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Organic effluent from discharge of sewage works and farms
Main pollutants are
- Nitrates - often a limiting factor, vital for plant growth. Highly soluble and leached from the soil. Sources - sewage / manure / inorganic fertiliser.
- Phosphates - often limit plant growth. Fairly insoluble. Main source - detergents in sewage.
- Eutrophication - The phosphates and nitrates in the organic effluent causes an increase in plant growth such as algae. The algae floats to the surface (algal bloom), blocking out sunlight to submerged plants. As both submerged plants and algae die, more aerobic bacteria decompose the dead matter. As the bacteria respire and multiply, they use up much of the oxygen in the water, increasing the Biochemical Oxygen Demand. This is a positive feedback system, as the decreasing oxygen levels leads to more animals dying, which in turn leads to more decomposers and so exacerbates the situation.
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).
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:
- Increased solubility of aluminium ions from soil results in increased mucus in fish gills and reduced haemoglobin efficiency
- 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
- Reduced calcium ions results in reduced mollusc nos (calcium needed for shells )
- Effect on enzymes needed for dissolving fish egg coats leads to reduced fish
- Loss of leaves in trees and decreased resistance to disease.
Lichens -are indicator species. Reduced numbers where significant pollution.
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.
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