HT+Task+2

=__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? Fish have something like a filtration system called gills, it takes the oxygen atoms out of the water and pushes the water back out

2.) How does oxygen enter the water supply? When water is formed it takes two hydrogen and one oxygen atoms to make

3.) What human factors effect the levels of dissolved oxygen? If we dump or litter into the water supply, it can make the water more or less acidic

4.) What natural factors effect the levels of dissolved oxygen? Increasing the temperature of the water, water at high altitudes, slow moving water, and water with high levels of plant life.

5.) Predict: If Mashamoquet were a healthy ecosystem, what level of dissolved oxygen might you expect to find there? A good level of dissolved oxygen is 7 - 11 mg/L. This level is good enough for most stream fish to live. 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 isn't enough for most animals to survive.

__**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: Tap water

List the level of dissolved oxygen. 4 was the first reading 6 was after for the second part of the lab

**Analysis** Is the level of dissolved oxygen for your sample a safe and a healthy level for fish and other aquatic organisms? Yes because a level of 4-7 mg/L is good for most aquatic animals and ours was around that.

**Conclusion** 1.) Do you think you have may encountered any errors in the lab? If so, describe them. We got confused and didn't mix the chemicals the right way, based on reading the procedure wrong.

2.) How might you overcome those errors next time you are collecting this data? Read the procedure more carefully and take our time.

Please review your prelab. We get oxygen from the oxygen in the air, not in the water molecule Graded.