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How do temperature, altitude, and salinity affect dissolved oxygen in water?
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Inland water ecosystem
Figure 1: Relationship between the density of pure water and temperature.
In inland water ecosystems, the concentration of dissolved oxygen is significantly influenced by temperature, altitude, and salinity. These three factors share an inverse relationship with the solubility of oxygen in water, meaning that as each of these variables increases, the amount of oxygen that can remain dissolved in the water decreases.1
- Temperature: Oxygen solubility is inversely correlated with temperature. As water temperatures rise, the oxygen content decreases. For example, a shift from 5°C to 35°C can reduce the oxygen content of fresh water by nearly half.12
- Altitude: The availability of dissolved oxygen decreases in parallel with declines in atmospheric pressure at higher altitudes. Because atmospheric pressure is lower at higher elevations, the partial pressure of oxygen is reduced, which limits the amount of gas that can be held in solution.21
- Salinity: The presence of dissolved salts limits the amount of oxygen available in natural waters. As the concentration of salts—such as sodium chloride—increases, the solubility of oxygen decreases. Consequently, saline waters generally hold less dissolved oxygen than fresh water under identical conditions.213