TOPIC 10 HUMAN IMPACT ON THE ENVIRONMENT

PLEASE NOTE: Topic 10 will be part of the Gr12 syllabus. You will be tested on it during Gr12 Term Test 1, Prelim and Final exam

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During this topic we will be looking at the following: (1) Introduction

(2) Atmosphere and climate change

(2.1) Greenhouse effect

(2.2) Carbon dioxide emissions

(2.3) Climate change

(2.4) Methane emissions

(2.5) Ozone depletion and ozone as pollutant

(3) Water availability

(3.1) Natural water availability

(3.2) Construction of dams

(3.3) Destruction of wetlands

(3.4) Poor farming practices

(3.5) Droughts and floods

(3.6) Exotic plantations and depletion of the water table

(3.7) Borehole and effect on aquifers

(3.8) Wastage of water

(3.9) Cost of water

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(4) Water quality

(4.1) The use of water

(4.2) The effect of mining on the quality of water

(4.3) Eutrophication

(4.4) Thermal pollution

(4.5)The need for water purification and recycling

(4.6) Invasive alien plants

(5) Food security

(5.1) Climate change

(5.2) Poor farming practices

(5.3) Alien plant and reduction of agricultural land

(5.4) The loss of wild varieties: impact on the gene pool

(5.5) Genetically engineered/modified food

(5.6) Wastage

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(6) Loss of biodiversity (the sixth extinction)

(6.1) Habitat destruction

(6.2) Poaching

(6.3) Alien plant invasions: methods of control

(6.4) Indigenous knowledge

(7) Solid waste disposal

(7.1) Dumpsites, rubbish dumps and landfill sites

(7.2) Managing dumpsites

(7.3) The need for recycling

(7.4) Using methane from dumpsites

(7.5) Safe disposal of nuclear waste (radioactive waste)

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(1) Introduction

Humans depend on the environment for their survival. Our behaviour and the way in which humans treat the environment have a direct relationship to the survival of the human race. The problems we have caused to the environment are interrelated, as each problem does not exist on its own.

The environment is in a crisis because of the impact man has had on it. We have used and are abusing nature to such an extent that the environment is now exerting a pressure in response to our mismanagement of the resources.

If we do not solve the negative impacts we have on the environment the generations to follow will pay the price.

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(2)Atmosphere and climate change (2.1) Greenhouse effect

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The atmosphere is made up of layers of air surrounding the earth.

The sun’s energy (radiant energy) consist of:

Ultraviolet radiation (harmful to life)

Visible light (used by plants for photosynthesis, and animals for sight)

Infrared radiation (heat energy)

Not all radiant energy reaches earth’s surface. About half is reflected back out to space or absorbed by clouds and atmospheric gases. Most of the harmful ultraviolet radiation is absorbed by ozone in the upper atmosphere.

Some of the radiant energy which reach the earth’s surface is reflected back out of space by bright surfaces (snow, ice and sand).

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The rest is absorbed by the land and water on earth, and then gradually re-emitted as heat energy (infrared radiation).

This heat energy is trapped by gases in the atmosphere, and then re-released back towards the surface of earth. This warms the earth.

This is called the greenhouse effect, because gases in the atmosphere, such as the glass of a greenhouse, let sunlight through and keep the heat inside.

The greenhouse effect is a natural atmospheric phenomenon which is essential for life on earth.

Greenhouse gases are those atmospheric gases which are particularly effective at trapping the heat energy re-emitted from the surface: carbon dioxide, methane, nitrous oxide, ozone and water vapour.

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(2.2) Carbon dioxide emissions

Carbon dioxide is the most important greenhouse gas.

Carbon dioxide emissions into the atmosphere have increased dramatically over the past 50 years.

Carbon dioxide emissions

a. Burning of fossil fuels

Carbon footprint

b. Deforestation

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(a) Burning of fossil fuels

Fossil fuels (coal, crude oil and natural gas) derives from the remains of plants and animals which died and were buried under sediments millions of years ago.

