Chapter 11, Problem 1CR

To determine

The precise nature and the reason for the formation of the Gulf of Mexico’s annual dead zone.

Answer to Problem 1CR

The annual dead zone of the Gulf of Mexico contains a large volume of water with low dissolved oxygen content and cannot sustain animal marine life. The annual dead zone forms due to the depletion of most of the dissolved oxygen in the Gulf’s bottom layer of water.

Explanation of Solution

The Gulf of Mexico’s annual dead zone contains a massive volume of water with low dissolved oxygen content (below 2 parts per million). This condition is responsible for little or no animal marine life in the dead zone. The low dissolved-oxygen levels suffocate bottom-dwelling-fish, crabs, oysters, and shrimps and drive away faster-swimming marine animals.

During spring and summer, large quantities of crop fertilizers (mostly nitrates and phosphates) flow into the Mississippi River and get collected in the northern Gulf of Mexico. This excess of plant nutrients results in the explosive growth of phytoplankton that eventually dies and sinks in the bottom of the water. The dead organisms get decomposed by oxygen-consuming bacteria and cause depletion of most of the dissolved oxygen in the Gulf’s bottom. The resulting volume of water containing low dissolved-oxygen content is termed as a dead zone.