A key characteristic of aquatic dead zones is . A key characteristic of aquatic dead zones is . a high concentration of urban development a low concentration of oxygen low concentrations of nitrogen and phosphorus a lack of water a low concentration of keystone species

The correct answer is "low concentration of oxygen".

Explanation:

One of the key characteristic of aquatic dead zones is its low concentration of oxygen. Aquatic dead zones are classified into this category for being hypoxic, condition that do not support the growth of most marine life. Most aquatic dead zones are in these conditions because of a high content of nutrient pollution caused by human activities.