What is an algal bloom?

An algal bloom is defined as a rapid increase in the population of algae in aquatic environments, primarily due to the availability of excessive nutrients, particularly nitrogen and phosphorus. These nutrients often come from runoff, agricultural fertilizers, and wastewater, which can lead to eutrophication—an over-enrichment of water bodies that fosters high growth rates of algae.

During an algal bloom, the proliferation of algae can severely disrupt aquatic ecosystems. It can lead to decreased sunlight penetration, which limits the growth of other aquatic plants and organisms. Additionally, when these algae die and decompose, a significant depletion of oxygen in the water can occur, resulting in hypoxic conditions that harm or kill fish and other marine life.

The other responses do not accurately represent the specific phenomenon of algal blooms. The increase in bacterial populations is a separate issue that may arise from organic material decomposition but is not the same as a bloom of algae. The process of algae producing oxygen is part of their normal function during photosynthesis, but it does not define an algal bloom. Lastly, while water contamination by chemicals can contribute to the conditions that create algal blooms, it does not describe the bloom itself. Thus, the focus on the drastic increase due to excessive nutrients makes option B