Waste from human activity
The rapid increase in the human population and improvements in living standards during recent years have resulted in an increased demand for land, energy and resources. It has also lead to greater quantities of waste being generated, which, in turn, has led to the pollution of land, water and air. This pollution has changed the environment in many eco-systems, making it harder for many species to survive.
waste from human activity 2
Like all living things, humans exploit their surroundings for resources. Before the beginning of agriculture - around 10,000 years ago - small groups of humans wandered across large areas, hunting and gathering just enough food to stay alive. Population numbers were kept low because of the difficulty of finding food.
Over time, the development of agriculture led to increases in population around the world. But it was not until the 20th century that population numbers began to explode, and this steep rise was accelerated by huge improvements in hygiene and healthcare.
Waste from human activity 3
Standards of living; In addition to the huge rise in population, there has been a big rise in the standard of living standard of living, especially in the developed world. People in the developed world now enjoy a high standard of living - with abundant food, cars and comfortable housing. People in the developing world have a lower standard of living, but many countries are catching up quickly.
Impact of humans; The growth in the human population and the improvements in the standard of living are putting strains on the global environment. Here are some of the ways in which this is happening:
Non-renewable energy resources (such as coal, oil and natural gas) are being used up rapidly.
Raw materials are being used up rapidly.
More land is being used for buildings and transport networks, quarrying, farming and dumping waste - reducing the amount of land available to other animals and plants.
More waste is being produced - causing more pollution.
Waste from human activity 4
Land and water pollution
Pollution is the addition of substances to the environment that may be harmful to living organisms . Population growth and a higher standard of living cause more waste to be produced. If this waste is not handled correctly, it leads to pollution.
In order to improve the yield from their land, most farmers spray their crops with chemicals including herbicides and pesticides. Herbicides increase crop yield by killing or inhibiting the growth of weeds, reducing the competition for resources such as minerals, space and sunlight. Pesticides increase yield by killing off pests, such as small insects or plant pathogens, which would otherwise feed on or damage the crops. However, some of these chemicals can remain in the soil for long periods, polluting the land, and they may also be washed into rivers, lakes and seas. There can also be consequences further up food chains within an eco-system- with pollution disrupting food chains or accumulating to toxic levels. Most rubbish is buried in landfill sites and some of it may be unsafe. Even common household items can contain toxic chemicals such as poisonous metals. Industrial waste is also discharged onto the land.
Waste from human activity 5
Water pollution is caused by the discharge of harmful substances into rivers, lakes and seas.
Fertilisers are used by farmers to increase their crop yield, supplying extra minerals to their plants so they grow better. However, these minerals can run off into waterways and lead to a process called eutrophication. This involves the over-growth of algae and ultimately leads to oxygen depletion from the water and the death of invertebrates and fish. This causes food chains within the eco-system to collapse.
Sewage may also pollute waterways. Sewage contains high mineral levels and can promote the process of eutrophication (see above). It may also contain harmful pathogens.
Toxic chemicals from industries and mining can also pollute waterways. These chemicals might be highly toxic, or might accumulate in food chains to toxic levels.
Waste from human activity 6
The most common source of air pollution is the combustion of fossil fuels. This usually happens in vehicle engines and power stations. However, there are other sources of atmospheric pollution (see table below).
Common air pullutants
Air pollutant Source Typical effect Smoke Incomplete combustion of fossil fuels, especially coal. Deposits soot on buildings and trees, causing them damage. Permeates the air - which can cause breathing problems in living creatures. Sulfur dioxide Combustion of fossil fuels with sulfur impurities in them, eg coal. Contributes to acid rain. This can cause weathering of buildings, the release of toxic metals from the soil, damage to aquatic ecosystems and to forests. Carbon dioxide Combustion of hydrocarbon fuels. Greenhouse gas that contributes to global warming . Methane Rice fields, cows, anaerobic decomposition of landfill waste. Greenhouse gas that contributes to global warming.
