FHSST Biology/Contents/Index/ES/Human Influence/Water

Petroleum installations produce some lethal effluent problems. Open cast mines also cause acidification of water (look up some SA examples). Open pit mining causes eutrophication of streams from top soil nutrient dumping.

Contamination by oil:

Crude oil spills are most serious pollution source, The flammability of oil, its toxicity to plants and animals and the aesthetic effects of oil make it a serious polluting agent. In the marine environment, there are two main sources of contamination. One is the chronic effects of losses from refining, shipments, tanker cleaning and other accidental spills. The second source are the acute incidents where a large amount of oil is lost during an accident. Oil can kill organisms directly through coating and asphixiation, and kill be poisening via contact or ingestion. Water –soluble toxic compounds can be lethal to fish and invertebrates and result also in the destruction of the sensitive eggs and larval forms of fish. Disruption of the body insulation of birds. Oil may have an effect on food chains, if one major prey or predator species is effected. Aquatic areas affected by chronic oil spillage may have a lowered species biodiversity and fluctuations in oxygen concentration. Oil may inhibit photosynthesis by phytoplankton. Polar regions are most at danger from oil spills, as the low temperature slows down the breakdown of oil and polar aquatic organisms tend to have long life cycles. Coral reefs are also in grave danger from oil spills as they recover slowly and affected coral reef may be eroded away. Many cleanup techniques are aimed at cleaning up the intertidal zone for the benefit of tourism but to the detriment of other parts of the ecosystem. Emulsifiers and chalk make oil contamination a danger for the benthos and open ocean and scraping of beaches causes much biological damage.

PCB’s . These are a group of organic substances in paint, inks and carbonless copy paper. These substances are long lasting and soluble in fats. It has been found at high trophic levels in food chains and effect the metabolism and waterproofing of sea birds. People where effected in Japan with high levels of PCB’s causing skin ailments.


The introduction of large amounts of nitrogen and phosphorus into surface fresh waters is a major cause of eutrophication. In un-impacted ecosystems phosphorus is scarce and is a limiting factor to population growth of species within an ecosystem. Large inputs of phosphorus into an aquatic ecosystem may cause a aquatic macrophyte bloom, after which nitrogen may become the limiting factor. After nutrients in the water are depleted, these macrophytes start dying and decaying, causing anaerobic conditions within the aquatic ecosystem. This process has resulted in changes in the fauna of impacted ecosytems, generally in lower biodiversity.