Yes, PButter that is an excellent point to bring up, higher saline concentration does reduce the amount of dissolved oxygen the water can hold.
Oxygen is soluble in water and the oxygen that is dissolved in water (DO) will equilibrate with the oxygen in atmosphere. Oxygen tends to be less soluble as temperature increases, with warmer water containing less oxygen then colder water. Water salinity also has an effect on dissolved oxygen levels, with higher saline reducing the availability of oxygen in the water.
The dissolved oxygen of fresh water at sea level will range from 15 mg/l at 0° C to 8mg/l at 25° C. Concentrations of unpolluted fresh water will be close to 10 mg/l at 15° C.
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