9.3 Human activities that threaten an ecosystem Human activities often affect whole ecosystems. With great advancements in the medical field, modern farming techniques and better infrastructure, the worlds population has grown to over 6 billion today. Conflicts, therefore, arise between the need to meet the immediate human demands in the short term and the need to protect and conserve ecosystems from long-term damage. Many of the problems related to the environment are the results of human activities and human interference with the ecosystems. The negative effects of hasty, unplanned development and the mismanagement of the ecosystems result in various environmental problems such as air and water pollution, the greenhouse effect, global warming and the depletion of natural resources. These problems bring negative effects that increasingly threaten the economic resources, health and survival of ecosystems.

Human activitiesEffects on the ecosystem

Deforestation Soil erosion Landslides Flash floods Climatic changes The loss of biodiversity The greenhouse effect and the global warming

Burning of fossil fuels Greenhouse effect Global warming Air pollution

Overuse of fertilisers in intensive farming Eutrophication Water pollution

Dumping of domestic and industrial waste Water pollution

Table 9.1 Impact of unplanned human activities on the ecosystem

The impact of human activities on the ecosystem Deforestation and its effect The rapid destruction of woodlands or the removal of trees from forests is known as deforestation. Tropical rainforests have important ecological roles. a) Rainforests are the oldest ecosystems on Earth and house almost half of the flora and fauna of the world.b) They contain many unique species, which provide food, medicine and other biological products. c) Rainforests regulate climate by influencing wind, rainfll, humidity, and temperature patterns.d) Also known as carbon sink of the Earth because they absorb vast amount of carbon dioxide.e) Serve as water catchment areas. In general deforestation results in soil erosion, flash floods, landslides, disruption to the carbon and nitrogen cycles, severe climatic changes and the loss of biodiversity.Deforestation causes soil erosion, landslides and flash floods

Without proper development and planning, a land stripped of its vegetation can rapidly succumb to soil erosion.The absence of plant root systems makes the soil structure unstable. When it rains heavily for a long period of time, the top layer of the soil crumbles and this leads to landslides on steep hillsides.The eroded soil is then carried by moving water and deposited at the bottom of the river. This together with the depletion of water catchment areas will cause flash floods during rainy season.

Deforestation results in the loss of biodiversity

The destruction of millions of hectares of forest means:a) The removal of the bases of numerous food webs.b) The loss of habitats of many species.c) The extinction of countless species.

Deforestation disrupts the carbon and nitrogen cycles

The removal of plants in the rainforests disrupts the natural cycle of nutrient.The level of atmospheric carbon dioxide rises as less carbon dioxide released is remove removed by plants during photosynthesis.The level of atmospheric oxygen drops as less oxygen is released by plants during photosynthesis. The recycling of nitrates and other ions slows down.Tree roots bind soil particles together, and the tree canopy reduces the force of rain beating down on the soil. Deforestation therefore causes the loss of nutrients through leaching, and run-offs.

Deforestation causes climatic changes

Deforestation disrupts the normal weather patterns, creating hotter, drier weather, and causing global climatic changes.The removal of trees reduces transpiration, rainfall, and the rate at which plants absorb carbon dioxide from the atmosphere during photosynthesis.This leads to an increase in the carbon dioxide level in the atmosphere. High levels of carbon dioxide prevent heat from escaping from the atmosphere. This is known as the greenhouse effect which is believed to lead to global warming.Forest clearing and burning of wood result in air pollution and release more carbon dioxide into the atmosphere.Burning of trees in the tropics add about 25% more carbon dioxide to the atmosphere.

Burning of fossil fuels and its effects The burning of fossil fuels adds about 75% of carbon dioxide to the atmosphere. An increase of carbon dioxide level is associated with the greenhouse effect and the global warming.

Intensive farming and its effects Excessive use of land for intensive farming decreases the space and resources available for other species. In intensive farming, farmers often use inorganic fertilisers, which contain nitrates, phosphates and potassium ions, to improve crop yields. Since nitrate and ammonium ions are highly soluble, they do not remain in the soil for long and are quickly leached into the surrounding rivers and lakes. This leads to eutrophication. Eutrophication is discussed later in the section on water pollution.

The effects of an increase in domestic waste and industrial waste An increase in human population generates an increase in both domestic and industrial waste. The dumping of waste in landfills poses a great danger to living organisms as toxic substances and other pollutants from the dumpsites leak into the ground and eventually pollute the nearby water resources.

