Rain dissolves fertilizer in the soil. Runoff carries it away. The fertilizer ends up in bodies of water, from ponds to oceans. Nitrogen is a fertilizer in the water. Since there is a lot of nitrogen, it causes algae to grow out of control. Pictured below is a pond covered with algae ( Figure below ). Algae use up carbon dioxide in the water. After the algae die, decomposers break down the dead tissue. The decomposers use up all the oxygen in the water. This creates a dead zone. A dead zone is an area in a body of water where nothing grows because there is too little oxygen. There is a large dead zone in the Gulf of Mexico ( Figure below ). The U.S. states outlined on the map have rivers that drain into the Gulf of Mexico. The rivers drain vast agricultural lands. The water carries fertilizer from these areas into the Gulf.
Jim and Greg are brothers who both run their own farms, but they rarely see each other due to them living in different states. Greg runs a farm in Texas where he rarely sees rain so he spends much of his day watering his crops. Jim lives in Illinois where it rains much more regularly so he has more time to spend dealing with his farm animals instead of watering his plants. Both men intentionally purchased their farms next to lakes since they have always loved fishing during their free time. The brothers are currently planning a fishing trip together, but they are just debating which lake to travel to.

Will Jim's lake have more or less carbon dioxide than Greg's?