Which nutrient is a limiting nutrient in aquatic ecosystems and, when

Correct answer: B) Phosphorus.
Phosphorus is often the limiting nutrient in aquatic ecosystems, meaning that its availability controls the growth and productivity of aquatic organisms, particularly algae.
When phosphorus is added to aquatic environments, such as through runoff from agricultural fertilizers, sewage discharge, or other sources, it can lead to an excessive growth of algae, known as an algal bloom.

Algal blooms can have several negative impacts on aquatic ecosystems:
Eutrophication: The excessive growth of algae can lead to eutrophication, where the water becomes overly enriched with nutrients, depleting oxygen levels and causing the death of other aquatic organisms.
Toxicity: Some types of algae can produce toxins that are harmful to aquatic life, as well as to humans and animals that use the water.
Disruption of the food web: Algal blooms can outcompete and displace other primary producers, such as aquatic plants, disrupting the entire food web and ecosystem balance.
In contrast, the other nutrients mentioned in the options (hydrogen, potassium, and calcium) are not typically considered limiting factors in aquatic ecosystems or the primary drivers of algal blooms.

Therefore, phosphorus is the correct answer as the nutrient that is a limiting factor in aquatic ecosystems and can cause algal blooms when added to these environments.