Which condition can lead to an increase in harmful algal blooms?

Harmful algal blooms (HABs) are often exacerbated by excessive nutrient runoff from agricultural practices. This runoff typically consists of high levels of nitrogen and phosphorus, which can come from fertilizers, manure, and other agricultural inputs. When these nutrients enter water bodies, they can stimulate the rapid growth of algae, leading to blooms that may be harmful to aquatic life and ecosystems.

The presence of excess nutrients provides the ideal conditions for certain algal species, particularly cyanobacteria, to proliferate. These blooms can deplete oxygen in the water, produce toxins, and disrupt the aquatic ecosystem. In contrast, low nutrient availability would not support the growth of these algal populations. Proper water circulation might help distribute nutrients but does not inherently promote the growth of algae. High biodiversity in a water body generally contributes to a more stable ecosystem and can often mitigate the effects of nutrient overload by promoting competition and habitat complexity. Therefore, the relationship between nutrient runoff and harmful algal blooms is clear, establishing excessive nutrient runoff as a primary factor contributing to the occurrence of these blooms.