Pollution Pollution is an undesirable change in the physical, chemical and biological characteristics of natural environment due to human activities. There are four types of pollution: air, water, thermal and noise pollution.

Air pollution Burning of fossil fuels is the main source of air pollution. Fossil fuels are burnt in power stations using coals, petroleum and natural gas in domestic and industrial boilers, and in the internal combustion engines of vehicles. When fossil fuels are burnt, the elements in the fuels are oxidized, forming various air pollutants. These includes carbon dioxide, sulphur dioxide, oxides of nitrogen and fine particulate matter.PollutantsSourcesEffectsSolutions

Carbon monoxide(CO) Colourless, odourless gas Incomplete combustion of fossil fuels The exhausts of vehicles FactoriesHealth: Combines readily with haemoglobin and affects the transport of oxygen to the body cells. Impairs alertness, causes fatigue and headaches

Sulphur dioxide(SO2) Pungent, colourless gas Sulphur dioxide is formed when sulphuric compounds react with oxygen during combustion Combustion of fossil fuels, particularly in heat and power generation facilities. Volcanic gases Large industrial boilers FactoriesHealth: Irritates the eyes Damages respiratory passages Causes bronchitis Causes wheezing, a shortness of breath and coughing Causes asthmatic attacksClimate: Combines with rain water to form acid rainAgriculture: Contributes to acid rain which damages photosynthesis tissues Acid rain lowers pH of soil, rivers and lakes.Buildings: Acid rain corrodes iron, limestone and stonework, and destroys buildings Use low sulphur content fuels. Clean up emissions from power stations and factories with scrubbers

Oxides of nitrogen Nitrogen monoxide(NO) Nitrogen dioxide(NO2) Vehicle exhausts Actions of bacteria on fertilisers Combustion of fossil fuels FactoriesHealth: Irritate lungs, nose, throat, and eyes Cause respiratory infections Causes bronchitisClimate: Dissolved in rain water to form acid rainClean up emissions from car exhausts by installing catalytic converters to turn oxides of nitrogen into harmless nitrogen gas

Lead (Pb)Lead compounds are added to petrol to prevent the inefficient burning of the petrol-air mixture Combustion of fossil fuels Vehicle exhaust fumesHealth: Retards mental development and damages the liver Can result in coma or deathUse unleaded petrol

Carbon dioxide (CO2)An acidic, colourless and odourles gas Open burning Combustion of fossil fuelsHealth: Affects respirationClimate: Leads to greenhouse effect and global warming Results in an increase in the atmospheric temperature. Climatic changesReduce the use of fossil fuels

Fine particulate matter A complex mixture of very fine liquid droplets or solid particles in the air such as dust, smoke, and exhaust fumes. Smoke contains tiny carbon particles called soot. Haze is formed when smoke, dirt and particulate matter combine with water vapour in the air. When there is no wind, smoke may be trapped by fog to form smog Incomplete combustion of fossil fuels for example bonfires, open burning, the burning of oil wells and the burning of dried paddy stocks. Motorised vehicles (exhaust fumes) Quarries, sawmills and asbestos factoriesHealth: Irritate the eyes, nose and lungs Haze can cause conjunctivitis, sore throats, influenza, asthma and lead to bronchitis Dust from quarries, sawmills and asbestos factories can cause lung disease Haze leads to reduces visibilityAgriculture: Smoke particles(soot) deposit on leaves and block stomata. This prevents gaseous exchange Both lower the photosynthesis rate of plants which subsequently reduces crop yields.Climate: Contributes to the formation of haze and smog Smoke and haze can reduce visibilityBuildings: Soot darkens buildings

Air pollutant index The air quality is measured by the air pollutant index (API). This index is calculated based on the concentrations of several major air pollutants. Air pollution levels are divided into 5 bands as shown below:APIDescriptor

