Deforestation and its environmental damage, how water pollution arises and the part played by bacteria, examples of human pollution, and ten effects of air pollution

Understanding the topic

Question 4 is a four-part environmental question whose highest-scoring part asks what bacteria actually do after sewage enters a river. That part rewards a mechanism, not a general account of pollution, so each answer below gives the process first and the control measures second.

(a) What is deforestation? State the disadvantages caused to the environment due to this.

Deforestation is the large-scale, long-term removal of natural forest cover and conversion of the land to agriculture, settlements, roads, mining or other non-forest uses. It differs from carefully managed harvesting followed by effective regeneration.

Its environmental disadvantages are extensive. Forests store carbon in wood and soil; cutting or burning them releases carbon dioxide and removes a major carbon sink, intensifying climate change. Habitat loss fragments ecosystems, reduces genetic diversity and may drive plants and animals toward extinction. Without roots and leaf litter, rainfall strikes bare soil directly, increasing erosion, landslides and loss of fertile topsoil. Sediment then enters rivers and reservoirs, damaging aquatic habitats and reducing storage capacity.

Deforestation also disturbs the water cycle. Reduced transpiration can lower atmospheric moisture and regional rainfall, while rapid surface runoff increases flash flooding. In dry regions, continued loss of vegetation promotes desertification. Forest-dependent communities lose fuel, food, medicines and livelihoods, and closer contact among people, livestock and displaced wildlife may increase the risk of zoonotic disease.

Control requires protected forests, enforcement against illegal clearing, sustainable forestry, agroforestry, restoration with native species and higher productivity on existing farmland. Tree planting helps, but a plantation cannot immediately replace the biodiversity and ecological functions of an old natural forest.

(b) Explain how water pollution is produced? Describe the part played by bacteria after a river has been polluted by sewage.

Water pollution occurs when physical, chemical or biological substances enter water in quantities that damage organisms or make it unsafe for use. Major sources include untreated domestic sewage, industrial effluent, agricultural fertilizers and pesticides, oil, plastics, mining drainage, hot-water discharge and eroded sediment. Pollutants may enter through a visible pipe, called a point source, or through diffuse runoff from a broad area.

After sewage enters a river, decomposer bacteria feed on its organic matter. Their population increases rapidly and they consume dissolved oxygen during aerobic respiration. This raises the biochemical oxygen demand (BOD). If oxygen is used faster than it is replenished from the air and photosynthesis, dissolved-oxygen concentration falls. Fish and oxygen-dependent invertebrates become stressed or die. Farther downstream, once much organic material has been decomposed and water mixes with air, oxygen may gradually recover through natural self-purification.

If sewage loading is very high, water becomes anaerobic. Anaerobic bacteria then produce foul-smelling gases such as hydrogen sulphide and methane. Sewage may also carry pathogens that cause diseases and nutrients that stimulate algal blooms; decay of the algae consumes still more oxygen.

Treatment should remove solids and organic matter, disinfect effluent and, where necessary, remove nitrogen and phosphorus before discharge.

(c) State some examples of pollution caused by human activity and discuss the effects of each example.

Human activities produce pollution in several connected forms. These are parallel categories, not a sequence: one activity commonly produces several of them at once.

1. Air pollution: vehicles, power stations and industry emit particulate matter, nitrogen oxides, sulphur dioxide and carbon monoxide. These cause asthma and cardiovascular disease, reduce visibility, form smog and acid rain, and damage crops and buildings. Carbon dioxide and methane intensify climate change.
2. Water pollution: sewage, industrial chemicals, oil and farm runoff contaminate rivers and groundwater. Effects include water-borne disease, toxicity, eutrophication, oxygen depletion and death of aquatic organisms.
3. Soil pollution: pesticides, heavy metals, poorly managed landfill and industrial waste reduce soil organisms and fertility. Toxins can enter crops and become concentrated along food chains.
4. Plastic pollution: discarded packaging and fishing gear entangle or are swallowed by wildlife. Larger items fragment into microplastics that persist in water and soil.
5. Noise pollution: traffic, aircraft, construction and machinery cause stress, sleep disturbance, hearing loss and reduced concentration; wildlife communication and breeding may also be disrupted.
6. Thermal and light pollution: heated industrial water lowers dissolved oxygen and alters aquatic communities, while excessive night lighting disturbs insects, birds, turtles and human sleep cycles.

Because pollutants cross environmental boundaries, control works best as an ordered hierarchy rather than as cleanup alone:

(d) What does air pollution mean? State ten serious effects of air pollution on the environment and briefly explain how they can be reduced.

Air pollution is the presence of gases, particles or biological material in the atmosphere at concentrations harmful to health, ecosystems, property or climate.

Ten serious effects are: (1) respiratory illness from fine particles and ozone; (2) heart disease and premature death; (3) photochemical smog and poor visibility; (4) acid rain from sulphur and nitrogen oxides; (5) crop damage and lower yield from ground-level ozone; (6) forest decline and soil acidification; (7) contamination of water and food chains by deposited mercury and other toxins; (8) corrosion of buildings and monuments; (9) climate warming from greenhouse gases and black carbon; and (10) stratospheric ozone depletion by ozone-destroying chemicals, increasing harmful ultraviolet radiation.

Reduction needs action at source. Cleaner fuels, renewable electricity, energy efficiency and reliable public transport reduce combustion. Vehicles and factories require emission standards, inspection, catalytic converters, filters and scrubbers. Open burning of waste and crop residue should be restricted while providing practical collection and residue-management alternatives. Low-sulphur fuel and control of industrial nitrogen oxides reduce acid-forming emissions. Methane leaks from oil, gas, landfills and agriculture should be captured. Dust at construction sites must be suppressed, and harmful refrigerants should be recovered and replaced under ozone-protection rules. Monitoring, public reporting and urban green space support these measures, although trees cannot substitute for emission control.