What is the role of reactive phosphorus in an aquatic ecosystem?

Reactive phosphorus plays a significant role in an aquatic ecosystem primarily by stimulating algal growth. In its reactive form, phosphorus is a key nutrient that often limits biological productivity in many freshwater systems. When phosphorus is available in sufficient amounts, it can lead to eutrophication, which is the rapid growth of algae and aquatic plants. This algal bloom can drastically alter the ecosystem, leading to decreased water clarity and oxygen depletion as the algae die and decompose. The effects of excessive algal growth can be detrimental to aquatic life, potentially creating dead zones where oxygen levels become too low to support most marine organisms.

The other options do not accurately represent the primary ecological role of reactive phosphorus. While it contributes to nutrient cycling in aquatic environments, its primary influence is on algal growth rather than directly providing calcium, filtering water, or affecting pH levels in a significant or direct manner. Therefore, recognizing the role of reactive phosphorus in stimulating algal growth is crucial for understanding aquatic ecosystem dynamics and the potential consequences of nutrient loading.