Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Explain human impacts on biodiversity in South Africa.
• Describe the causes and consequences of deforestation.
• Evaluate the impact of water pollution and eutrophication.
• Analyse the causes and consequences of climate change.
• Discuss sustainable resource management strategies.

Lesson summary

This week we delve deeper into the critical and far-reaching topic of human impact on the environment. This is not just abstract science; it is directly relevant to every South African's life. From the air we breathe and the water we drink to the food we eat and the future we build for our children, human actions have profound and often detrimental effects on the environment. Understanding these impacts is crucial for developing sustainable practices and mitigating the damage already done.

Lesson notes

2.1 Biodiversity Loss: Biodiversity refers to the variety of life on Earth, encompassing genetic diversity within species, species diversity, and ecosystem diversity. Human activities are the primary driver of biodiversity loss, impacting ecosystems across South Africa and the globe.

Habitat Destruction: This is the single greatest threat to biodiversity. As human populations grow, natural habitats are converted into agricultural land, urban areas, industrial sites, and infrastructure (roads, dams). South Africa's rich biodiversity is particularly vulnerable to habitat loss due to mining activities, deforestation for agriculture and fuel, and urban sprawl. For example, the fynbos biome, a highly diverse and unique ecosystem found only in South Africa, is under severe pressure from agriculture and urban development.

Poaching: The illegal hunting and trade of animals for their parts (ivory, rhino horn, bones, etc.) drastically reduces populations and can lead to extinction. Rhinoceros poaching is a significant problem in South Africa, driven by demand from Asian markets. Elephants are also targeted for their ivory. The loss of these keystone species can have cascading effects on ecosystems.

Alien Invasive Species: These are species introduced (intentionally or accidentally) to an area outside their natural range. Without natural predators or diseases, they can outcompete native species for resources, disrupt food webs, and alter ecosystem functions. South Africa is particularly vulnerable to invasive species due to its diverse climate and high biodiversity. Examples include Australian acacia trees that outcompete indigenous vegetation for water and sunlight, and water hyacinth that chokes waterways, impacting aquatic life and water supply.

Pollution: Air, water, and soil pollution can directly harm organisms and disrupt ecosystems. Industrial emissions, agricultural runoff, and sewage discharge contaminate the environment with toxins and excess nutrients.

Example: The Impact of Mining on Biodiversity South Africa is rich in mineral resources, leading to extensive mining operations. Consider a hypothetical coal mine expansion in a previously pristine grassland ecosystem.

Habitat Destruction: The mining activity directly destroys the grassland habitat, displacing or killing plants and animals.

Water Pollution: Acid mine drainage (AMD) occurs when water reacts with sulfide minerals exposed during mining, creating sulfuric acid. This acidic water contaminates nearby rivers and streams, harming aquatic life.

Soil Pollution: Mining activities can release heavy metals into the soil, contaminating it and making it unsuitable for plant growth.

Air Pollution: Coal dust from mining operations can pollute the air, affecting human health and contributing to respiratory problems. This example demonstrates the multifaceted impact of a single human activity on biodiversity. 2.2 Deforestation: Deforestation is the clearing of forests for other land uses, such as agriculture, urbanization, and logging. It has significant environmental consequences.

Carbon Cycling: Forests act as carbon sinks, absorbing carbon dioxide (CO2) from the atmosphere during photosynthesis. Deforestation releases this stored carbon back into the atmosphere, contributing to climate change. Burning trees further exacerbates the problem by releasing additional CO

2. Soil Erosion: Tree roots hold soil together, preventing erosion. Deforestation leaves soil exposed to wind and rain, leading to increased erosion. This erosion can reduce soil fertility, pollute waterways, and contribute to sedimentation in dams and rivers.

Water Resources: Forests play a crucial role in the water cycle. They intercept rainfall, reduce runoff, and promote infiltration into the ground. Deforestation can reduce water infiltration, leading to decreased groundwater recharge and increased flooding.

Example: Deforestation for Agriculture in KwaZulu-Natal Imagine a farmer clearing a patch of indigenous forest to plant sugarcane.

Reduced Carbon Sequestration: The forest's ability to absorb CO2 is lost. Burning the trees releases stored carbon into the atmosphere.

Increased Soil Erosion: The exposed soil is vulnerable to erosion, especially during heavy rainfall. This erosion can lead to sedimentation in rivers and streams, impacting water quality and aquatic life.

Decreased Water Availability: Reduced infiltration of rainwater can decrease groundwater recharge, potentially affecting water availability for local communities and ecosystems. 2.3 Water Pollution and Eutrophication: Water pollution is the contamination of water bodies with harmful substances. Eutrophication is a specific type of water pollution caused by excessive nutrient enrichment, often from agricultural runoff and sewage discharge.