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=__Dissolved Oxygen Test__=

Have you ever wondered how fish breathe in water? They do not use the oxygen that is found in the molecule (H2O). Instead, fish and other aquatic animals use oxygen gas, that has been dissolved in water, to breathe. This oxygen gas is referred to as dissolved oxygen and it is very important in maintaining the balance of the ecosystem.

Dissolved oxygen enters the water in a couple ways. One way is through the process of photosynthesis in aquatic plant life. The other is through diffusion of oxygen in the air at the surface. Ideally a good level of dissolved oxygen is 7 - 11 mg/L. This level is good enough for most stream fish to thrive. A level of 4-7 mg/L is good for most pond animals; 2 -4mg/L is good for few species of aquatic animals. Anything less than 2mg/L is not enough for most animals to survive.

Factors that effect the levels of dissolved oxygen (DO for short) are human factors and naturally occurring factors. Human factors that effect the levels of dissolved oxygen are the addition of sewage wastes and fertilizers. The addition of waste such as sewage contains organisms that use up the oxygen. The addition of nutrients (eutrophication) causes the plants and algae to rapidly grow and die off, due to over crowding This brings in high levels of bacteria which use up the oxygen. Natural factors which effect the level of dissolved oxygen are increasing the temperature of the water, water at high altitudes, slow moving water, and water with high levels of plant life.

__**Prelab**__ 1.) Where do aquatic organisms get the oxygen they need to breathe? they have like a filtration system called there gills were it takes the water and gets the oxygen out of the water so they can breath  2.) How does oxygen enter the water supply? when water is formed it takes two hydrogen and one oxygen atomes to make to that is how oxygen enters the water suply 3.) What human factors effect the levels of dissolved oxygen? if we litter or dump something into the water suply that isn't suppose to be there than it can make the water more or less acidic  4.) What natural factors effect the levels of dissolved oxygen?

5.) Predict: If Mashamoquet were a healthy ecosystem, what level of dissolved oxygen might you expect to find there?

__**Procedure and Materials**__ Please see La Motte: Dissolved Oxygen Test kit Instructions.

Please be aware of the safety warnings for Manganous Sulfate Solution, Alkaline Potassium Iodide Azide, Sodium Thiosulfate, and Sulfamic acid.

- Identify any safety precautions you should take or any warnings that the chemicals you are using may have. Be aware of how these chemicals may cause you harm

__**Data**__

Identify where you obtained your experimental sample from:

List the level of dissolved oxygen.

**Analysis** Is the level of dissolved oxygen for your sample a safe and a healthy level for fish and other aquatic organisms?

**Conclusion** 1.) Do you think you have may encountered any errors in the lab? If so, describe them.

2.) How might you overcome those errors next time you are collecting this data?