0 - 50Good

51 100Moderate

101 200Unhealthy

201 300Very unhealthy

>300Hazardous

Water pollution Water sources are the most easily polluted as they are the most affected by human activities. Industrial, domestic ad agricultural activities produce waste which pollutes water. The sources of water pollution are:1. Discharge of untreated sewage and domestic into rivers (faeces, rubbish and detergents) Encourage the growth of bacteria and cause diseases. Reduce the concentration of oxygen in the water due to the decomposition process The non-biodegradable rubbish prevents sunlight from reaching the aquatic plants, threatens life of aquatic plant.2. Discharge of industrial waste (organic waste from agriculture plantation, toxic chemical wastes from electronic factories) Decomposition of organic wastes reduce the concentration of oxygen in water. Non-biodegradable toxic chemicals accumulate in the body through the food chain. This can damage organs, cause cancer and mutation.3. Discharge of agricultural wastes (fertilisers, faeces) which contain nitrates and phosphates The high concentration of nitrates and phosphates in river or ponds cause eutrophication. Biochemical oxygen demand (BOD) increases4. Oil spillage Oil that spills from ships oil tanks can pollute the water and cause the death of aquatic animals in the sea It also pollutes the beaches.Eutrophication Eutrophication is the artificial nutrient enrichment of an aquatic system with organic material or inorganic nutrients, causing an excessive growth of aquatic plant life. Eutrophication can be caused by:a) The leaching of inorganic fertilisers, especially nitrates and phosphates, from agricultural landsb) The input of untreated sewage as well as discharge from sewage treatment plantsc) Run-offs containing animal wastes from pastures and farmlands into lakes, rivers or ponds.

Biochemical Oxygen Demand (BOD) Biochemical oxygen demand (BOD) is the amount of oxygen required by microorganisms to decompose the organic substances in the water. The dissolved oxygen concentration can be used as an indicator of water pollution level. A high BOD value indicates the presence of a large number of microorganisms and this suggests a high level of pollution.

The process and consequences of eutrophication1) Draining of excess nutrients into ponds, lakes and rivers encourages the rapid growth of photosynthesizing organisms especially algae. this results in a population explosion known as an algal bloom.2) The excessive growth of algae restricts the penetration of light into the water. As a result, the photosynthesis of other aquatic plants is greatly reduced and this further decreases the supply of oxygen in the water3) The algae also grow faster than their consumers, As a result, most of the algae die without being consumed.

4) As the photosynthesis organisms die and organic material accumulates at the bottom of the lake, decomposing microorganisms, especially aerobic bacteria, grow rapidly and use up oxygen in the deeper water at a fast rate.5) The aerobic bacteria uses up oxygen faster than it can be replenished. An increase in the BOD causes the oxygen levels to decrease rapidly.

6) The low level of oxygen concentration kills larger aerobic aquatic organisms such as fish. Organisms that require higher oxygen levels (for example, freshwater shrimps and mayfly nymphs) will not survive7) In extreme cases if the oxygen levels continue to drop and the water becomes completely deoxygenated, anaerobic bacteria will grow and release toxic gases such as hydrogen sulphide, causing the death of many aquatic organisms .

Thermal pollution In thermal pollution, the temperature of a body of water is unintentionally raised as a result of human activities.Causes of thermal pollution

1. Hot water is discharged into nearby lakes and rivers from the effluents of industrial processes and the cooling towers of electrical power stations which use water as a cooling agents.2. The excess heat that is released into the environment leads to thermal pollution.3. Thermal pollution causes the temperature in the body of water to rise above the normal value. The increase In temperature can be between 5 and 10 degree celcius

Effects of thermal pollution

1. Water temperature can affect the level of dissolved oxygen. When the temperature of water increases, oxygen become less soluble in water.2. a) For some species, a sudden increase in temperature can lead to instant death because many aquatic species can only survive within a certain range of temperature.b) The death of these species may have a negative effect on the food chain, causing the entire ecosystem to collapse3. For other species, for example, algae an increase in temperature actually encourages their rapid growth which lead to a higher BOD value4. If the temperature increase continues over a long period, this may result in permanent changes in the species composition of the aquatic ecosystem.

Ways to prevent thermal pollution

1. Control the amount of hot water discharged from industrial plants and power stations into the surrounding lakes and rivers.2. Control the amount of hot water or industrial effluents discharged into still or slow- moving rivers.

Noise pollution Noise from cars, motorcycles, aeroplanes, construction site, agricultural and industrial machinery can be form of pollution. The noise level of residential areas should not exceed 55 decibels (dB). According to the World Health Organisation (WHO), prolonged exposure to noise levels at or above 80 decibels (dB) can lead to deafness. Excess exposure to high levels of noise is considered a health risk because noise can contribute to stress-related problems such as high blood pressure, coronary disease, ulcers, depression and headaches.

