Question

(i) Razia saw excessive growth of blue-green algae in nearby pond of her village.
(ii) Fish, which was previously in plenty were nowhere to be seen.
(iii) The pond has started stinking. 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 fallen sick.
​(iv) What explanation will Razia give for these anomalies to the paniced villagers?

Answer 1

(i) The excessive growth of blue-green algae occurs when the water of the pond becomes polluted. These organisms secrete certain toxic substances, which cause a wide range of diseases.

(ii) Due to excessive algal growth, the dissolved oxygen of the pond water depletes. This depletion of oxygen results in the death of fishes, which depend on dissolved oxygen for survival.

(iii) The stinking of the pond is a result of the anaerobic metabolism, which could have been performed by microbes in the limited supply of dissolved oxygen. Moreover, the toxins produced by algae can cause diseases such as bovine blue-green algae toxicosis in animals.

(iv) In the given case, Razia can explain to the villagers that excessive growth of algae was caused due to the deposition of chemical fertilizers in the pond. This deposition was caused due to runoff of rainwater, which dissolved the chemical fertilizers used in the farms. This lead to the abrupt growth of algae which released toxins and depleted dissolved oxygen of the pond. This resulted in the death of fishes of the pond and it also sickened the cattle. Thus, chemical fertilizers should be used judiciously to prevent excessive algal growth.