AP BIOLOGY

Detailed explanation-1: -Dead zones develop when fertilizers and nutrients from farmland drain into oceans or lakes, creating an algae bonanza that eventually dies and decomposes. As the algae decomposes, it depletes the waters of oxygen, suffocating species that live in the area.

Detailed explanation-2: -Nitrogen and phosphorous from agricultural runoff are the primary culprits, but sewage, vehicular and industrial emissions and even natural factors also play a role in the development of dead zones.

Detailed explanation-3: -Dead zones occur because of a process called eutrophication, which happens when a body of water gets too many nutrients, such as phosphorus and nitrogen. At normal levels, these nutrients feed the growth of an organism called cyanobacteria, or blue-green algae.

Detailed explanation-4: -Nutrient run-off triggers dead zones (Read about a large dead zone in the Baltic Sea.) The largest dead zone in the world lies in the Arabian Sea, covering almost the entire 63, 700-square mile Gulf of Oman. The second largest sits in the Gulf of Mexico in the United States, averaging almost 6, 000 square miles in size.