Please enable JavaScript.
Coggle requires JavaScript to display documents.
Human influences on the environment (Modern Agriculture (Pest control…
Human influences on the environment
Humans make increasing demands on the environment for:
Food to sustain an ever-increasing population
Materials to build homes, schools and industries
Fuel to heat homes and power vehicles
Space in which to build homes, schools and factories, as well as for leisure facilites
Space in which to dump our waste materials
Modern Agriculture
Crop plants depend on light and mineral ions from the soil as well as other factors in the environment. Stock animals depend on crop plants for food
FOOD WEB:
grass and root crops
cattle and sheep
humans
potatoes and other vegetables
wheat, barley, sugar beet and oilseed rape
poultry
manufactured products such as bread, breakfast cereals and margarine
Improving yields
Factor controlled
How it is controlled
Reason for controlling the factor
Soil ions
adding fertilisers,
growing in a hydroponic culture
extra mineral ions can be taken up and used to make proteins and other compounds for growth
Soil structure
ploughing fields to break up compacted soil,
adding manure to improve drainage and aeration of heavy clay soils
good aeration and drainage allow better uptake of mineral ions and water
Glasshouses and polytunnels
Can provide very controlled conditions for plants to grow
The transparent walls of the glasshouse allow enough natural light for photosynthesis during summer, and additional lighting gives a 'longer day' during winter
Greenhouse effect – heats the glasshouse up, reduces convection currents that would cool it
Can be heated to raise the temperature
Grown in a hydroponic culture » can provide exactly the right balance of mineral ions
Polytunnels are large tunnels made of transparent polythene
Fertilisers
Two main types: organic & inorganic
Many organic fertilisers (eg. manure) are made from animal faeces and straw
Inorganic fertilisers are just inorganic compounds, eg. potassium nitrate, ammonium nitrate
Carefully formulated to provide the specific amount of ions required
Manure returns some nitrogen to the soil but it is made from indigestible fodder and faeces so it can only replace a portion of lost nitrogen
Inorganic fertiliser is applied to replace the nitrates and other mineral ions
Can lead to pollution problems
:: organic fertilisers improve soil structure as they contain decaying matter and inorganic fertilisers do not
Another way:
Grow a legume crop (eg. clover) in a field one year in four
Legumes have nitrogen-fixing bacteria – convert nitrogen gas to ammonium ions
Some of this is passed to the plants
End of season – crops are ploughed into soil and decomposers convert the nitrogen in proteins to ammonia
This is then oxidised to nitrate and made available for next year's crop
Pest control
Pests – organisms that reduce the yield of crop plants or stock animals
Yield – the amount produced for sale
Pests can harm yield by:
lowering the amount by reducing growth (eg. damaging leaves » reduced photosynthesis)
affecting the appearance or quality and making it unsuitable for sale
Pests can be controlled using pesticides or by using biological control
Naming pesticides:
Herbicides – plant pests (weedkillers)
Insecticides – insects
Fungicides – fungi
Molluscicides – snails and slugs
Pesticides
Pest may develop resistance – natural selection
» existing pesticide is useless
Pesticides can cause environmental damage
Slow to decompose –
persistent
in the environment
Build up in the tissues of organisms –
bioaccumulation
Build up and become concentrated along food chains –
biomagnification
Kill other insects that are harmless as well as helpful species (eg. bees)
An ideal pesticide should:
control the pest effectively
be biodegradable » no toxic products are left in soil or crops
be specific » only the pest is killed
not accumulate in organisms
be safe to transport, store and apply
be easy to apply
Biological control
Uses another organism to reduce the numbers of a pest
Never fully gets rid of a pest because then the control organisms would have no food supply and die
Aims to reduce pest numbers to a level where they no longer causes significant economic damage
Methods:
introducing a natural predator
ladybirds control aphids in orange groves
introducing a herbivore
moth from S America controls prickly pear cactus in Australia
introducing a parasite
the wasp Encarsia controls whiteflies in glasshouse tomato crops
introducing a pathogenic microorganism
