Humans use many chemical substances for farming that consequently affect biodiversity. these compounds, which are rich in nitrogen and phosphorus, are used to fertilize crops. excessive use of these compounds causes , which leads to in bodies of water.

Execessive use of these compounds causes EUTROPHICATION, which leads to DEAD ZONES in the bodies of water.
Eutrophication is defined as the presence of excess nutrients in the water, which causes dense growth of plants and leads to depletion of oxygen that make the animals in the water to die. 
Dead zones refers to areas of low oxygen in the bodies of water caused by eutrophication and other factors that deplete the quantity of oxygen in the waters.