Deforestation and the destruction of areas of peat
The growth of the human population has created a greater demand for food, energy sources, natural resources and land. New land is increasingly being found by cutting down rainforests, allowing agriculture to expand. But this has negative consequences for both the environment and for biodiversity. This exploitation of natural resources is also occurring with peat bogs - again with negative consequences.
Deforestation and the destruction of areas of peat
The world’s forests, especially rainforests, are vital in that they provide unique habitats for many unique species. They also act as a ‘carbon sink’, trapping away lots of carbon in their biomass that was previously absorbed for photosynthesis.
Humans have been cutting down trees for thousands of years. However, this clearing of forests has accelerated in recent decades and is now being carried out on a large scale. This is known as deforestation. The reasons for deforestation:
To provide timber as a fuel or a building material.
To provide extra land for agriculture. This agricultural land is often used to grow rice in paddy fields or to rear cattle in order to satisfy the increasing demand for food. However, increasingly this land is being used to grow crops for biofuel production (based around bioethanol ) in order to satisfy the increasing demand for energy.
Deforestation and the destruction of areas of peat
Consequences of deforestation
Deforestation has some important consequences:
It reduces the rate at which carbon dioxide is absorbed and ‘locked away’ in the plant biomass by photosynthesis, as there are fewer trees.
As timber is burnt to clear space, it increases the release of carbon dioxide into the atmosphere. The remaining parts of the tree (eg the roots) are then decomposed by microorganisms. This adds further carbon dioxide to the atmosphere and so contributes to global warming.
Forest habitats are destroyed and biodiversity is reduced.
Rice fields - created to satisfy the need for food production due to the growing population - are grown on previously deforested land and also produce methane when the crop rots.
Deforestation and the destruction of areas of peat
The term biodiversity refers not only to the number of different species. It also refers to all the variations within and between species, and all the differences between the habitats and ecosystems that make up the Earth’s biosphere.
The loss of forests reduces biodiversity and we run the risk of losing organisms that might have been useful in the future - for example, as sources of new medicines. There is also a moral responsibility to look after the planet and its resources.
Deforestation and the destruction of areas of peat
Destruction of peat bogs
What is peat?
Peat is formed in waterlogged, acidic fens and bogs over thousands of years by the growth of mosses and other plants, which absorb and ‘lock away’ carbon dioxide during photosynthesis. When the moss dies, the waterlogged bog provides anaerobic conditions which, together with the acidity of the bog, prevent the total decomposition of the moss. It accumulates in the bogs in a partially-decomposed state, forming peat.
Deforestation and the destructuion of areas of pea
The importance of peat
Peat bogs cover nearly 2-3% of the Earth’s surface and are an important carbon sink,containing more ‘locked-away’ carbon than the Earth’s forests.
However, the amount of biomass it contains means it can be dried and burnt as a fuel, which makes it an important energy source in some countries. Peat also has valuable properties when mixed in with soil - including improved soil structure, mineral retention, water retention and acidity - making it valuable in agriculture and gardening. Many peat bogs have been drained to allow the peat to be extracted. However, the use of peat causes problems. Burning the peat releases its stored carbon back into the atmosphere as carbon dioxide. Similarly, as peat is mixed in with soil it is exposed to aerobic conditions and begins to decompose - which again causes the release of its trapped carbon as carbon dioxide. This is in addition to the carbon dioxide released in extracting the peat. Therefore, the destruction of peat bogs contributes to global warming as well as destroying important habitats.
Deforestation and the destruction of areas of peat
Consequences for gardeners
Since the 1950s, many gardeners have bought peat-based composts due to their perceived benefits (see above).
However, the impact of peat extraction in terms of global warming and habitat destruction has seen a rise in the number of gardeners opting for ‘peat-free’ composts which contain sustainable alternatives to the use of peat. This trend has been supported by government targets for reducing the use of peat in compost.
The rising demands for energy from a growing population have led to the burning of increasing amounts of fossil fuels, which generate carbon dioxide emissions. These emissions, along with other greenhouse gas emissions, are leading to global warming - which is predicted to have very serious consequences for the environment in the coming decades. Fossil fuels are also non-renewable. An alternative to fossil fuels, which is being investigated, is the use of biofuels.
