Algal blooms occur due to the presence of an excess amount of nutrients, like phosphorus, in fresh water. how does excess phosphorus get into fresh water?

The algal blooms are illustrated as the rapid development of algae in the water bodies. These algal blooms are an outcome of the excess concentrations of nutrients, like phosphorus in the water body. The discharging of these nutrients in the freshwater bodies takes place due to washing away of the fertilizers from the nearby agricultural fields.  

The fertilizers are enriched in nutrients like phosphorus, which helps the plant to grow. When they washed into the water bodies, they encourage the development of the algae, resulting in an algal bloom.  

"d.) carbon dioxide and hydrogen sulfide"