Dissolved Oxygen and Temperature
Name: Margaret C.
Why does cold water contain more dissolved oxygen than warmer water?
If one looks at the solubility curve for oxygen gas, plotted as milligrams of oxygen
dissolved per 1000 g of water, the solubility of oxygen at 0 degrees C is about
twice its solubility at 30 degrees C. As the temperature of the water goes up, the
lower the concentration of dissolved oxygen gas. Simply stated, the water
temperature helps determine the maximum amount of oxygen gas that water can
dissolve. This dissolved oxygen concentration, in turn, helps determine water's
ability to support oxygen-consuming creatures. Water temperature also effects the
amount of oxygen actually needed by aquatic organisms. A 10 degree temperature
rise roughly doubles the rate or speeds of many chemical reactions in the water
environment. Cooling a system down by 10 degrees slows down the rates of such
reactions by a similar factor.
During warm summer months, competition among water inhabitants for dissolved oxygen can become quite severe. With rising water temperatures, bacteria and fish require more oxygen. But warmer water is unable to dissolve as much oxygen gas. After a long stretch of hot summer days, some streams experience large fish kills, in which many fish suffocate.
I hope that this helps.
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Update: June 2012