Recall that areas with high net primary productivity not only produce high levels of biomass rapidly, they also take up large amounts of co 2 and give off large amounts of oxygen. what is the likely result of the increasing amounts of fertilizers in the major rivers emptying into oceans?

The most probable result of the increasing concentrations of fertilizers in the prime rivers emptying into oceans is eutrophication followed by hypoxia. This will eventually result in less uptake of carbon dioxide and less release of oxygen.  

The fertilizers are among the common pollutants, which degrade the quality of water. The fertilizers comprise chemicals, which are good for plants use, however, the excess amounts used in plants get run off and pollute the water bodies.  

The fertilizers mainly comprise nutrients like phosphorus and nitrogen. When it rains, these nutrients get carried to the water bodies and results in algal bloom known as eutrophication. This algal bloom utilizes the oxygen in the water, leaving behind no or fewer levels of oxygen that hampers life of aquatic species.