Dead organic matter is rich in carbon.

When fossil fuels are burnt, they release this stored carbon into the atmosphere in the forms of large amounts of carbon dioxide.

Fossil fuels are mainly used for:

(1) electricity generation in power stations

(2) transport

(3) industrial processes

The concept of a carbon footprint: The carbon footprint of individuals, nations or organisations is the total amount of carbon dioxide they are directly or indirectly responsible for producing in a year.

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(b) Deforestation

Deforestation refers to the clearing of large areas of natural forest to supply timber and fuel, and to free up land for agriculture.

Deforestation increases the levels of atmospheric carbon dioxide in two ways:

(1) Trees act as a sink for carbon dioxide by absorbing it

during photosynthesis. If trees are cut down, they are

no longer able to do this, and so the atmospheric

levels of carbon dioxide increase.

(2) When the trees are cut down and buried or decay,

carbon trapped in the trees is released as carbon

dioxide.

Other problems associated with deforestation include:

(1) extinction of forest plant and animal species (reduces

biodiversity)

(2) possible increase risk of flooding, soil erosion and landslides.

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(2.3) Climate change

Climate refers to the average weather conditions, such as temperature, rainfall, humidity and wind, experienced by a region over a long period of time.

Climate change

Global warming

a. Greenhouse effect

b. Desertification

c. Drought

d. Floods

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Global warming

In recent decades, average temperatures around the world have increased at much greater rate than ever before. This is called global warming.

Scientist believes that global warming has been caused by the increase of greenhouse gases (carbon dioxide, methane and nitrous oxide) due to human activity.

Global warming is believed to cause greater extreme weather conditions, such as droughts, floods, storms and heat waves and also to speed up the process of desertification.

a. Greenhouse effect

Even though the greenhouse effect is a natural warming of the earth's surface, it has become uncontrollable due to the fact of an increase release of carbon dioxide.

This lead to an enhanced greenhouse effect.

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b. Desertification

Desertification means that land that was once productive for farming is being converted into desert. This usually happens when the plant cover is removed form the land due to drought or overgrazing. Without enough plant cover, rain runs off the land before it is absorbed by the soil, and humidity and rainfall decrease as there are no plants to draw water out of the soil. The nutrient rich topsoil is removed by wind erosion and new plants cannot take root.

c. Drought

Drought can be defined as a prolonged period of low rainfall which has a negative effect on plant, animal and human life.

Global warming is believed to increase the frequency and severity of droughts around the world.

During periods of drought the water table in the ground drops, causing springs and rivers to dry up and dams to empty.

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d. Floods

Flooding due to global warming take two forms:

(1) Increased rainfall

Scientist believe increased rainfall is due to global warming, because warmer sea and air temperatures cause greater evaporation leading to an increase in rainfall.

Heavy rain and flooding can cause great destruction and death to many people.

(2) Rising of sea levels

Higher temperatures affect the polar regions the most, causing polar ice to melt. The increase in water leads to a rise in sea levels. Rising of sea levels lead to flooding of low-lying coastal areas.

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(2.4) Methane emissions

Methane is a gas formed when anaerobic bacteria decomposes moist organic material.

It is highly flammable and can also be explosive.

• Fossil fuel and natural gas consist mainly of methane, which is formed by anaerobic decomposition of dead organic matter millions of years ago.

• Methane is the second most important greenhouse gas. It is less abundant than carbon dioxide but absorbs far more heat energy.

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(2.5) Ozone depletion and ozone as pollutant

Ozone (O₃) is either helpful or harmful, depending on where it occurs.

Ozone which occurs naturally in the upper atmosphere forms the ozone layer. This protects us by absorbing about 99% of the sun’s harmful ultraviolet rays (UV-B).

Ozone which occurs closer to earth acts as a pollutant. It damages plants, buildings and sensitive tissues for example eyes and lungs.

Ozone depletion:

Some air pollutants deplete (use up or destroy) the ozone layer. These pollutants are spread through the atmosphere by wind currents.

