Chemical fertilizers used in farms may be washed into local water bodies, such as ponds and lakes. this often results in a rapid growth of algae, an algal bloom in the ponds and lakes.

The correct answer is a nutrient runoff.  

Nutrient runoff is a major reason for eutrophication of surface waters, in which extra amount of nutrients, generally phosphorus or nitrogen, instigate growth of algae. Sources of nutrient pollution involve surface runoff from pastures and farm fields, emissions from combustion, and discharges from septic tanks.  

b. heterotroph

explanation: