Answer:
The coastal upwelling and changes in wind and water circulation patterns is the main natural cause of dead zones.
Fertilizers cause hypoxia due to the over growth of algae on the surface of water bodies.
Explanation:
Coastal upwelling is the cause of dead zones in which water that is present in depth comes to the surface of ocean due to the movement of water because of wind. Fertilizers cause hypoxia due to the over growth of algae on the surface of water bodies. The fertilizers increases the algal growth by providing nutrients necessary for its growth. This over growth decreases oxygen concentration in water and affect marine organisms.
