When fertilizers run off farmland into streams and ponds, the nitrogen content of the water increases. this can lead to rapid growth of algae in a process called eutrophication. how can this process affect other organisms in the water? the water becomes better able to support aerobic organisms. oxygen is used up as algae is decomposed, reducing the amount available to other organisms. the algae provide food for fishes and other organisms, leading to decreased algae populations. the extra nitrogen provides additional food for the other organisms, increasing their population.

The correct answer is 'Oxygen is used up as algae is decomposed, reducing the amount available to other organisms.' The additional nutrients in the water will result in an algal bloom. These algae will result in drastic oxygen fluctuation, from oxygen rich conditions during the day as algae photosynthesize, to anoxic conditions during the night when the algae respire. However, the algal bloom will eventually deplete the available nutrients, resulting in a vast algal die off. The decomposing algae result in anoxic conditions, and the effects are sometimes very obvious, with fish gasping for breath and dying.