Question

(i) Razia saw excessive growth of blue -green algae in nearby pond of her village.
(ii) Fish which was previously in pletny were no where to be seen.
(iii)The pond is started go give a stink. Water of the pond changes its colour and is found to be not suitable for cattle. Some of the cattle who visited the pond for drinking and bathing have faled sick.
(iv) What expianatient will Razia give for these anomalies to the paniced villagers.

Answer 1

(i) Bloom forming algea occur in a pond only when the quality of pond water has crumbled due to pollution. Blue-green algae secrete toxins that are harmful to animals and humans.
(ii) Fish of the polluted pond must have died due to deficiency of oxygen in pond water. Oxygen deficiency occurs when there is excess of organic matter (called organic lodaing). The aerobic decomposers consume the dissolve oxygen. This is followed by anaerobic decomposition of organic matter. It produces sulphide and other sludge producing substances. Blue-green algae cna grow under such circumstances.
(ii) Stink from the eutrophic pond comes from anaerobic breakdown products of organic matter. The toxins released by blue-green algae further decline the quality of water causing sickness and skin rashes in animals and human beings.
(iv) Razia could explain the villagers that deterioration of pond has been due to excess of chemica fertilizers used by them in their crop fields. Rain wash brought these fertilizers into the pond. This is called eutrophication. There was initial spurt in the growth of aquatic plants due to this. Excess plant matter slowly caused organic loading of water that reduced its oxygen content killing the fish and other aquatic animals. So fertilizers should be used very judiciously in the fields. Pond should also not be used as garbage bin or septic tanks of village community.