how can we prevent ocean dead zones from occuring around the world?

Answer 1

Nitrogen runoff from farm fertilizers, sewage, and air pollution is one of the big causes of ocean dead zones. When the nitrogen flows to the sea, it acts as a fertilizer to plankton. The abundant plankton use up all the ocean's oxygen.
Mitigation:
Reducing the discharge of nitrogen to rivers by reducing runoff, using less fertilizer, reducing nitrogen emissions from cars and factories, treating sewage better.