+Exploring Dissolved Oxygen

Photos from http://web.vims.edu/bio/sav/index.html

Dissolved Oxygen

Oxygen from the surrounding atmosphere that is absorbed in water and supports aquatic

life.

Dissolved Oxygen

Although water molecules contain oxygen atoms, this oxygen is not accessible to fish and other organisms, because it is locked up in the water molecule.

Instead, air from the surrounding atmosphere dissolves in the water, and it is this dissolved oxygen that supports aquatic life.

Two processes that produce dissolved oxygen are:

1. Photosynthesis: primary producers in aquatic environments generate oxygen through photosynthesis.

2. Solubility of oxygen: oxygen from the surrounding atmosphere dissolves into the water.

Factors that can affect the amount of dissolved oxygen in

water. 1. Fast-flowing water may absorb more

dissolved oxygen than slower-moving water.

2. Organisms in the water that use oxygen for respiration will also deplete oxygen levels.

3. Temperature can change the amount of oxygen that water can hold.

+1. Go to www.dataintheclassroom.org2. Select “Water Quality”.3. Select “Lesson 2”.4. Read and answer the questions on

that page.

+1. Go to www.dataintheclassroom.org2. Select “Water Quality”.3. Select “Get Data”.4. Select “Water Quality” from the list.5. Choose “ACE Basin > Big Bay” from

the list of recording stations.6. Choose “Water Temperature” as the

first parameter and “Dissolved Oxygen” as the optional second parameter.

7. Under “start date,” select Jun. 1, 2007.

8. Select a duration of“1 Day.”9. Select “Graph” selected under

“Specify an output format.”10.Click the “Get Data” button.

Photosynthesis is when plants use sunlight, nutrients, and carbon dioxide to produce food. When during the day should photosynthesis be highest?

Photosynthesis is when plants use sunlight, nutrients, and carbon dioxide to produce food. When during the day should photosynthesis be highest?

Photosynthesis should be greatest during the afternoon, the sunniest part of the day.

Photosynthesis also produces oxygen. When during the day would the most

oxygen be produced?

Photosynthesis also produces oxygen. When during the day would the most

oxygen be produced?

Photosynthesis and oxygen production would also be greatest during the afternoon, the sunniest part of the day.

Does warm soda or cold soda contain more gas?

Does warm soda or cold soda contain more gas?

Cold soda. As temperature increases, the gas molecules have more energy and move faster and out of the soda.

Would you expect warm water to contain more or less dissolved oxygen than cold water?

Would you expect warm water to contain more or less dissolved oxygen than cold water?

Warm water would contain less dissolved oxygen than cold water.

So, during the afternoon of a sunny day, photosynthesis is high, producing lots of oxygen. However, the warm water cannot hold as much oxygen. Why does the dissolved oxygen still rise?

So, during the afternoon of a sunny day, photosynthesis is high, producing lots of oxygen. However, the warm water cannot hold as much oxygen. Why does the dissolved oxygen still rise?

Warm water would contain less dissolved oxygen than cold water.

So, during the afternoon of a sunny day, photosynthesis is high, producing lots of oxygen. However, the warm water cannot hold as much oxygen. Why does the dissolved oxygen still rise? Let’s look at the bay for a year to find out.

+1. Change the duration to Jan, 1, 2007

for “1 year.”2. Select “Graph” selected under “Specify an output format.”3. Click the “Get Data” button.4. Now, you have both graphs on your

desktop. Press F9 to toggle between the two and answer the questions in the PowerPoint.

How would you describe the relationship between temperature and dissolved

oxygen in the two graphs?

In the first graph (one day), dissolved oxygen and water temperature are both high at the same time. In the second graph (one year), they have the opposite relationship: when water temperature is high, dissolved oxygen is low.

What might explain the apparent difference in the relationship of water temperature and dissolved oxygen in the two graphs? (Hint: consider thedifference between the lowest and highest temperatures recorded over one day vs. one year.)

Over one day, the change in water temperature is relatively small (less than 20C). Therefore, the ability of the water to absorb oxygen doesn't change much over that range. Over one year, the water temperature changes at least 200C, which impacts dissolved oxygen levels over time. At this longer time scale, the influence of temperature is more evident.

Over one day, the change in water temperature is relatively small (less than 20C). Therefore, the ability of the water to absorb oxygen doesn't change much over that range. Over one year, the water temperature changes at least 200C, which impacts dissolved oxygen levels over time. At this longer time scale, the influence of temperature is more evident.

How might you explain the change in dissolved oxygen in the first graph (one day)? Hint: Think of the other way that produces dissolved oxygen.

Dissolved oxygen is generated by microorganisms duringphotosynthesis. Just as water temperature is highest in theafternoon when the sun is high, perhaps dissolved oxygen isalso high because there is more sunlight for photosynthesis.

Go back to http://apps.dataintheclassroom.org/water-quality/FormGenerator.aspx

Go to Chesapeake, MD > Otter Point Creek and choose the parameter and dates shown here, on the left. Change the duration to Jan, 1, 2007 for “1 year.” Select “Graph” selected under “Specify an output format.” Click the “Get Data” button. Now, you have three graphs on your desktop. Press F9 to toggle between them.Do you see the same yearly trends?Repeat for other Chesapeake sites.