A pond shows the presence of algal bloom in it. For night-time, what is the interpretation with respect to the amount of oxygen and nitrates dissolved in that water?

Some algal blooms are the result of excess nutrients (nitrates) in the pond. These nutrients in water cause increased growth of algae and green plants.

As more algae grow, others plants die. This dead organic stuff becomes food for bacteria that will decompose it. With more food available, bacteria increase in number and consume dissolved oxygen in the water. When the dissolved oxygen content decreases, many plants, fish and aquatic insects cannot survive.

This will result in a dead area.

the cinema would be a very good place to go.