
Precipitation with a pH value of less than 5, known as , is formed when sulphur dioxide and nitrogen oxide combine with atmospheric water vapour.
In the BOD experiment, the rate of water pollution is calculated as 1 divided by the taken for 0.1% methylene blue solution to decolourise.
C. Matching / Drag and Drop
Drag each human activity to the primary greenhouse gas it produces. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Human Activity to Its Greenhouse Gas
Write the correct greenhouse gas next to each human activity.
| Human Activity | Greenhouse Gas |
|---|---|
| 1. Animal farming | |
| 2. Deforestation | |
| 3. Agricultural activities (fertilisers) | |
| 4. Usage of cooling substances |
Answer choices: Methane • Carbon dioxide • Nitrogen oxide • Chlorofluorocarbon (CFC)
