Question

Two types of aquatic organisms in a lake show specific growth patterns as shown below, in a brief period of time. The lake is adjacent to an agricultural land extensively supplied with fertilisers.

Answer the questions based on the facts given above:

(i) Name the organisms depicting the patterns A and B.

(ii) State the reason for the growth pattern seen in A.

(iii) Write the effects of the growth patterns seen above.

 

Answer 1

(a) A - Fish and clean water organisms depict dissolved oxygen; B - Decomposers depicts biochemical oxygen demand (BOD).

(b) As the sewage is decomposed, there is a gradual rise in the dissolved oxygen downstream with the reappearance of fish and other clean water organisms. This leads to the recovery of river from sewage water.

(c) Effects on aquatic life:

• (iv) It causes high mortality rate among aquatic animals.
• (v) The excessive nutrients facilitate algal growth causing algal bloom.