myxomatosis controls rabbits in Australia
introducing sterile males
mate with females but no offspring are produced so numbers fall
using pheromones
natural chemicals to attract mates used to attract pests to traps, destroying the pests
male-attracting pheromones control aphids in plum crops
Fish Farming
1/4 of farmed fish is used to make animal feed
Fish are kept in densely stocked tanks or enclosures in rivers or lakes, or in sea cages
Advantages:
Water quality can be monitored (eg. temp, O2 levels, water clarity and amount of chlorophyll) – large concentrations of chlorophyll give a warning of 'algal bloom'
Conditions can be modified (eg. air can be pumped into the enclosures to increase the amount of O2 dissolved in the water)
Water is pumped through filtration units to remove the waste products of the fish
Diet of the fish is carefully controlled in quality and frequency of feeding
Fish are protected against predators and pesticides are used to kill parasites
Selective breeding programmes can be used to improve quality of fish (eg. bred to produce faster growth and to be more placid than wild fish)
Criticisms:
Potential for spread of disease is greater than normal – animals closer together – antibiotics are used
» antibiotics used may not have degraded by the time fish are eaten by humans
» increases antibiotic resistance in bacteria
Pollution problems – organic material from faeces and food pellets contaminates the water outside the farm and leads to eutrophication
Pesticides used may be toxic to other non-harmful species of invertebrates
Has a negative effects on wild fish stocks
Carnivorous species are fed with pellets made from other fish
Need to eat several kgs of wild fish to make 1kg of farmed fish
Air pollution
Pollution is the contamination of the environment by harmful substances that are produced by the activities of humans
Carbon dioxide and global warming
CO2 levels have increasing by nearly 30% in the last 100 years, mainly due to the increased burning of fossil fuels
– eg. coal, oil, natural gas, and petrol and diesel in vehicles engines
– made worse by cutting down large areas of tropical rainforest
CO2 and other greenhouse gases contribute to global warming / the enhanced greenhouse effect
The normal greenhouse effect occurs naturally – without it more heat would be lost to space and surface temp would be 30° less
GGs include:
carbon dioxide
water vapour
methane
nitrous oxide
CFCs
Most greenhouse gases occur naturally while some (eg. CFCs) are only produced by human activities
In any one year there is a peak and a trough in the levels of CO2 in the atmosphere
Autumn, winter – trees lose leaves
» less photosynthesis but they still respire
» CO2 increases during winter but decreases
in spring and summer
Greenhouse effect
Short-wavelength infrared radiation from the Sun reaches Earth
Some is absorbed by the Earth's surface and emitted again as longer-wavelength IR radiation
The greenhouse gases absorb and then re-emit some of this long-wavelength IR radiation, which would otherwise escape into space
This then heats up the surface of the Earth
:: Human activities are polluting the atmosphere with extra greenhouse gases such as carbon dioxide
» causes a rise in the Earth's surface temp
» KA the enhanced greenhouse effect, or global warming
Effects of global warming
Polar ice caps melting
Sea level rising
Change in major ocean current
» warm water flowing in previously cooler areas
Change in global rainfall patterns
– more evaporation from the sea surface
» more water vapour » more rainfall
Change the nature of many ecosystems
– If species could not migrate or adapt quickly enough they could become extinct
Changes in farming practices would be necessary
« pests more abundant
Methane
Organic gas
Produced when microorganisms ferment larger organic molecules to release energy
The most significant sources are:
Decomposition of waste buried in the ground (landfill sites)
Fermentation by microorganisms in the rumen (stomach) of cattle
Fermentation by bacteria in rice fields
Is a greenhouse gas – although there is less methane than CO2, each molecule has a much bigger greenhouse effect
Carbon monoxide
When substances containing carbon are burned in a limited supply of oxygen they form carbon monoxide
This happens when petrol and diesel are burned in vehicle engines
Exhaust gases contain significant amounts of CO
Dangerous pollutant – colourless, odourless and tasteless and can be fatal
Haemoglobin binds more strongly with carbon monoxide than with oxygen
