What can low dissolved oxygen (DO) levels in water indicate?

Low dissolved oxygen (DO) levels in water can indicate high pollution or contamination. When pollutants, especially organic matter, are present in significant quantities, they can lead to a heightened demand for oxygen as microorganisms break down this organic material. This process, known as aerobic decomposition, consumes oxygen, resulting in decreased DO levels. Consequently, low DO is often a sign of impaired water quality, which can adversely affect aquatic life that relies on sufficient oxygen levels for survival.

High nutrient levels can contribute to increased algal blooms, which can ultimately deplete oxygen in the water when the algae die and decompose, but the direct connection is more aligned with the aspect of pollution and contamination. Elevated water temperature can affect oxygen solubility, which might lead to lower DO levels, but it is not solely indicative of pollution. Good water quality is associated with adequate DO levels, typically enough to support aquatic organisms. Thus, low DO levels primarily highlight issues related to pollution and water quality degradation.