Dissolved Oxygen and Other Gases

Abstract

Concentrations of atmospheric gases in water at saturation vary with the partial pressures and solubilities of the gases, and the temperature and salinity of the water. Dissolved oxygen is used to illustrate the principles of gas solubility. Concentrations of dissolved oxygen at saturation decrease with greater elevation (lower barometric pressure), higher salinity, and rising temperature. The concentration of dissolved oxygen in water may be expressed in milligrams per liter, but it also can be reported in milliliters per liter, percentage saturation, oxygen tension, or other units. The rate of diffusion of dissolved oxygen into water bodies is related to various factors, but the most important are the concentration of the dissolved oxygen already in the water, the area of contact between the air and water, and the amount of wind-driven or other turbulence in the water. Oxygen will diffuse into the air from oxygen-supersaturated water bodies. Dissolved oxygen is of utmost importance in water quality, because it is essential for aerobic respiration. Absorption of oxygen by fish and other aquatic animals is controlled by the pressure of oxygen in the water rather than the dissolved oxygen concentration in milligrams per liter. Low oxygen pressure can stress or even kill aquatic organisms. Excessive dissolved gas (including oxygen) concentrations in water can lead to gas bubble trauma in fish and other aquatic animals.