The presence of certain greenhouse gases in our atmosphere naturally results in the Earth being warmer than it should be, as the gases trap some of the Sun’s heat and prevent it escaping from our atmosphere. This is called the greenhouse effect.
Global warming is the term which is used to describe the increase in the Earth’s temperature above the natural greenhouse effect. This increase is caused by additional greenhouse gases being released.
The two main greenhouse gases which are increasing in the atmosphere are carbon dioxide and methane.
Why are greenhouse gas levels increasing?
Carbon dioxide levels are increasing because:
Humans are burning more fossil fuels to provide energy.
Humans are cutting down forests - reducing the number of trees that can absorb carbon dioxide.
Humans are destroying peat bogs – and the process of destroying them releases carbon dioxide.
Methane levels are increasing because:
Humans are rearing more cattle to supply food. During their digestive process, cows produce a lot of methane.
Humans are planting more rice paddy fields to supply food. These grow in water, creating anaerobic conditions - and therefore as plants rot, methane is produced.
Humans are producing more waste - which produces methane as it decays anaerobically.
Why do greenhouse gases cause global warming?
- Heat from the Sun enters the Earth’s atmosphere and warms the Earth’s surface.
The Earth’s surface becomes hotter and radiates heat back out.
Some of this heat is absorbed by greenhouse gases. These gases then radiate the heat back towards Earth.
The Earth becomes warmer as a result.
Consequences of global warming
A major area of uncertainty is what will happen over the next century as greenhouse gas levels in the atmosphere continue to rise. Computer models indicate that the temperature will rise - but different models generate slightly different values for this temperature, as assumptions about the future vary slightly. However, a rise of only a few degrees Celsius may:
cause big changes in the Earth’s climate and weather patterns
cause ice caps on land to melt causing a rise in sea level - resulting in flooding and low lying areas being submerged
cause changes in the migration patterns of birds and other organisms
result in changes to the distribution of species (ie where they are found) as some species move to cooler areas to cope with the increase in global temperatures
Carbon dioxide sequestering
The oceans, lakes and ponds of planet Earth are important as they absorb and ‘lock away’ over a quarter of the carbon dioxide that humans emit into the atmosphere. The process by which they absorb and lock away the carbon dioxide is known as sequestration. This occurs due to:
Carbon dioxide being soluble and dissolving directly in the water.
This sequestering plays an important role in removing carbon dioxide from the atmosphere. As carbon dioxide levels in the atmosphere rise, it is likely that more would be sequestered in the oceans, rivers and ponds.
Many organisations and companies are also looking at how more carbon dioxide can be sequestered by enhancing natural sequestration (eg getting the phytoplankton to do more photosynthesis) or by using artificial sequestration.
With fossil fuels being non-renewable and contributing to global warming, biofuels are increasingly considered to be a possible alternative for the future. Biofuels are produced from natural products, often plant biomass containing carbohydrate. As biofuels are produced from plants, they are renewable and theoretically carbon neutral.
Some biofuels are produced by using microorganismsto anaerobically ferment carbohydrate in the plant material, as is the case with bioethanol and biogas production (each process uses different microorganisms).
Ethanol is the type of alcohol found in alcoholic drinks such as wine and beer. It is also useful as a fuel. It is usually mixed with petrol for use in cars and other vehicles.Ethanol can be made by a process called fermentation. This converts sugar into ethanol and carbon dioxide if conditions are anaerobic. Single-celled fungi, called yeast, contain enzymes that are natural catalysts for making this process happen:
In some countries, eg Brazil, the source of sugar is sugar cane - which yeast can directly ferment into ethanol. In other countries, plants such as maize are used. Because maize contains starch rather than sugar, the enzyme amylase must first break down the starch into sugar before the yeast can ferment it into ethanol. The ethanol produced by yeast only reaches a concentration of around 15 per cent before the ethanol becomes toxic to the yeast. In order to make it sufficiently concentrated to be burnt as a fuel, the ethanol must be distilled.
