Background – The photosynthetic reaction and its reverse reaction, respiration, demonstrate how closely linked oxygen-breathing animals are to CO2-breathing plants. In fact, the respiration reaction shows that plants “respire” (that is, take in O2 similarly to humans) once the sun goes down. This mechanism helps explain large “fish kills” that can happen overnight in freshwater lakes adjacent to farmland that is heavily fertilized.

Scenario – You are a forest ranger in Lake Winnipissaukee  National Park, which is surrounded by farmland. You wake up one morning to find the park’s lake covered with dead fish floating at the surface. You recently measured a high concentration of NO3, a nutrient that can spur plant growth, and you suspect that this is linked to the fish kill.

Your Task: Explain how the nutrients draining into the lake from the fertilized farmland began a cycle of rapid plant growth that eventually led to the deaths of all the fish.