What term describes an aquatic system that lacks dissolved oxygen?

The term that best describes an aquatic system that lacks dissolved oxygen is anaerobic. In anaerobic conditions, the environment does not support aerobic respiration, which relies on oxygen. This can occur in situations where organic matter decomposes in water without sufficient oxygen, leading to a state where aerobic organisms cannot survive.

Understanding anaerobic conditions is crucial in aquatic ecosystems, as it impacts the types of organisms that can thrive there, as well as the overall health of the water body. This is contrasted with aerobic conditions, where oxygen is present and supports a variety of life forms. The terms hypoxic and oxic are related but indicate different levels of dissolved oxygen; hypoxic refers to low, but not completely absent, levels of oxygen, while oxic indicates healthy levels of dissolved oxygen that support diverse aquatic life.