Eutrophication
href="http://www.chempapy.blogspot.com/">Eutrophication is the name given to the release of large amounts of phosphate and nitrate or organic matter into water resulting in a lowering of oxygen levels and change in the fauna of the water. In their natural state most waters, whether freshwater or marine, contain only low levels of nitrate and phosphate, although natural examples of eutrophic lakes are known.
Is a process whereby water bodies, such as lakes, estuaries, or slow-moving streams receive excess nutrients that stimulate excessive plant growth (algae, periphyton attached algae, and nuisance plants weeds).This enhanced plant growth, often called an algal bloom. (Blue-green algae called Mycophyceae e.g. Anabaene flos-aquae);If substantial quantities of these minerals enter water, they allow large numbers of algae, cyanobacteria and aerobic bacteria to build up.
These organisms can require so much oxygen in the water to the point at which aerobic bacteria are unable to decompose organic matter in the water.One standard way of determining the oxygen requirements of an area of water is to measure the rate at which the oxygen level of a sealed sample of the water falls when kept in the dark for five days at 200C. (Keeping the sample in the dark stops photosynthesis which would otherwise lead to oxygen being evolved by any photoautotrophs in the sample.)
The biological oxygen demand (BOD) of unpolluted river water is typically less that 5mg O2/l/5 day. Crude sewage has a BOD of around 600 mg O2/l/5 day.It is not surprising that pollution due to sewage can lead to permanent changes in the organisms found in the affected waters.
However, good sewage treatment reduces the BOD of discharged effluent to less than 30mg O2/l/5 day.Biological indices can be used to measure the extent of organic pollution in water systems.
In England and Wales, a survey of rivers in 1980 classified rivers into five types on the basis of their dissolved oxygen concentrations, ammonia concentrations and ability to support fish.
At the same time the invertebrates were sampled.In this system, points are allocated according to whether or not certain key groups are present.one advantage of this method is that invertebrates need only to be identified to family level.Oligochaetes and chironomids are found even in highly polluted streams and rivers with very low levels of dissolved oxygen (<10 and="" are="" at="" dissolved="" extreme="" families="" flies="" found="" high="" in="" levels="" mayflies="" most="" of="" only="" other="" oxygen="" saturation.="" stone="" the="" waters="" with="">80% saturation).
One major advantage, to an ecologist, of using a biological index such as this one is that it provides a measure of the organic pollution in the water over a reasonably long period of time.
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A single release of fertilizer, for example, into a river may pass undetected by chemical analyses a few weeks later.However, that one incident may have killed key indicator families which can still be absent months later.
NOTE;Eutrophication: a process by which a body of water progresses from its origin to its extinction. This process happens in stages.
Sources of Nutrients
Eutrophication is a natural process however, humans in their everyday activities can exacerbate the process:
Point sources (can locate the cause)
Sewage treatment plant discharges
Storm sewer discharges
Industrial discharges
on-point sources (can’t locate the cause, it’s everywhere)
Atmospheric deposition
Agricultural runoff (fertilizer, soil erosion)
Septic systems
Bad taste and odor : some of the algal species that "bloom" produce toxins (geosmin, MIB), water taste and odor deteriorates.
Oxygen depletion: penetration of light into the water is diminished. This occurs because the algae forms mats as a result of being produced faster than they are consumed. Diminished light penetration decreases the productivity of plants living in the deeper waters and hence their production of oxygen.
Under anoxic conditions iron, manganese, ammonia and phosphorous are released into the water column, anaerobic bacteria flourish, producing hydrogen sulfide.
Effects on water quality
Effects on treatment costs and compliance
Bad taste, odor, and high organics increase operational costs.
Compliance with local and international regulations becomes more difficult to achieve.
Effects on recreational activities
Recreation: Lowered oxygen results in the death of fish that need high levels of dissolved oxygen "DO"), such as trout, salmon and other desirable sport fish. The community composition of the water body changes, with fish that can tolerate low DO, such as carp predominating.
Changes in fish communities have ramifications for the rest of the aquatic ecosystem like the explosion of mosquitoes.
Effects on biodiversity
Decrease in the diversity of zooplanktons due to death of some which can not tolerate the situation.
Disease to humans e.g. Blue Baby syndrome, which can result to death.
Increase of phytoplanktons e.g. algae
Blue Baby Syndrome
Is the illness that occurs when a child drink water containing large amount of nitrates.
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The body’s digestive system converts nitrates to nitrites, (using E. coli) changing oxyhemoglobin to metheglobin, which cannot carry oxygen. Mucous membranes turn blue, impairing functions.
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