Eutrophication Guide, Meaning , Facts, Information and Description
as imaged from orbit.]]Eutrophication is the enrichment of an aquatic system by addition of nutrients. It is typically caused by leached phosphorus or nitrogen containing compounds into lakes, rivers, bayss, or other semi-enclosed waters (even slow-moving rivers). Some algae and blue-green bacteria thrive on the nutrients and a population explosion—in the case of algae, known as an algal bloom—occurs. Eutrophication was recognized as a pollution problem in European and North American lakes and reservoirs in the middle of the twentieth century (Rohde, 1969). Since then, it has become more widespread, causing deterioration of aquatic environments and serious problems for water use, particularly drinking-water treatment (Bartram, et al., 1999). Surveys have shown that in the Asia-Pacific Region, 54% of lakes are eutrophic; in Europe, 53%; in Africa, 28%; in North America, 48%; and in South America, 41% (ILEC/Lake Biwa Research Institute, 1988-1993).
Such "explosive" growth is usually unsustainable in natural systems. Perhaps because a nutrient or some other factor becomes limiting, the populations in "bloom" eventually crash (death of numerous individuals occurs). An adverse impact of eutrophication on aquatic systems is depletion of oxygen. Oxygen is required by all respiring plants and animals in an aquatic environment and it is replenished in daylight by photosynthesizing plants and algae. Under eutrophic conditions, dissolved oxygen is reduced by the dense population, and additional oxygen is taken up by microorganisms feeding on dead algae. When dissolved oxygen levels decline, especially at night when there is no photosynthesis, fish and other animals in the water may suffocate. In extreme cases, anaerobic conditions ensue, promoting growth of bacteria such as Clostridium botulinum that produces toxins deadly to birds and mammals. Zones where this occurs are known as dead zones.
Eutrophication is exploited in many man-made aquaculture schemes.
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