What is one major source of phosphorus other than natural deposits?

Sewage discharge is a significant source of phosphorus due to its role in nutrient pollution. When human waste and industrial effluents containing phosphorus enter water bodies, they can contribute to the excessive availability of this nutrient in aquatic ecosystems. This can lead to algal blooms, which deplete oxygen levels in the water and disrupt aquatic life.

Sewage often contains detergents, fertilizers, and other phosphorus-rich compounds that can enhance the nutrient load in rivers and lakes. This anthropogenic contribution is critical to consider when managing water quality, as phosphorus from sewage can lead to eutrophication, negatively impacting both freshwater and marine environments.

While other choices include various forms of water and gases, they do not significantly contribute to phosphorus levels in the same way as sewage discharge.