Human population effects on environment Chapter 40

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

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

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

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

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

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