What factor directly affects the quantity of oxygen that can be dissolved in water?

The quantity of oxygen that can be dissolved in water is primarily influenced by temperature. As water temperature increases, the solubility of oxygen decreases. This relationship is rooted in the physical chemistry of gases, where warmer temperatures provide more kinetic energy to water molecules, thereby allowing oxygen molecules to escape from the water to the atmosphere. Conversely, cooler water can hold more dissolved oxygen, making temperature a crucial factor in aquatic environments, especially in the context of water treatment and aquatic life sustainability.

While factors such as pressure, pH level, and salinity also play roles in the overall dynamics of dissolved gases, they do not have the same direct and pronounced effect on the solubility of oxygen as temperature does. For instance, increasing pressure would enhance the solubility of gases in water, but typically, in natural aquatic systems under typical atmospheric conditions, temperature remains the most significant factor affecting oxygen levels in water.