Chlorofluorocarbons (CFC’s), used in aerosol

sprays, fridges and polystyrene, cause the

most damage to the ozone layer.

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(3) Water availability (3.1) Natural water availability

Clean, fresh water is the most essential resource for the survival of all living things.

Water moves through the environment in the water cycle and falls to earth as precipitation (rain, hail, snow).

Precipitation (water in all forms) that falls on the ground:

• Evaporate

• Form surface water in streams, rivers and lakes.

• Are absorbed by plants.

• Infiltrate (seep into) the soil to form groundwater.

Groundwater fills the gaps between soil particles and rocks and the spaces inside permeable rocks until it reaches an impermeable layer of rock or clay that prevents it from penetrating more deeply.

• The area of ground that is saturated with groundwater is called a aquifer.

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• The top of the groundwater is called the water table. The depth of the water table is not fixed, but varies according to the region and the season as well as the rainfall.

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Humans use fresh water for:

Domestic purpose (drinking, cooking, washing)

Food production (agriculture, fishing)

Industry (manufacturing good)

Mining

Recreation

Human activities have an impact on water availability and quality.

South Africa receives relatively low rainfall, which varies in time and seasons.

South Africa’s constitution states that access to sufficient water is a basic human right. While people’s access to water has improved in SA in recent years, there are still problems with service delivery and water quality in many municipalities.

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(3.2) Construction of dams

Dams store water for drinking, household use, agriculture and to make electricity.

Impact on the environment:

• Changes to the natural water flow.

• Loss of habitats below the dam.

• Water quality is reduced.

• Sediment flow is changed.

• Prevents natural migration of fish up and down stream.

• Prevent deposits of nutrient rich silt downstream.

• People have to move to a new area when a dam is built.

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(3.3) Destruction of wetlands

A wetland (vlei) is an area which is usually covered with shallow fresh or brackish water and which support plants adapted to living in waterlogged soil.

Wetlands are important for:

Water purification

Reducing the risk of flooding.

Reducing seasonal changes in water levels.

Filling up underground stores of water – aquifers.

Controlling soil erosion.

Increasing biodiversity.

Wetlands are among the most threatened ecosystems in SA and in the world.

Threats include:

Being drained to make the land available for farming, plantations, infrastructure, mines of factories.

Overgrazing especially cattle – which cause loss of plant species and compressing the soil.

Invasion by alien plants, such as water hyacinth and water lettuce.

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(3.4) Poor farming practices

Soil and land need to be in good condition so that rain can run off into dams and rivers without taking topsoil with it and eroding the land.

Poor farming practices include:

• Overgrazing – animals eat the grass until the is none left. Soil is exposed and gets washed away in heavy rains. This soil is washed into the rivers and dams.

• Deforestation

• Burning of vegetation (plants)

• Monoculture – planting the same crop species on the same soil area over and over. This will deplete the nutrients from the soil.

• Overuse of fertilisers – the runoff of fertilisers will wash into the rivers/streams and cause algae to grow/boom, this will block out sun rays form entering the water and photosynthesis in the water will decrease, causing less oxygen in the water = aquatic animals to die. This is proses is called eutrophication .

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(3.5) Droughts and floods

Good storage facilities are required to trap and hold rain that falls during a flood, so that water is available during a time of drought.

Wetlands helps slow down and control flood waters.

It is necessary to have vegetation covering and holding the soil so that it does not wash away.

(3.6) Exotic plantations and depletion of the water table

It has been suggested that exotic or alien plantations take up more water than indigenous trees, drying up streams and the water table.

Plantations should be grown in places of high rainfall.

Movement of rain water is quicker through plantations, as there is not much vegetation holding the soil between the trees.

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(3.7) Borehole and effect on aquifers

The water from boreholes and aquifers is clean and safe to drink.

Boreholes must still be monitored so that:

• More water is pumped form them than what enters into them from rain. They do not become polluted of have toxic substances wash into them.

