Question

Question 14.18 A large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping but you find an abundance of phytoplankton. Suggest a reason for the fish kill.

Class XI Environmental Chemistry Page 413

Answer 1

Excessive phytoplankton {The organic pollutants such as leaves grass , trash etc is known as phytoplankton } present in water is biodegradable. A large pollution of bacteria decomposes this organic matter in water . during this process, they consume the oxygen dissolved in water . water has already limited dissolved oxygen (10ppm) . thus it is further depleted, when the level of dissolved oxygen falls below 6ppm , the fish can't survive . Hence, they die and float dead on the lake.