Question

Why do nutrients like nitrate and phosphate ions often lead to a decrease in aquatic life?

chemistry

Answer 1

Though nitrates and phosphates acts as nutrients for aquatic plants and organisms, they are harmful when present  in excess quantities. Plants take nitrogen in the form of nitrates for their growth and phosphates are also essential for their metabolic reactions.

Algae use nitrates for their growth and if excess amount of nitrates are available, then growth of algae occurs in uncontrolled fashion and huge amount of algae covers up the water and causes variations in amount of dissolved oxygen which will in turn effect the aquatic organisms. Since the algae covers up the surface of water, the amount of sunlight that enters the water body also reduces. Aquatic animals like fish need some sunlight to survive and it is hampered by the excess algae. which will be When the excess algae dies, the bacteria that feeds on algae and decaying algae will consume dissolved oxygen.

Sulfates in excess quantity is toxic for aquatic life and sulfates can form strong acids with change in pH leading to harmful effects. The process through which excess amounts of nitrates and phosphates are acquired in a water body is called Eutrophication.