If a person inhales CO, more haemoglobin becomes bound to CO and so cannot bind with oxygen
Lack of oxygen reaching the cells » organs stop working
» person may lose consciousness and eventually die
Sulfur Dioxide
Formed when fossil fuels are burned, and from volcanic eruptions and lighting
Combines with water droplets in the air
Can be carried hundreds of miles in the atmosphere before falling as
acid rain
Rain normally has a pH of about 5.5 – (acidic due to dissolved CO2)
Sulfur dioxide and nitrogen oxides dissolve in rainwater to form a mixture of acids, including sulfuric and nitric acid
» rainwater is more acidic with a much lower pH
Effects of acid rain:
Death of conifers
Acidification of soil (leaching of ions into lakes kills fish, root hairs less effective at absorbing minerals » tree growth slowed)
Acidification of lake (death of bacteria and algae, fish and amphibian eggs, and change in ecosystem)
Lichen
Patterns of lichen growth can be used to monitor the level of pollution by sulfur dioxide
Different lichens KA indicator species
Appearance:
Orange crusty lichen – high
Leafy lichen on stone but not on trees – moderate levels
Shrubby lichens on trees – very low levels
Usnea-type lichens on trees – clean air
Deforestation
Tropical rainforests form a belt around areas of the Earth near the equator, in S America, C Africa and Indonesia
Have high biodiversity
Are being rapidly destroyed by humans in a process KA deforestation
10,000 hectares are cut down each year to provide timber or to clear the land for farming
Much of the clearing is done by 'slash and burn' methods – trees are cut down and burned
Adds to CO2 in the atmosphere
Removes trees which would otherwise be absorbing carbon dioxide
Adding to global warming and climate change
Other problems:
Destruction of habitats and reduced biodiversity – 50-70% of species on earth live in rainforests
Reduced soil quality – no plants to return minerals to soil when they die
– no tree roots to hold soil together
– Crops planted use up minerals
– Rain washes the minerals out
Soil is exposed due to lack of tree cover and is blown or washed away
– may be washed into rivers » rising water levels, flooding
Climate change – upset water cycle
Valuable source of many medicinal drugs and crop plants – undiscovered species will be lost
Controlled replanting schemes
KA reforestation or re-afforestation
Allowing for sustainable timber production – replacing trees that are removed and ensuring these is no ecological damage to the environment
Water pollution
Sewage
Wet waste from houses, factories and farms
If untreated sewage is discharge into waterways, then:
Aerobic bacteria in polluted water use up dissolved oxygen in the water
» kills larger animals (eg. freshwater insects, fish)
» only species adapted for low-oxygen conditions (eg. anaerobic bacteria) can survive
Untreated sewage contains pathogenic bacteria – danger to human health
De-oxygenated water moves away from the outlet and becomes oxygenated again as it mixes with clean water and absorbs oxygen from the air
» allows more clean-water species to survive
Sewage treatment – removes solid and suspended organic matter and pathogenic microorganisms so that cleaner waste can be discharged into waterways
Indicator species:
Bloodworm – heavy pollution
Caddis-fly larva – some pollution
Stone-fly nymph – clean water
Eutrophication
Large amounts of nutrients enter a body of water (eg. river, lake, sea)
Nutrients are inorganic mineral ions, usually nitrates or phosphates
Pollution by these minerals can have very harmful effects on an aquatic ecosystem
Two main sources of excess minerals:
Untreated or treated sewage
Artificial nitrate or phosphate fertilisers
Eutrophication is often cause by the use of artificial fertiliser – streams and rivers that run through agricultural land treated with fertiliser can contain high concentrations of nitrate and phosphate
Leaching – process where nitrates (which are very soluble) are washed out of soil by rain
Excess mineral ions stimulate the growth of all plants in the river or lake, seen first as a rapid growth of algae, KA
algal bloom
– algae die and are decomposed by aerobic bacteria
» oxygen in the water is used up
» fish and other animals die
« algae blocks light, decreasing photosynthesis, reducing oxygen
Severe cases – water becomes
anoxic
(very little oxygen) and only anaerobic bacteria can survive
Rapid eutrophication is less likely when farmers use organic fertiliser – nitrogen-containing compounds are less soluble so are leached less quickly