9.2 The Greenhouse Effect and the Thinning of the Ozone Layer The greenhouse effect The greenhouse effect is an effect in the atmosphere as a result of the presence of certain gases, called the greenhouse gases. Greenhouse gases in the atmosphere are similar to the glass planes of a greenhouse which trap the heat and warm the greenhouse. Carbon dioxide, chlorofluorocarbon (CFC), methane, nitrous oxide, low level ozone, and water vapour make up the greenhouse gases. With the exception of CFC, most of the greenhouse gases occur naturally. However all of them are also the results of human activities. Today, data collected around the world show a steady increase in the concentration of greenhouse gases. At the same time, there is also rapid development and industrialization. Since the beginning of the Industrial Revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, the concentrations of methane have more than doubled, and the concentrations of nitrous oxide have risen by about 15%. Scientists believe that the combustion of fossil fuels (coal, petroleum and natural gas) and other human activities such as increased deforestation and industrial production are the primary reason for the increased concentrations of atmospheric carbon dioxide. As the concentrations of greenhouse gases increase, the greenhouse effect increase,trapping more heat in the atmosphere and raising the average temperature on earth. This overall rise in the average temperature of atmosphere is known as global warming.

The effects of global warmingOccurrence of floodsClimate changes

As the mean temperature rises, the polar ice caps and glaciers melt.A rise in sea levels causes low-lying areas to be floodedGlobal warming leads to changes in wind direction and the distribution of rainfall. As a result, agricultural activities are affected.Global warming causes weather patterns to change. This affects the distribution of species which may lead to the extinction of species in certain regions.

Occurrence of droughtSpread of diseases

Global warming increases the frequency of droughts.The land becomes dry and infertile.This leads to a drop in crop yields.With warmer climates, pests and vectors may spread to new areas.The warmer conditions lead to an expansion of territories for disease-carrying vectors, resulting in an increase in the outbreaks of diseases such as malaria, and dengue fever.

The thinning of the ozone layer Ozone layer is a region in the stratosphere which contains high concentrations of ozone molecules that absorbs ultraviolet (UV) radiation and shield organisms from its damaging effects.

Causes of ozone depletionThe effects of ozone depletion

1. The destruction of the ozone layer is mainly due to the increasing levels of chlorofluorocarbon (CFC) in the atmosphere.2. CFCs are very active chemicals that contain chlorine, carbon and fluorine.3. CFCs are used as coolants in air conditioners and refrigerators, propellants in aerosol cans and foaming agents in the making of Styrofoam packaging.4. CFCs are extremely stable and can remain in the environment for as long as 75 to 100 years.5. Once in the stratosphere, CFCs are broken down by UV rays.6. As a result the highly reactive chlorine radicals are released.7. These chlorine radicals break down the ozone molecules in a chain reaction1. Prolonged exposure to UV radiation can lead to higher risks of Skin cancer, such as melanoma. UV radiation causes mutations that can lead to skin cancer. Cataracts Sunburns2. UV radiation weakens the immune system and the ability of the body to resist infectious diseases.3. UV radiation reduces nutrient contents and crop yields of plants such as soya beans and peas.4. Leaf cells and chlorophyll are easily damaged by the UV rays. This lowers the rate of photosynthesis and reduces crop yields.5. Ozone depletion also leads to an increase in the temperature on Earth.

Process of ozone depletion by CFCa) UV rays break down the CFC molecules in the atmosphere. A chlorine atom is released.

b) The highly reactive chlorine atom breaks down the ozone molecule into chlorine monoxide and oxygen molecule

c) Free oxygen atoms in the atmosphere break the chlorine monoxide bond. A chlorine atom is released and it can destroy more ozone molecules.

9.3 The importance of proper management on the development of activities and the ecosystemThe need for development and the effects of an increasing population the ecosystem As the population of the world increases, so do the needs of this population. The needs for more food supplies, water, homes, hospitals, transport system has led to deforestation, the burning of fossil fuels, the building of more dams and the production of more domestic and industrial waste. The drive for development and the attempt to raise the standard of living have led to many economic activities and development projects. These activities and development projects have led to frequent human interference with the balance of nature. The negative effects of hasty, unplanned ad unmanaged development are various environmental problems. This environmental problems affect our health, the management of resources and the ecosystem. There is a conflict between the need to meet the requirements of an increasing population and the need to deal with the growing environmental problems. Every economic activity or development project must be balanced by efforts to manage the environment in a sustainable manner.Measures taken in the management of development activities Implementation of lawsMany laws and regulations are designed to control pollution which affects the quality of land, air and water. Below are some of the acts:a) the Environmental Quality Act, 1974, 1989b) the National Forestry Act, 1984c) the Protection of Wildlife Act, 1972