Disadvantages of bioethanol
There are some disadvantages to growing biofuel crops, such as sugar cane and maize, to be used as bioethanol:
The demand for biofuel crops means greater demand on rainforest land.
Crops grow slowly in parts of the world that have lower light levels and temperatures, so growing biofuel crops in these countries would not satisfy the demand for fuel.
For bioethanol to be burnt in a car engine, some engine modification is needed. Modern petrol engines can use petrol containing up to 10 per cent ethanol without needing any modifications, and most petrol sold in the UK contains ethanol
Although biofuels are in theory carbon neutral, this does not take into account the carbon dioxide emissions associated with growing, harvesting and transporting the crops, or producing the ethanol from them. Therefore, overall, more carbon dioxide is emitted than is absorbed - which means that it contributes to global warming.
Some people morally object to using food crops to produce fuels. For example, it could cause food shortages or increases in food prices.
It is mainly composed of methane, with some carbon dioxide and other trace gases. However, the proportion of methane within the biogas can vary between 50% and 80%, depending on whether some oxygen is able to enter at the beginning or during the process. If some oxygen is present, the bacteria will respire aerobically and will produce a gas with a higher proportion of carbon dioxide and a lower proportion of methane.
Biogas can be produced on a small scale in a biogas generator/digester, which can be made of simple materials.
The carbohydrate-containing materials are fed in, and a range of bacteria anaerobically ferment the carbohydrate into biogas. The remaining solids settle to the base of the digester and can be run off to be used as fertiliser for the land. These types of biogas generator are most commonly used in the developing world to satisfy the needs of a small family.
The optimum temperature for biogas production is between 32oC and 35oC. Temperatures above and below this optimum can result in less biogas being produced, which can be a problem in hotter and cooler countries (see table below).
CountryProblemSolution Cooler country (eg UK) Temperatures below optimum slow the respiration rate of bacteria resulting in slower biogas production. Bury the biogas generator or build the biogas generator with thick walls to insulate the generator and keep the inside warmer than the external temperature. Hotter country (eg India)
Temperatures above optimum begin to denature bacterial enzymes, resulting in slower biogas production.
Bury the biogas generator in the ground. The ground helps to insulate the biogas generator to keep it cool during the day and warm at night.
If a bigger, more sophisticated biogas generator is used, biogas can also be produced on a large scale.
Biogas is naturally produced in landfill sites as bacteria anaerobically break down our rubbish, but normally the methane escapes into the atmosphere where it contributes to global warming. If a pipe network with holes in it can be built into the landfill site - and the methane is prevented from escaping into the atmosphere by covering the site - then the methane can be collected via the pipe network.
The methane can then be used as a fuel to generate electricity or heat buildings, eg care homes, hospitals and schools. This is an example of biogas generation on a commercial scale.
A growing population brings with it a necessity to produce more food. However, the potential impact on the local and global environment must be considered. Part of the solution lies in careful management to reduce energy losses in food chains, as well as looking to new food sources. It is necessary to find a compromise between the priority of obtaining food and the priority of protecting ecosystems.
Food production 2
Efficiency of food production
Both biomass and the energy within it decrease up a food chain. At each level in the chain, energy/biomass is lost through waste (eg faeces) or through respiration and associated processes (such as movement and maintaining body temperature).The efficiency of food production can be improved by reducing the number of levels in the food chain. This is because fewer energy losses occur along a shorter food chain, meaning a greater proportion of the energy that entered the food chain is available to humans and more people can be fed.
The efficiency of food production from animals can be improved by reducing the amount of energy lost to the surroundings. This can be done by:
Preventing animals moving around too much - this conserves energy which can be used to increase biomass.
Keeping their surroundings warm - this preserves the energy which would have been used to maintain their body temperature, so that it can be used to increase biomass.
Foos production 3
The main advantages for keeping animals in warm sheds with little space to move are that it results in more efficient food production - and therefore cheaper food. However, there are disadvantages in terms of reduced animal welfare, increased risk of injury, and increased risk of diseases (eg salmonella amongst chickens).
