Question

Described below are the three steps in the process of how eutrophication leads to total destruction of aquatic life. Choose the option which has the correct sequence of these steps.

i) Algae dies, producing a large quantity of organic matter.
ii) Bacteria begin degrading organic matter, leading to a decrease in dissolved oxygen.
iii) Increase in nutrient concentrations causes a sudden growth spurt in algae.

• A. $i\to iii\to ii$
• B. $ii\to i\to iii$
• C. $iii\to i\to ii$
• D. $i\to ii\to iii$

Answer 1

The correct option is C $iii\to i\to ii$

$\bullet$ In the process of eutrophication, initially there is an increase in nutrient concentration in the water body, which causes algal bloom.
$\bullet$ This algal bloom leads to an increase in the Biological Oxygen Demand. Eventually, the algae start to perish and leave behind a lot of organic matter.
$\bullet$ The bacteria present in the water body begin decomposing the organic matter.
$\bullet$ This decomposition demands huge amounts of oxygen, which ultimately reduces the dissolved oxygen levels in water.