A lake near a village suffered heavy mortality of fishes within a few days Consider the following reasons for this?
(a) Lots of urea and phosphate fertilizers were used in the crops in the vicinity.
(b) The area was sprayed with DDT by an aircraft.
(c) The lake water turned green and stinky.
(d) Phytoplankton population in the lake declined initially thereby greatly reducing photosynthesis. Which two of the above were the main causes of fish mortality in the lake?

Options

A. (A), (C)
B. (A), (B)
C. (B), (C)
D. (C), (D)

Answer

B

Explanation

By the excessive use of agricultural fertilizers and pesticides it increases the prime contaminants such as nitrates and phosphate which act as plant nutrients. They over stimulate the growth of algae causing unsightly scum. And unpleasant doors and decrease the water of dissolved oxygen vital to other aquatic life. This phenomenon is called eutrophication.