As noted in Figure 52.15, the addition of nutrients to a lake can cause an algal bloom. When these algae die, complex molecules in their bodies are broken down by decomposers using aerobic respiration. Explain why this would reduce the lake's oxygen levels (see Concept 9.1).

A blue-green algae bloom, also known as cyanobacteria, results from a population boom in stagnant water.An algal bloom turns the entire surface of a water body green. It signifies a more significant issue known as eutrophication, which occurs when algae dominate freshwater ponds.

Decomposers break down more oversized items, such as dead animals or plants, into smaller ones.Thus, decomposers help to replenish the soil's nutrients.

When decomposers decompose dead organic materials, nutrients are released into the soil, and plants may take the nutrients released through matter breakdown as part of the nutrient cycle in ecosystems.

Aerobic respiration is a type of respiration in which oxygen is utilized as a reactant and organic fuel. Aerobic respiration is possible in the cells of most eukaryotic and many prokaryotic species. Thus, theincreased rate of aerobic respiration by decomposers lowers the oxygen level in the lake.