What is a common consequence of introducing excess nutrients into aquatic systems?

Introducing excess nutrients into aquatic systems often leads to a phenomenon known as eutrophication. This process occurs when nutrient levels, particularly nitrogen and phosphorus, significantly increase in water bodies. As a result, algae begin to proliferate, sometimes leading to harmful algal blooms which can produce toxins harmful to aquatic life and even to humans.

Eutrophication can cause several negative impacts, such as depleted oxygen levels in the water due to the decay of algal blooms. This depletion can create "dead zones" where aquatic life cannot survive, leading to reduced biodiversity and disruption of the ecosystem. Additionally, as the algal blooms die and decompose, the process can further exacerbate the depletion of oxygen.

In contrast to other options, which suggest benefits like increased biodiversity, improved water clarity, or reduced water temperatures, the reality of nutrient over-enrichment results in detrimental effects that harm aquatic environments and reduce overall ecological health.