The rate of reoxygenation becomes slower than the rate of de-oxygenation. At this time, BOD of the water become very high, indicating a heavy degree of pollution. Phosphorus as phosphate is most useful algal nutrient. it along with nitrogen (nitrates) stimulates alga growth and as a result algae now covers
almost the entire water surface. This excessive growth of algae is called water bloom or eutrophication.
This also significantly reduces the B.O.D

Algal Bloom and Eutrophication

When water body becomes rich is nutrients (due to excess of sewage and other blue-green algae) becomes very high organic contents), the growth of algae (especially blue this growth of algae is called algal bloom.

Algal blooms compete amongst the constituent algae for light and ow algal bloom totally covers the water surface and reduces the dissolved Moreover, at the same time, algae release toxins harmful for aqua results in death of aquatics organisms.

This process of nutrient enrichment of water and consequent loss of aquatic organisms is known as eutrophication.

Polluted water can not be used for drinking purposes. It is likely to cause water borne diseases, commonest being the infection of E. coli, typhoid, dissent gastroenteritis, hepatitis, etc.

The decomposing matter releases foul smelling gases. The entire water reservoir becomes ugly looking and generally can not be used.

Industries release their wastes, in the drains which carry these effluent’s to water reservoirs like lakes, rivers, etc. The wastes differ in their composition depending upon the type of industry and the treatment of the raw materials used.

(b) Industrial Waste Water

Following is the list of different wastes released by a variety of .industries

Inert suspensions such as dust, coal ash, etc.

Poisons like acids, alkalies, phenols, cyanides, mercury, copper, zinc, etc.

Inorganic reducing substances like ferrous salts, sulphides, sulphites, etc.

Oils. Organic residues like effluents from tanneries, paper mills, sugar factories and farms etc.

Increase the amount of toxic substances in the water body may lead to the death of the aquatic organisms.

Increase the amour feres the metabolism of ount of suspended solids also interferes the metabolism ou aqatic animals.

Increase in the amount of organic and inorganic matter consumes the as Organic matter consume the dissolved oxygen (OD)in water for their decomposition. This increases chemical oxygen
as contaminated ad unsafe for aquatic organisms).

Release of hot waste-water, having 8 to 10°C temperature may damage some sensitive algae. This is called thermal pollution.

Effects of metals

following are the effects of some of the metals found in polluted water.

(i) Mercury : This is released by chlorine and caustic soda manufacturing industries. It Treaches man through the food chain Formed by aquatic organisms such as and gets bioconcentrated or biomagnified. It affects nervous system causing madness leading to death.

Japan’s Minamata bay is a famous example of disaster of eating mercury polluted fish causing large number ol deaths. Mercury poisoning is therefore known as Minamala disease.

(ii) Lead: It is released by the outlet pipes carrying effluents and gets collected on water surface. Lead accumulates in animal tissues and damages them. Continuous accumulation of lead in man over a long period of Tume affects gastrointestinal
tract, neurO-muscles and central nervous system.

(iii) Copper and zinc: These get collected in the members of mollusca and affect their
growth, metabolism and reproduction.

(iv) Cadmium and chromium: These metals accumulate in the body of marine organisms
and cause their death. Cadmium pollution can cause ital-itai disease (a painful disease of bones and joints) and cancer of liver and lung.

(iv) Fluoride pollution: Fluorine occurs in water, soil and air. Fluoride is known to Cause dental tuorosis. Use of fluoride containing water causes stiffening of bones, mottling of teeth, outward bending of legs from knees (knock-knee syndrome),
etc. Fluorides also destroy the leaf tisues.

(c) Oil Spills

An oil spill is the accidental discharge of petroleum in ocean and estuaries. This results in heavy oil pollution. The main sources of oil pollution are oil refineries, tankers, Offshore oil mining etc.

Effects

Oil cover lead to the death of planktonic organisms, fishes and marine birds.

Oil spills are also harmful to coral reef.

(d) Pesticide Pollution

Term pesticide includes insecticides, fungicides, rodentisides, herbicides, weedicides, biocides and soil fumigants.

Tags: Algal Bloom and Eutrophication