Describe how this algal bloom

might alter the local nitrogen cycle in that ecosystem.

Some algae bloom change the nitrogen cycle in the ecosystem, such algae blooms are phytoplankton.

Explanation:

It needs nitrogen in the biologically available for the initial synthesis of the organic matter. The phytoplankton in the water is excreted as the ammonia and urea.

Some algae blooms are the results of the excess of the nutrients into the water and the higher concentration of the nutrients in the water caused the increased growth of algae and the green plants.

In the nitrogen fixation, bacteria converted into ammonia and form of the nitrogen which is usable by the plants. It acquires the nitrogen compounds by eating the plants.