The phosphorus cycle is the movement of phosphorus around the biosphere. Phosphorus rarely changes form. It is typically found as phosphate. Phosphate is not very soluble in water. Weathering brings phosphorus to terrestrial and aquatic habitats. It is held tightly by soil. Phosphorus is a limiting nutrient in many aquatic systems.Small inputs greatly increase growth of producers. Algal Bloom- Rapid increase in the algal population of a waterway. Detergents are a major source of phosphorus.