What are the main causes of algal blooms?

Algal blooms are primarily driven by an increase in certain nutrients, particularly nitrogen and phosphorus, which can lead to rapid algae growth. Conditions that favor algal blooms typically include ideal temperatures that promote growth, ample sunlight that supports photosynthesis, and the presence of specific types of algae that thrive under these circumstances. Warm water temperatures combined with enough light allow algae to reproduce quickly, resulting in an algal bloom.

In this context, the correct choice accurately highlights the essential factors contributing to algal blooms: nutrient availability, temperature, sunlight, and the presence of specific algae species. The ecosystem’s dynamics can be greatly affected when these conditions align, often leading to significant ecological challenges, such as depleted oxygen levels and harmful impacts on aquatic life.

Other factors presented, such as a lack of sunlight and cold temperatures, would inhibit algal growth rather than promote it, while excessive rainfall and low nutrient levels would also not create the conditions needed for blooms to occur. High salinity and low water flow can affect certain aquatic environments, but they are not primary drivers of algal blooms as defined in this context.