(3.8) Wastage of water

Every day millions of litres of water is wasted by the population.

It is extremely important that all people should use water in a conscious way to ensure the wastage of water can be reduced.

(3.9) Cost of water

Water carries a cost to the consumer as a result of infrastructure, maintenance, delivery and covering the salaries of the people working in that sector.

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(4) Water quality (4.1) The use of water

Water for domestic use:

• This is the water used in the home for cooking, cleaning, bathing, getting rid of human waste, watering the garden and washing cars.

• It is important to have good, clean and safe water to dink.

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Water for industrial use:

• Water is used as a raw material for example in paper making.

• Used for cooling machinery.

• Used to carry waste away from the factories.

If it is not managed carefully, these can pollute water.

Water used for agricultural use:

• More than 70% of water is used for agriculture.

• If crops don’t get enough water from rain then farmer irrigate their crops using water from rivers, streams or lakes.

• The increasing human population, along with higher living standards, needs more and more food from crops.

Water for mining:

• Used in the air conditioners deep in mines.

• Pressured water is sprayed onto rocks to extract minerals.

• Used to cool down the machinery used in mining. 28

(4.2) The effect of mining on the quality of water

Groundwater seeps form the rock into the mine. This water, which is often polluted, needs to be pumped out. It is pumped into streams and dams.

Many old mines no longer being worked have filled with acidic water. It is beginning to move out into the surface and underground water and polluting these.

Wet waste rock is pilled near the mine. Contaminated water seeps from the rocks and pollutes surface water.

The following have an impact on the quality of water:

Processing chemicals

Acid mine drainage occurs when metal sulphides from the ore react with water to make sulphuric acid.

Heavy metal contamination, such as arsenic, lead and zinc. Heavy metals are toxic to humans and animals.

Erosion can occur.

Sedimentation can occur when the powdery soil (caused by erosion) gests washed into dams and streams.

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(4.3) Eutrophication

This occurs when high nitrogen and phosphorous levels in bodies of water cause an increase in the growth of phytoplankton, algae and aquatic plants. (caused by overuse of fertilisers)

This rapid growth is called an algae bloom, turning the water green.

Aquatic plants below receives less sunlight and die, (no photosynthesis can occur) it sink to the bottom and are decomposed by bacteria.

This leads to a lack of oxygen in the water.

Animals will die as there is no oxygen.

The habitat becomes a dead zone.

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(4.4) Thermal pollution

Thermal pollution refers to a sudden increase in the temperature of the water. This can be caused by factories, mining etc. Thermal pollution is a problem because warm water holds less oxygen and it cause an increase in metabolic rate of the aquatic organisms which harms the organism.

(4.5)The need for water purification and recycling

SA is a very dry country and therefore we need to purify and recycle water. Water can be purified and recycling of water (grey water) is used.

(4.6) Invasive alien plants

Invasive alien plants is plants brought into the country, it is said that they use much more water than indigenous plants.

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(5) Food security DEF: The access to adequate, safe and nutritious food, by all people at

all times for a healthy and productive life.

(5.1) Climate change

Extreme weather conditions are caused by global warming. This reduces food security. It also poses a threat to crop production – less food for people.

(5.2) Poor farming practices

Monoculture: growing the same crop species each year. This does increase food security however there are problems with this:

Pest control: monoculture can encourage the exponential growth of pests. Pesticides are required and these can kill other organisms in the food chain.

Loss of topsoil: when one type of crop is grown every year after year the soil is depleted of nutrients. If nothing can grow on the soil, the wind will blow away the topsoil due to erosion.

Need for fertilisers: because of the loss of fertilisers, this is expensive and in turn make the produce more expensive.

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(5.3) Alien plant and reduction of agricultural land

The following reduce food security:

• When alien plants become invasive and take over suitable land for crops.

• More plantations being planted, as they are more economically productive crops.

(5.4) The loss of wild varieties: impact on the gene pool

With many people moving into urban areas there are less rural people growing wild varieties of crops. Wild varieties are often resistant to pest and diseases and can be used to breed the pest of disease resistant gene/s in to the domesticated crops.

