Question

The pH of the epilimnion of a lake could potentially change with the stocking of a piscivorous fish in a lake that previously contained only planktivorous fish. A) would the pH in the epilimnion increase or decrease? B)Explain the biological mechanisms that caused the change in pH. C) Explain the chemical mechanisms that would be responsible for the change in the pH.

Answer 1

A) Upon stocking of piscivorous fish pH in the epilimnion should decrease (become acidic).

B) previuosly because of the presence of planktivorous fish there will be less alagalgrowth, hence pH should be on alkaline side. usually green algae produce acids upon death by bacterial decompostion, which strips oxygen from the lake and lake becomes acidic or pH is decreased. less algal grpwth and abundance of planktivorous fish should result in increase in pH on alkaline side (because of ammonia release by the abundant planktivorous fish). Introducing piscivorous fish should decrease planktivorous fish abundance and increase in algal growth and decompostion results in acidification of the lake.

C) In the presence of piscivorous fish, algae grow abundantly, dead alagae sink to the bottom of the lake and bacteria and fungi decompose them and take all the dissolved oxygen and releasing carbondioxide (CO2+H2O-->Carbonic acid) and more protons resulting in acidity of the lake. And freshly growing algae produces acids which also contributes to decrease in ph lake becomes acidic