Oxic

Oxic is an adjective used in science to describe environments, conditions, or processes that contain detectable levels of dissolved oxygen or involve oxygen as a reactant. The term is most often contrasted with anoxic (lacking oxygen) and hypoxic (low oxygen). Oxic conditions are typically found in well-ventilated surface waters, well-aerated soils, and many industrial or engineered systems where aeration supplies oxygen for biological activity.

In aquatic settings, the oxic zone is the layer of water or sediment where dissolved oxygen supports aerobic organisms and processes. Oxygen concentration can be measured in mg/L or as a percentage of saturation; thresholds for “oxic” vary by discipline but generally exceed the minimum needed for aerobic respiration. Deeper layers or sediments can be anoxic, where oxygen is depleted and anaerobic metabolism prevails.

In microbiology and biogeochemistry, oxic respiration uses molecular oxygen as the terminal electron acceptor. Where oxic conditions shift to anoxic, organisms may switch to anaerobic respiration or fermentation, altering nutrient cycling and metal solubility. In soils, oxic conditions promote oxidation of reduced minerals (for example, iron(II) to iron(III)) and affect nutrient availability.

Industrial and wastewater treatment practices deliberately maintain oxic conditions through aeration to support nitrification and organic matter breakdown. Fluctuations between oxic and anoxic states are exploited in processes such as enhanced biological phosphorus removal and cyclically aerated reactors.