Use of technologya) Install catalytic converters in vehicles to clean up exhaust emissions and convert the harmful gases released during the combustion of fossil fuels to less harmful productsb) Use unleaded petrol to reduce the emission of lead into the environmentc) Treat sewage in sewage treatment plants before it is discharged to reduce water pollutiond) Usage of oil-disintegration bacteria to clean up oil spillage in the sea.e) Install factory chimneys with specific devices to filter fine particles.f) Develop hydrogen-based fuel-cell vehicles

Education on the management of resourcesThe public must be educated on the concept of 4Rs. The 4Rs stand for recycle, reuse, reduce and recover.a) Recycling means collecting and segregating waste according to the types of materials and turning this waste into new products.b) Reuse means use things such as old plastic containers and bottles again for other purposes instead of throwing them away.c) Reduce means cutting down on the use of materials.d) Recover means to harness heat energy from the burning of materials or refuse in factories or incineration plants. This heat energy can be used to generate electricity.

Preservation and conservation of soil, water, the flora and fauna of forests, and mangrove swamps1. Conservation involves efforts to return an affected ecosystem to its natural equilibrium.2. Sustainable agricultural development is the effective use and preservation of soil to Preservation involves effort to protect an ecosystem so that natural resources are utilized in a sustainable manner and that the equilibrium of the ecosystem is maintained.3. ensure continuous agricultural production.a) Good farming techniques will prevent erosion and soil depletion.b) Good agricultural practices include crop rotation, contour farming, controlled grazing, planting cover crops, the appropriate use of fertilisers, and effective drainage and irrigation.4. Clean water is a precious resource. As such, water resources and water catchment areas must be preserved.a) Rivers must not be regarded as dumping sites for domestic and toxic wastes which can pollute the water.b) The use of nitrates and phosphates in agriculture must be controlled5. Sustainable and planned forests projects:a) Establishment of a level of selective harvesting.b) Reforestation or large-scale replanting of trees. c) Implementation of restoration programmes to restore damage habitats.d) Establishment of forest reserves.6. Mangrove swamps are a rich source of biodiversity. Mangrove swamps play an important role in flood control, nutrient retention, sediment control, and the prevention of coastal erosion. Mangrove swamps found along the coastlines must be protected, preserved and conserved. The practice of biological control1. Biological control is the use of natural predators to control the population of pest species.2. This method involves the prey-predator relationship. The predators do not harm the crops.3. Biological control is better than chemical control which involves the use of pesticides. This is because:a) The use of pesticides is indiscriminate and sometimes harmless organism as well as the pest species are killed.b) The effects of pesticides can be persistent and remain in the environment for long periods.c) The concentration of pesticides is amplified as they pass through food chains (bio-magnification). As a result, high concentrations of pesticides may accumulate in the tissues of final consumers.d) Pest develop resistance.e) the cost of using pesticides is high.f) Pesticides pollute the environment.

The use of renewable energy1. Renewable energy is inexhaustible and does not pollute the environment.2. Examples of renewable energy are:a) Solar energyb) Wind energyc) Wave energyd) Geothermal energye) Biomass energyf) Gasoholg) Palm oil fuel3. Renewable energy can be used as an alternative source of energy to fossil fuel which is a non-renewable energy.

The efficient use of energy1. Reduce the burning of coal, petroleum and other fossil fuels.2. Substitute natural gas for coal at power plants.3. Improve fuel efficiency in vehicles-use cars that run on energy-efficient engines.4. Use a cleaner fuel by reducing the content of sulphur in diesel and switching to gas.5. Improve energy efficiency in factories.6. Use more hybrid cars which combine electric and gasoline engines.CONTENT

1. Human activities that endanger an ecosystem Human activities that threaten an ecosystem The impact of human activities on the ecosystem Pollution

2. The greenhouse effect and thinning of the ozone layer The greenhouse effect The thinning of ozone layer

3. The importance of proper management of development activities and the ecosystem The need for development and the effects of an increasing population on the ecosystem Measures taken in the management of development activities.