Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Explain the causes and consequences of water pollution, including eutrophication.
• Discuss alien invasive species in South Africa and their control methods.
• Understand the causes and consequences of deforestation and soil erosion.
• Describe strategies for sustainable resource management.

Lesson summary

Human impact on the environment is a critical topic, especially in South Africa, where we face unique challenges such as water scarcity, biodiversity loss, and the impacts of climate change on vulnerable communities. Understanding these impacts is not just an academic exercise; it's essential for informed citizenship and responsible stewardship of our natural resources. Many South Africans rely directly on the environment for livelihoods (agriculture, fishing, tourism), making environmental degradation a direct threat to their well-being.

Lesson notes

Water Pollution: Water pollution occurs when harmful substances contaminate water bodies (rivers, lakes, oceans, groundwater), making it unfit for its intended use. In South Africa, key sources of water pollution include: Industrial Effluent:* Industries release a variety of pollutants, including heavy metals, chemicals, and organic waste.

Example: Mining activities often release acid mine drainage (AMD), which contaminates rivers and groundwater with toxic metals. AMD formation happens when sulfide minerals are exposed to oxygen and water, creating sulfuric acid. This acid dissolves heavy metals from the rock, releasing them into the water.

Agricultural Runoff:* Fertilizers and pesticides used in agriculture can wash into water bodies during rainfall, leading to nutrient enrichment and pollution.

Sewage and Wastewater:* Untreated or poorly treated sewage can contaminate water with pathogens, organic matter, and nutrients. Inadequate sanitation infrastructure in many parts of South Africa exacerbates this problem.

Eutrophication:* This is the enrichment of water bodies with excessive nutrients, primarily nitrogen and phosphorus. These nutrients stimulate the excessive growth of algae (algal blooms). When these algae die, their decomposition consumes large amounts of oxygen, leading to oxygen depletion (hypoxia) in the water. This can kill fish and other aquatic organisms. Eutrophication is often caused by agricultural runoff and sewage discharge. For example, the Hartbeespoort Dam has been affected severely by eutrophication due to pollution from upstream sources.

Alien Invasive Species: These are organisms introduced to an area outside their natural range, where they establish and spread, causing harm to the environment, economy, or human health. South Africa is particularly vulnerable due to its diverse ecosystems.

Examples:* Water Hyacinth (Eichhornia crassipes):* An aquatic plant that forms dense mats on the surface of water bodies, blocking sunlight, reducing oxygen levels, and impeding navigation.

Black Wattle (Acacia mearnsii):* A tree that invades grasslands and forests, outcompeting native vegetation and reducing biodiversity. It uses a lot of water, impacting water resources.

Indian Myna (Acridotheres tristis):* An aggressive bird that competes with native birds for nesting sites and food.

Control Methods:* Biological Control:* Using natural enemies (e.g., insects, fungi) from the alien species' native range to control its population.

Example: Using weevils to control water hyacinth.

Chemical Control:* Using herbicides to kill invasive plants. This method needs to be carefully managed to avoid harming non-target species.

Mechanical Control:* Physically removing invasive species (e.g., hand-pulling weeds, cutting down trees). This can be labor-intensive but effective for small infestations.

Deforestation: Deforestation is the clearing of forests for other land uses, such as agriculture, urbanization, and logging.

Causes:* Agriculture:* Clearing forests to create farmland.

Logging:* Harvesting trees for timber, paper, and fuel.

Urbanization:* Clearing forests to build cities and infrastructure.

Mining:* Clearing forests to access mineral resources.

Consequences:* Biodiversity Loss:* Forests are home to a large proportion of the world's species. Deforestation destroys habitats and leads to species extinction.

Climate Change:* Trees absorb carbon dioxide from the atmosphere. Deforestation releases this stored carbon back into the atmosphere, contributing to global warming. Deforestation also reduces the amount of carbon dioxide that can be absorbed.

Soil Erosion:* Tree roots hold the soil together. Deforestation exposes the soil to wind and rain, leading to soil erosion.

Water Cycle Disruption:* Forests play a role in the water cycle. Deforestation can reduce rainfall and increase the risk of droughts.

Soil Erosion and Land Degradation: Soil erosion is the removal of topsoil by wind or water. Land degradation is the reduction in the productive capacity of land.

Causes:* Deforestation:* As mentioned above, removing tree cover exposes the soil to erosion.

Overgrazing:* Excessive grazing by livestock can remove vegetation cover, leading to soil compaction and erosion.

Unsustainable Agriculture:* Practices such as monoculture (growing the same crop repeatedly) and excessive tillage can deplete soil nutrients and increase erosion.

Climate Change:* Changes in rainfall patterns and increased frequency of droughts can exacerbate soil erosion.

Consequences:* Reduced Agricultural Productivity:* Soil erosion removes the fertile topsoil, reducing crop yields.

Water Pollution:* Eroded soil can pollute water bodies with sediment and nutrients.

Desertification:* In severe cases, land degradation can lead to desertification, where fertile land turns into desert.

Sustainable Land Management Practices:* Terracing:* Creating level platforms on slopes to reduce water runoff and erosion.