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Biology 3A – human impact
Salinity• Trees have long roots
and draw up water from deep underground – keeping water table low
• Grasses have shallow roots and do not draw up the same amount of water
• When trees are cleared for pasture or houses, the water table rises, bringing salts to the surface
Deforestation• Forests provide habitat for a
number of rare species• Removal of habitat leads to
loss of these species• Large amounts of
vegetation increase humidity – removal can change rainfall patterns
• Loss of vegetation often leads to erosion, salinity and desertification
• Forests are a way of fixing CO2 – as trees are large, slow growing and long lived, so removing trees increases green house effects
Desertification
Main causes • clearing for houses, farms, mining etc
Main effects • loss of soil fertility• loss of habitat • soil erosion • Salinity• decreased humidity and rainfall• damage to waterways – fertilizers & pesticides
Eutrophication• Increased nutrients (especially nitrates and phosphates) from fertilisers,
detergents and sewage enter water ways• Blue-green algae increase growth rate leading to population explosion• This rapid growth uses up the oxygen in the water, causing other
organisms to die, and then the blue-green algae to die• Many species of blue-green algae produce toxins – when population
numbers are high these are produced in such large numbers that they kill other water life
• As there is little or no oxygen, dead organisms rot anaerobically – leading to the bad smell
Ecological magnificationThis is build up of pollutants eg
insecticides, heavy metals in a food chain. The higher order consumers and detrivores have the highest levels
Problems seen include• Death of top order consumers eg
hawks, falcons• Plagues of lower order
consumers due to lack of predators eg mice plague because owls have been poisoned
• Heavy metal poisoning in people eating high order consumers or detrivores eg shellfish
Enhanced Greenhouse effects - global warming• Main causes
Build up of greenhouse gases in the atmosphere – carbon dioxide (combustion), methane (ruminants & rotting garbage) & CFC’s (refrigerators & air conditioners)
• Main effects
Increased global temperatures Rise in sea levels (thermal
expansion & polar icecap melting)
Melting of glaciers
Changes in weather patterns – some places (eg Australia get dryer, others getter wetter)
• Possible solutions
Reduce emissions
Plant more trees, use less fossil fuels, reduce ruminants
Normal –Some greenhouse gases present
Global warming–Increased greenhouse gases present
Radiation from sun reaches EarthSome absorbedSome reflected and leavesSome reflected, but bounces back and warms Earth
Radiation from sun reaches EarthSome absorbedLess reflected and leavesMore reflected, and bounces back and warms Earth
Enhanced Greenhouse effects - global warming 2
Global currents & climate
Global currents drive many of our weather patterns and also determine productivity of many marine ecosystems
A change in salinity at the ventilation areas could lead to a reduction in the current changes in climate.A decrease in surface temperature means less CO2 is trapped
Climate change – is it happening?
Athabasca glacier
Previous ice level
Food resources scarcer so bears are looking after cubs for 2 years, instead of 1 breed every 3rd year instead of every 2nd year
Average rainfall decreasing
Healthy pines
More pines are affected by pine beetle – winters not cold enough to kill off adult beetles
Lake Louise – May 26th 2008 (last month of spring) – still frozen
Pines affected by pine beetle
Deterioration of the ozone layer• Main causes
CFC’s, halons & methyl bromine (& jet planes) destroy ozone in atmosphere
• Main effects
Ozone (O3) absorbs UV radiation.
If ozone is reduced more radiation gets through
This leads to increased temperature
Higher radiation increase risk of skin cancers & eye problems in people, higher risk of mutation & damage in unicellular organisms
Damage to algae may cause loss of biomass/ ecosystem collapse in marine ecosystems
• Possible solutions
Reduce use of CFC’s
Care with disposal of gases (eg old refrigerators, servicing air conditioners
Normal Ozone prevents most of UV radiation from entering
Ozone depletionLess ozone means more UV radiation can enter
Ozone depletion
Ozone depletion over south poleDobson units measure amount of ozone present