B3.4 Human Impact on the Enviroment

Humans reduce the amount of land available to other animals and plants by:

• Farming - Large areas of land are used to provide food for humans. Creating these large fields destroys hedgerows, the habitat for many small animals. Often only one type of crop is grown, limiting the area of land for growth of other types of plant
• Building - Humans use the land to build for example houses, schools, offices and factories
• Quarrying - Humans need materials such as stone to build with. They will dig these substances from the land and create areas of land that cannot support animal or plant life while the land is being excavated
• Dumping Waste - Tips take up a large area of land and humans are constantly adding to waste sites

Raw materials, including non-renewable energy resources, are being rapidly used up:

• non-renewable energy resources, such as coal, oil and natural gas, are being used up rapidly
• raw materials are being used up rapidly
• more waste is being produced, more pollution is being caused

More waste is being produced which, unless properly handled, may pollute: 

• Sewage - eutrophication --> fertilisers from farms leach into water nearby, algae grow rapidly, bacterial growth(decay), bacteria use Oxygen for respiration = less oxygen in water = death of aquatic organisms
• Human Waste - from the growing population
• Pollutant Gases - less trees to absorb CO2 and CO2 causes global warming. SO4 causes acid rain (produced in power stations)

People pollute land in many different ways:

• Sewage contains human body waste & waste water from our homes. Sewage must be treated properly to remove gut parasites & toxic products or these can get onto the land
• Large quantities of household & industrial waste are placed in landfill & toxic chemicals leak out. Some industrial waste, such as, radioactive waste, is very hazardous
• Farming methods can pollute the land: Herbicides (weedkillers) & pesticides (which kill insects) are also poisons. The poisons sprayed onto crops can get into the soil & into the food chain. Eventually many of them are washed into rivers. Farmers use chemical fertilisers, to keep the soil fertile, which can be washed into rivers

Water pollution:

• Herbicides, pesticides & chemical fertilisers all get washed into rivers and streams
• Fertilisers and untreated sewage can cause a high level of nitrates in water
• Toxic chemicals from landfill leak into waterways, polluting & killing organisms such as fish

Burning fuels can produce sulphur dioxide and other acidic gases. Power stations and cars release acidic gases. The sulphur dioxide dissolves in water in the air, forming acidic solutions. The solutions then fall as acid rain - sometimes a long way from where the gases were produced. Acid rain kills organisms. Trees can be damaged if the leaves are soaked in acid rain for long periods.

Acid rain can change the soil pH, which damages roots and may release toxic minerals. For example, aluminium ions are released which also damages organisms in the soil and in waterways.

Enzymes, which control reactions, are very sensitive to pH (acidity or alkalinity). When trees are damaged, food and habitats for many other organisms are lost.

Deforestation is the destruction or removal of areas of forest/woodland.

Reasons for deforestation are to clear land for farming, to use the trees for fuel and to produce more food through farming.
There has been a lot of deforestation in tropical area due to the need for more land for crops for the increasing human population. The effects of large scale deforestation are:

• lose of biodiversity as many species of animals/plants die out
• destroying new sources of food/medicine for future
• when forests cleared they are often replaced by a monoculture (single species) reducing biodiversity

Deforestation reduces biodiversity as it wipes out species and replaces with a single species. The effect of having many cattle being reared is a lot of methane in being produced which affects global warming. 

Peat bogs are made of plant material that can't decay completely because of acidic conditions and lack of oxygen. Peat bogs are stores of carbon so as it is burned as fuel, CO2 in air increases and carbon storage decreases.

Levels of carbon dioxide and methane are increasing in the atmosphere. They are called greenhouse gases and cause the greenhouse effect. Most scientists believe an increase in greenhouse gases contributes to global warming.
An increase in Earth's temperature of only a few degrees Celsius may:

• Cause big changes in the Earth's climate
• Cause a rise in sea level due to melting of ice caps and glaciers
• Reduce biodiversity
• Cause changes in migration patterns e.g. of birds
• Result in changes in the distribution of species

Biofuel is made from using living organisms or the waste that they produce.

Biogas - produced from the breakdown of organic matter

Ethanol - produced by the fermentation of sugar from plant material

Biofuel is renewable, gets rid of waste and is carbon neutral.

Produced by anaerobic fermentation of organic waste containing carbohydrase by bacteria. This gas contains:

• 40-70% methane
• CO2
• traces of hydrogen and hydrogen sulphide

Currently used in production of electricity, heating water for central heating system and as fuel for buses.

On a large scale we use a digester. The carbohydrase-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. The optimum temperature would be 32-35 degrees Celsius.

They have a continuous flow method where we add organic material and remove remaining solids at a constant rate.
Biogas is ideal in remote areas.

Produced by anaerobically fermentation of glucose by yeast is used to make fuels such as gasohol.

It is successfully used to fuel cars.

Gasohol normally contains 10% ethanol and 90% petrol so still produces CO2. This allows gasohol to be used in unmodified engines.

• Glucose obtained from maize or sugar cane
  • broken down into glucose by carbohydrase
• Yeast added to the glucose, they respire anaerobically producing ethanol and CO2
• Pure ethanol is obtained by distilling the mixture

Intensive farming - getting the maximum increase in biomass from animals without feeding them extra.

• Methods
  • Limit their movement - they don't use much energy in moving their muscles and so have more biomass available from food growth
  • Controlling the temperature of their surroundings - don't use as much energy keeping warm/cooling down. Leaves more biomass spare for growth

Sustainable food production means producing food in a way which can continue for many years. An example which how fish stocks are managed. 

• Net Size (nets with large mesh used) - only biggest fish caught and so young fish are caught
• Fishing Quotas - breeding season is banned from fishing

The fungus Fusarium to grown to produce mycoprotein. This is a protein-rich food suitable for vegetarians. Fusarium is grown aerobically on cheap sugar syrup made from waste starch and the mycoprotein harvested.

Microorganisms can be grown on a large scale in industrial fermenters. The conditions in a fermenter must be controlled to ensure maximum growth of the Fusarium. 

Industrial fermenters are large vessels which have:

• an air supply providing oxygen for respiration
• stirrers or gas bubble used to keep the microorganisms spread out and to provide an even temperature
• a water-cooled jacket around the outside, as the respiring microorganisms release energy which heats the contents
• sensors to monitor both pH and temperature

Must control pH, temperature and oxygen levels.

There are many human activities which can affect the global environment. These include:

• deforestation which can cause increased levels of carbon dioxide in the atmosphere
• increases in rice growing and rearing cattle resulting in more methane being released
• building dams, to store water in reservoirs, causing loss of habitats, drying out of rivers below dams and reduction in fertile land to grow crops

There are huge amounts of environmental data produced by many different scientists in many different countries. It can be very difficult to be sure the data are valid and reliable.

Scientists often come to different conclusions even when considering the same data. Explanations sometimes depend on the individual opinion of the scientist and can be biased.

The issue of global warming divides opinion. Many people think the Earth's temperature has increased due to increases in greenhouse gases. Others say the increase is part of a natural cycle.