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