Excelet

When are dissolved oxygen levels in natural water higher?

summer or winter

What is your prediction?

Let's investigate how temperature influences the amount of

dissolved oxygen, DO, in water at sea level.

We will also examine how atmospheric pressure and salinity

(salt content) influence the amount of dissolved oxygen.

Click on the tabs to navigate.

How does the dissolved oxygen (DO) level vary with temperature?

DO (mg/L) 0

0 14.6 -10 -10

3 13.5 -10 -10 0

6 12.5 -10 -10

9 11.6 -10 -10

12 10.8 -10 -10

15 10.2 -10 -10

18 9.5 -10 -10

21 9.0 -10 -10

24 8.5 -10 -10

27 8.1 -10 -10

30 7.6 -10 -10

33 7.3 -10 -10

36 7.0 -10 -10

These are the maximum soluble or saturation levels of oxygen in freshwater at sea level.

T (oC)

Source of data: Standard Methods for the Examination of Water and Wastewater, 14th ed. (1976)

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0 5 10 15 20 25 30 35 400

2

4

6

8

10

12

14

16f(x) = − 10R² = 0

Temperature, oC

DO

, m

g/L

add linear regression line

lower limit of healthy DO level

Mean monthly dissolved oxygen in stream water.Is this a healthy stream?

Month DO (mg/L)

January 3.22 12.47

February 4.05 12.37

March 7.94 10.61

April 12.89 9.64

May 17.30 8.96

June 20.76 8.63

July 24.06 8.13

August 23.58 7.92

19.61 8.51

October 14.41 9.1

November 8.51 10.37

December 5.75 11.53

What does the plot of DO as

a function of temperature

look like?

Mean data (1985-2005) for Western Branch of the Patuxent River at Water Street in Upper Marlboro

source: http://mddnr.chesapeakebay.net/bay_cond/bay_cond.cfm?param=wt&station=TF12

T (oC)

September

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1 2 3 4 5 6 7 8 9 10 11 120

5

10

15

20

25

30

6

7

8

9

10

11

12

13

Month

Temperature, oC

DO, mg/L

How does the altitude of the body of water influence the DO saturation levels?

at at Altitude = 6000 feet

sea level altitude

DO DO

0 14.6 11.7

3 13.5 10.8

6 12.5 10.0

9 11.6 9.3

12 10.8 8.7

15 10.2 8.2

18 9.5 7.6

21 9.0 7.2

24 8.5 6.8

27 8.1 6.5

30 7.6 6.1

33 7.3 5.9

36 7.0 5.6

760 610

159 128

When the altitude changes, what variable is influenced?

(values are in mm Hg or torr)

For elevations (altitude) in various places in the US

T (oC)

Patm =

Poxygen =

click here

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0 5 10 15 20 25 30 35 400

2

4

6

8

10

12

14

16f(x) = − 10R² = 0

Temperature, oC

DO

, m

g/L

How much gas dissolves in water?25 select a gas

oxygen 1

0.0013 M/atm T (K) = 298

0 0 0 gas 1/kH at T C at 298K kH MM Henry's Law

0.1 0.00013 0.00013 1 oxygen 769.231 1700 769.231 0.0013 32

0.2 0.00026 0.00026 2 hydrogen 1282.05 500 1282.05 0.00078 2

0.3 0.00039 0.00039 3 carbon di 29.41 2400 29.41 0.034 44

0.4 0.00052 0.00052 4 nitrogen 1639.34 1300 1639.34 0.00061 28

0.5 0.00065 0.00065 5 helium 2702.7 230 2702.7 0.00037 4

6 neon 2222.22 490 2222.22 0.00045 20

7 argon 714.28 1300 714.28 0.0014 40

8 carbon mo1052.63 1300 1052.63 0.00095 28

http://en.wikipedia.org/wiki/Henry's_law for gas dissolved in water

tracer 0 0.00027 tracer point

point 0.209 0.00027 0.209 atm

0.209 0 21

0.00027 M

(1.00 atm = 760 torr) 1

8.7 mg/L

NOTE: Henry's Law is expressed in a variety of ways that change the value and units of the Henry's law

independent variable. For a good discussion, see -http://en.wikipedia.org/wiki/Henry's_law

T (oC) =

kH =

Pgas (atm) Cgas (M)

Cgas = kHPgas

Pgas =

Cgas =

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constant, kH, so beware when you see it somewhere else. Here it is in the form where P is the

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0002717

Pgas

Cgas

Pgas

Cgas

line for oxygen at 298K for comparison

How does the salinity of the body of water influence the DO saturation levels?

salinity = 0 g/kg (ppt)

freshwater saltwater freshwater

DO DO

0 14.6 14.6 0.09

3 13.5 13.5 0.08018

6 12.5 12.5 0.07391

9 11.6 11.6 0.06697

12 10.8 10.8 0.06104

15 10.2 10.2 0.05602

18 9.5 9.5 0.05201

21 9.0 9.0 0.04854

24 8.5 8.5 0.0458

27 8.1 8.1 0.04361

Seawater has a typical salinity of 33 g/kg. Where as estuaries vary from freshwater to 33g/kg.

T (oC)

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0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Temperature, oC

DO

, m

g/L

Assess your knowledge:

1. Summarize how temperature, altitude, and salinity influence dissolved oxygen levels.

2. All of this is based on the Earth's present level of oxygen in air at 20.9%. Over geological

time the percentage of oxygen has changed. Levels may have varied from 12% to 30% over

the last 600 million year. How would this change influence the level of dissolved oxygen?

3. When you start to warm a container of water, bubbles form on the container walls. Why?

What is the composition of the gas in the bubbles?

4. Explain the level of DO in the

world oceans. This is the annual

average for 2005 shown to the right.

5. Death Valley in Inyo, CA has an altitude

of -282 ft. How would its DO saturation

levels compare to values at sea level?

http://www.nodc.noaa.gov/cgi-bin/OC5/WOA05F/woa05f.pl

Sinex 2007