1. Human population effects on environment
Chapter 40

2. Chemicals on wildlife
Chemicals entering food chains can have massive ‘side effects’ if….
They are non-specific
Non bio-degradeable
In excess concentration
DDT:
Persistent & toxic
Affected bird egg shells
Can wash into waterways & oceans
However, soon resistance in insects developed
Due to persistance & resistance, DDT now largely banned
Non-specific chemicals can disrupt natural food chains
Natural predators of certain pests can be killed – pests thrive
Can aid algal blooms

3. Interdependence of community members
Producers, consumers & decomposers exist interdependently
Ecosystems are delicately balanced
Species removed = dependent species affected
More disruption = more ecological instability

5. Disruption of Nitrogen Cycle
Algae
Photosynthetic microbes – mainly live in water
Require light, CO2, nutrients & suitable temp to grow
If all are plentiful – algal blooms can occur
Natural in spring & autumn
Eutrophication
– enrichment of waterway with nutrients
Fertilisers, sewage & detergents all rich in nitrates & phosphates
- with sunlight & warm temp = artificially high eutrophication
Common in offshore waters

6. Effects of algal blooms
Dissolved oxygen levels depleted
– algae decomposed by aerobic bacteria
Reduction in light
– water plants deprived of light
Some algae produce poisons
- enter food chain
Inadequate sewage treatment
– huge quantities of nitrogen compounds
Increasing population
= increasing sewage treatment problems (North Sea, open sewers)
Nitrates in drinking water
– mainly harmless? (‘blue-baby syndrome’?)
50-100ppm max concentration – WHO guidelines

8. CO2,Carbon Cycle & Methane
CO2 levels should be maintained by carbon cycle
Increased fossil fuel use
= 5 billlion tons of CO2 into atmosphere
Excess CO2 disrupts carbon cycle
- aggravated by deforestation
Methane – component of natural gas
- from anaerobic decomposition
Produced by a range of sources
E.g anaerobic bacteria, cattle flatulence
Burning of tropical forests & land-fills also release methane
CFC’s (man made) also in the atmosphere

9. Greenhouse Effect CO2, Methane, CFC’s
– all trap heat from earth (‘Greenhouse Gases’)
Vital for supporting life on earth – ‘Greenhouse Effect’
Evidence suggests excessive global warming in recent years
The future:
Increasing ‘greenhouse gases’
Increasing global temperatures
Rise in sea level (flooding etc.)
Climate change
Agriculture - many areas unable to support crops
Wildlife – mass extinctions, ecosystem destruction
Course of action
More efficient energy usage
Alternative energy sources
Financial incentives to prevent deforestation
Strict control of CFC’s etc