(i) The pattern A is depicted by microorganisms and pattern B is depicted by fishes or any other aquatic organism.
(ii) As the lake is adjacent to an agricultural land extensively supplied with fertilisers, the run-off water from the field will result in increase in nutrients of lake. Thus, number of microorganisms will rise to degrade organic matter.
(iii) As the microorganisms increase (depicted by pattern A), they result in decrease of dissolved oxygen in water thus causing decrease in number of aquatic organismis like fish, etc. (depicted by pattern B)..