Dissolved Oxygen Levels Investigating the Solubility of Gases

Solubility of Oxygen Gas in Water Check out this solubility curve for oxygen gas in water. What is the solubility at 20°C? At 40°C? 0.044 g/kg of water 0.031 g/kg of water What can you conclude about the solubility of oxygen as temperature goes up? Solubility decreases.

Yes, it is. As temperature increases, solubility decreases. Is this true for other gases? CH4 = methane, CO = carbon monoxide, He = helium Carbon dioxide Yes, it is. As temperature increases, solubility decreases.

Let’s do a demonstration! What can we conclude about the solubility of gases in water with respect to temperature? THAT AS THE TEMPERATURE INCREASES, SOLUBILITY OF GASES DECREASES. Let’s do a demonstration! I need two assistants.

How does the solubility of gases compare with solids? Compare at 30 °C

Another solubility factor is pressure How does pressure affect solubility? When you open a can of soda, what happens to the pressure of the soda? IT IMMEDIATELY DECREASES What happens to the gas that was dissolved in the soda? IT COMES OUT OF THE SOLUTION

Could temperature have an affect on the fish kill? We just learned that temperature affects how much oxygen gas can dissolve in water, here the Snake River. Different aquatic life forms have different requirements for the concentration of dissolved oxygen for survival. The dissolved oxygen requirements are different in summer and winter.

Dissolved oxygen requirements for fish by season Fish species Summer (mg/L) Winter (mg/L) Pike 6.0 3.1 Black crappie 5.5 4.7 Yellow perch 4.2 1.5 Green sunfish 3.3 3.5 Black bullhead 1.2 Trout 4.1 ? Salmon 3.9

Dissolved oxygen (mg liter-1) concentrations required by different Chesapeake Bay species and communities (Source: EPA)

How does temperature affect fish internally? As temperature increases, there is _____ dissolved oxygen in water for fish to breathe! BUT, as temperature goes up, so does the fish’s body temperature (it is a cold-blooded creature) and its metabolism increases. This means it eats more, swims more and requires _____ dissolved oxygen to breathe.

Maximum water temperature (24 hour exposure) Water temperatures can get too high for fish, as in summer when long stretches of hot weather lead to too little dissolved oxygen in the water and large fish kills. Maximum water temperature (24 hour exposure) °C °F Trout 24 75 Catfish 35 95 Lake herring 25 77 Largemouth bass 34 93 Northern pike 30 86

What human practices can lead to higher temperatures in rivers? Industries that use natural bodies of water to cool their heat-producing processes, such as electrical power generation.

Can there be too much oxygen for fish? Yes! When the total amount of dissolved gases—oxygen and nitrogen—reaches 110% to 124% of saturation (supersaturation), fish can develop GAS BUBBLE TRAUMA. This situation can occur at the base of a dam or hydro-electric project where released water forms “froth.”

Gas Bubble Trauma The supersaturated gases cause bubbles of oxygen and nitrogen to form in the fish’s blood and tissues. The fish may be able to use some of the oxygen, but the nitrogen bubbles block blood flow within the fish, leading to death. This is related to the condition called “the bends” which affects scuba divers if they ascend too rapidly from deep water.