A balance must be reached between the needs of farmers and consumers and the welfare of the animals.
Food production 4
Calculating energy efficiency
This bullock has eaten 100 kJ of stored energy in the form of grass, and excreted 63 kJ in the form of faeces, urine and gas. The energy stored in its body tissues is 4 kJ. So how much has been used up in respiration?
The energy released by respiration
= 100 - 63 - 4 = 33 kJ
Only 4 kJ of the original energy available to the bullock is available to the next stage in the food chain, which might be humans.
The efficiency of this energy transfer is:
4/100 × 100 = 4%
Food production 5
The increasing demand for food, especially protein-based food, to feed the growing world population has also led scientists to investigate alternative ways of obtaining food from microorganisms.
Mycoprotein is a high-protein food produced from the fungal biomass of a soil fungus called Fusarium . It also has a high fibre content, and is low in fat with no cholesterol. This makes it a healthy, vegetarian alternative to meat.
Mycoprotein is grown in a fermenter - an apparatus for growing cultures on a large scale.
The fermenter is aseptically filled with a sterile broth containing glucose syrup, obtained from the breakdown of plant starch by amylase enzymes. To this is added a small starter culture of the Fusarium fungus.
Sterile glucose syrup, ammonia and air (containing oxygen) are then added continuously for a period of six weeks, so that the fungus has the correct nutrients and conditions to grow.
Food production 6
The role of the ammonia is to provide a nitrogen source for the fungus to produce amino acids - the building blocks of protein - while the air ensures that the conditions in the fermenter are aerobic as well as mixing the broth to ensure it is uniform throughout.
During the six-week period, the fungus and grows, doubling its biomass every five hours. The cooling coils remove the excess heat generated by the fungus during respiration, keeping the temperature inside the fermenter constant at its optimum level.
At the end of the six-week period, the fungal biomass is harvested and purified by heating it to 65oC to remove harmful substances, and spinning it dry using a centrifuge. The yellow solid substance which is obtained can then be flavoured and shaped into different products.
Food production 7
Fish are an important part of the human diet, accounting for a worldwide average of 15 per cent of protein intake. Most of these fish are caught wild.
As the population has increased, so has the demand for fish. If fish are caught at a faster rate than the remaining fish can reproduce, the numbers of fish – the fish stock – will decline. Trying to harvest more fish than the sea can produce is an example of unsustainability. North Sea cod have been overfished since the 1960s. Increasing numbers of boats - using increasingly sophisticated technology - were able to catch more and more cod. At first, catches continued to rise each year. However, the size of catches then started to decline as cod populations fell, leaving fewer and fewer breeding fish to maintain cod numbers.
Food production 8
In order to prevent the disappearance of certain fish species in some areas, it is important to maintain fish stocks at a level that allows breeding to occur and ensures that fish populations remain at a sustainable level. As a result of the near collapse of some fish populations, the European Union introduced regulations to conserve fish stocks.
These regulations included:
Setting fishing quotas for EU countries and for individual fishing vessels, which limited the amount of each species of fish which could be caught. By catching fewer fish, more are left to breed, so in time the population should recover.
Limiting mesh size of the nets. By increasing the size of the holes in nets, only mature, full-sized fish can be caught and immature fish can escape and eventually breed, allowing the population to recover.
In spite of these measures, stocks of cod and some other fish remain dangerously low.
Food production 9
Humans must also consider the impact of their food production on the environment. In order to supply cheap produce all year round, many supermarkets import food from other countries around the world - where it is cheaper to produce or grows more plentifully. Some developing countries rely on food exports to the UK to generate income.
The distance that food travels from the farm where it is produced to the consumer is referred to as ‘food miles’. Locally grown produce has far fewer food miles than produce grown in other countries.
The greater the distance the food has travelled, the greater the impact on the environment. This is due to the pollution from carbon dioxide emissions, generated by the transporting vehicles.
A compromise must be found between the monetary cost to the consumer, the impact on developing economies and the environmental cost of the pollution associated with transporting food over such long distances.