Here's a problem to solve: Around areas of increased fertilizer runoff, all of the heterotrophs within a lake food chain may show an increase in numbers. After the initial increase, the populations begin to decline. Which event most likely caused the populations to decline?

Among the 4 following options, which is the correct answer?

- A: More predators were introduced into the lake.
 
- B: Water was depleted of nutrients such as nitrogen.
 
- C: Breeding season for the organisms came to an end.
 
- D: Decomposing algae lowered the amount of dissolved oxygen.
 