The loss of these varieties can cause a reduction in food security.

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(5.5) Genetically engineered/modified food

These increase food security because:

• They may be resistant to pests (reduces use of expensive and poisonous pesticides)

• They may be resistant to disease caused by viruses of bacteria.

Crops are able to tolerate:

• Herbicides used to kill weeds.

• Cold temperature and not be harmed by frost.

• Drought and salty soil, therefore crops can be grown in areas that were previously unsuitable.

(5.6) Wastage

Food security can be increased if food is not wasted, food is wasted:

• At production on farms.

• After harvesting the crops.

• During the processing of the crop into food products.

• During the selling of the food products.

• From eating.

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(6) Loss of biodiversity (the sixth extinction) The only extinction caused by a biotic factor: Humans

(6.1) Habitat destruction

When natural vegetation is removed the animals living there will have to migrate to a new place or they may die. Habitat destruction van be caused by:

o Poor farming practices

o Development

o The removal of indigenous forests

o Loss of wetlands

o Loss of grasslands

o Spread of invasive alien plants 35

(6.2) Poaching

Poaching is the killing of animals to eat or sell. This threatens the animal species, especially those that are becoming rare and in danger of becoming extinct.

(6.3) Alien plant invasions: methods of control

Alien plants are not indigenous and spread very quickly and easily. They overcrowd and overtake natural habitats and destroy them .

Alien plants can be controlled or eradicated by the following methods:

• Mechanically – dig, bulldoze of chop them up

• Chemically – use of herbicides to kill them.

• Biological – using natural enemy, pests or predators such as insects to harm or eat alien plants.

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(6.4) Indigenous knowledge

Traditional health practitioners require plants to use as medicine to heal patients.

These plants are indigenous and are harvested by people.

Some of these plants are being over-harvested, thus making them threatened. They need to be harvested in a sustainable manner so that they do not become extinct.

Use HIPPO to remember the role humans play in the loss of biodiversity:

H = Habitat loss/destruction I = Invasive alien species P = Population explosion of humans P = Pollution O = Overconsumption (over-use) of natural resources

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(7) Solid waste disposal (7.1) Dumpsites, rubbish dumps and landfill sites

This is where solid waste is dumped to decompose. It is levelled with bulldozers and covered with soil.

Disadvantages of this method:

• Cannot be too close to settlements as dump sites are smelly and land is expensive.

• Transport costs increase the further they are away form cities.

• Methane gas can build up and cause fires.

• Attract disease-carrying organisms such as rats, mice and flies.

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(7.2) Managing dumpsites

Dumpsites need to be managed to prevent soil and water pollution:

• The main pollutant is water and rain seeping through the layers of waste and collecting poisonous chemicals, which dissolve in it.

• This seep into soil, groundwater and surface water, poisoning them. This cause water pollution and soil pollution.

• Prevention of pollution: can be using thick plastic or clay lining at the base of the dump.

• Rehabilitation: Once dumpsites can no longer be used they need to be rehabilitated to ensure that the land can be used for other purposes.

• Good management includes:

Dumpsites need to be far enough but not to far to make transport too expensive.

A good underground water system to filtrate the water

A system of pipes to release the methane gas accumulated

Waste should be flattened and buried with soil

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(7.3) The need for recycling

Recycling is very necessary to reduce the amount of solid waste and hence not put great pressure on making and managing more and more landfill sites.

(7.4) Using methane from dumpsites

Dumpsites produce a large amount of methane gas form the decomposition of the waste. This gas can be piped off from the dumpsite and used as a supply of alternative energy. This will reduce the greenhouse gases entering the atmosphere.

(7.5) Safe disposal of nuclear waste (radioactive waste)

Nuclear waste is very toxic and dangerous as it can remain in the environment for millions of years. Radioactive waste can destroy nucleic acids in organisms, which can result in genetic defects, cancer or even death. 40