Eutrophication occurs when a body of water receives excess nutrients, inducing massive plant growth that will eventually lead to oxygen depletion.
Excess nutrients are added to the soil from detergent, fertilizer, and sewage. Eventually nutrients drain to a body of water– a lake, river, or ocean. Once in the water, plants flourish from the excess nutrients and create an algae bloom. While excess algae does provide food, it also blocks out all of the light and eventually leads to larger problems. Plants below the algae do not receive light (algae blocks it out) and they die.
Eventually the algae dies and sinks to the bottom where bacteria begin their work. Bacteria are decomposers, and in the process of breaking down organic material they consume oxygen. The algae are no longer producing oxygen because it consumed all of the nutrients and died, therefore bacteria respiration will outpace oxygen production and deplete all oxygen in the water. The fish will suffocate.
The Gulf of Mexico has the largest re-occuring hypoxia zone in the United States. This dead zone (another name for hypoxia zone) can be 6000-7000 square miles. Through mapping techniques we can determine where excess nutrients come from and how they get into the water (everything is connected). Another example that cities, farms, and agriculture have far reaching effects.