Human activities
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1.     Organic effluent from discharge of sewage works and farms. Main pollutants are

a.      Nitrates - often a limiting factor, vital for plant growth. Highly soluble and leached from the soil. Sources - sewage / manure / inorganic fertiliser.

b.     Phosphates - Often limit plant growth. Fairly insoluble. Main source - detergents in sewage.

Eutrophication - Phosphates and nitrates are often limiting so cause increased growth of water plants such as algae. Once nutrients are used up and light becomes limiting due to competition the plants die. This increases the detritus which will be decomposed by decomposing bacteria in the water. Increases BOD ( biochemical oxygen demand) due to bacteria respiring and using up any available oxygen in the water. Animals that need large amounts of oxygen will die eg. Trout, mayfly nymph. This leaves only animals that can cope in conditions with little oxygen eg sludge worms and bloodworms ( indicator species).

2. Heavy metal ions Mercury, lead, copper, aluminium.

Sources - Industrial run off from mining, exhaust fumes, run off from agriculture (pesticides). All Are highly toxic, act as enzyme inhibitors also act on the nervous system ( mercury).

3.     Sulphur dioxide From combustion of fossil fuels. Combines with water to form acid rain. Influence due to wind direction , amount of rainfall and type of soil. Affect on organisms :-

a.      Increased solubility of aluminium ions from soil results in increased mucus in fish gills and reduced haemoglobin efficiency

b.     Increased acidity reduces activity of decomposers reducing availability of phosphates and nitrates leading to oligotrophic conditions, clear nutrient lacking lakes and streams. Reduced plant and animal diversity. Diversity index - need to know numbers of species and total number of individuals.

c.      Reduced calcium ions results in reduced mollusc nos ( calcium needed for shells ).

d.     Effect on enzymes needed for dissolving fish egg coats leads to reduced fish.

e.      Loss of leaves in trees and decreased resistance to disease.

Lichens -are indicator species. Reduced numbers where significant pollution.

4.     Crude oil

From oil spills, washing tanks and accidents.

·         Reduced light penetration - reduced photosynthesis.

·         Reduced surface tension

·         Oil film prevents oxygen entering water.

·         Oil is toxic, absorbed via digestive system and lungs. Can accumulate through food chains.

·         Coating feathers and fur results in reduced insulation / flight/ buoyancy.

·         Coating gills prevents oxygen absorption.

Solutions - Booms to reduce spread. Detergents ( are also toxic ).

Conservation

Active process that aims to keep ecosystems stable as environmental conditions change.

Methods

·         Set aside - provides a wider range of habitats- food plants and breeding sites for animal species.

·         SSSI’s and nature reserves- havens for threatened species.

·         Captive breeding programmes - to allow release into wild.

·         Changes in agricultural practice - reduced use of herbicides, pesticides and fertilisers. Reduced drainage of wetlands. Reduced grazing pressure.

Other Notes in this Category

1. Adaptations for survival - Methods of avoiding extremes of climate.
2. Cycling Systems
3. Human activities
4. Recycling of Materials
5. Variations in Nutrient Supply

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