Salinity Protocols

1
Salinity Protocols

• PBL Module
• Portsmouth Public Schools
• Hampton University

2
What is Salinity

• The relative concentration of dissolved salts,
  usually sodium chloride in a given water sample.
• Measured in parts per thousand (ppt or PSU
  Practical Salinity Units)
• Tidal Fresh 0 - 1 ppt, tidal influence
• Oligohaline 2 - 5 ppt (slightly brackish)
• Mesohaline 8 - 15 ppt (brackish)
• Polyhaline 18 ppt and up (salt water)

3
Methods of Determining Salinity

• Evaporation
• Specific Gravity/Density
• Refraction
• Conductivity
• Titration (argentometric method)

4
Evaporation

• Ratio of mass of salts to mass of water and
  salts.
• Expressed in PPT/PSU

5
Specific Gravity/Density

• Use of a hydrometer
• SG of fresh water 1.000
• As salt is added the SG will increase.

S-T-D graph
6
Refraction

• Based upon the refraction index of light passing
  through a prism.
• Refractometer
• Direct reading scale in PPT o/oo.
• Temperature correction

Sample Activity
7
Conductivity

• Pure water is a poor conductor of electricity.
• Dissolved ions of salt increase the conductivity.
• Amount of electrical current is proportional to
  concentration of dissolved ions.
• Conductivity meter
• Salinomenter
• CTD

Click to visit the High Tide website.
8
Titration

• Chemical reaction usually using silver nitrate
• NaCl AgNO3gtgtgtNaNO3 AgCl
• Silver Chromate is color indicator.
• Roughly S (in PPT) 1.80655 x Cl (in PPT)

9
End of Salinity Protocol PPT
10
36.90605 N 76.30511 W
1 m
4 m
6.5 m
Lafayette River Bridge, Norfolk Click on each of
the water sampling bottles to retrieve the water
samples. Read the salinity with the
refractometer. Follow cues to return to lesson.
Back to Refraction
11
Continue your salinity protocols.
Press this button to continue.
12
Lafayette River Bridge 1 meter
20 PPT
22 PPT
25 PPT
27 PPT
Back to the bridge
13
Lafayette River Bridge 4 meters
24 PPT
27 PPT
28 PPT
30 PPT
Back to the bridge
14
Lafayette River Bridge 6.5 meters
26 PPT
28 PPT
31 PPT
33 PPT
Back to the bridge
15
Zowie!

• Right on the nose! Well within our tolerances!

Continue
16
Oh No!

• Think you might have measured a bit too high!
  Try again.

Continue
17
OOPS!

• It appears you are a tad low.

Continue