PASCO PS-2108 Dissolved Oxygen Sensor - Manual (Page 18)

PASPort Dissolved Oxygen Sensor Model No. PS-2108
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5. Surface Area and Mixing/Turbulence
• The surface area of the water/gas interface may affect the rate at which gas dissolves into
the water, but ultimately, it will not affect the total amount of gas dissolved at static (non-
turbulent) equilibrium. Situations in which turbulence is constant (such as the outfall from
a dam spillway) can host a dynamic equilibrium in which water remains supersaturated at a
given point in the stream.
• Stirring a water sample in a laboratory setting has a drastic effect on the behavior of the
DO probe. The nature of a Clark-type probe is that it consumes oxygen in its immediate
environment (leading to an apparent localized drop in DO level). Stirring the sample,
while taking data, is highly recommended in order to obtain faithful DO readings. It is
crucial to maintain a sufficient flow rate across the membrane of the sensor. Flow of about
1 cm per second is recommended. Do not stir to the point of causing excessive turbulence
in the water.
• Allow the probe to reach equilibrium in experiments that are not conducive to stirring.
There will be an initial drop (in most cases up to 60 seconds) on apparent readings until a
local equilibrium is established.
Citations:
1. WOW. 2003. Water on the Web - Monitoring Minnesota Lakes on the Internet and Training
Water Science Technicians for the Future - A National On-line Curriculum using Advanced
Technologies and Real-Time Data. (http://wow.nrri.umn.edu). University of Minnesota-
Duluth, Duluth, MN 55812
2. Table HY-DO-1 from Globe Dissolved Oxygen Protocol (http://www.globe.gov/tctg/
hydro_prot_do.pdf?sectionId=151)
3. Ambient Water Quality Criteria for Dissolved Oxygen, February, 1997. Water
Management Branch Environment and Lands Headquarters Division, Ministry Of
Environment, Lands and Parks, Canada
4. Hitchman, Michael L.1978. Measurement of Dissolved Oxygen. John Wiley and Sons,
New York. 255 p.
15.0 10.084 9.541 9.027 8.540 8.079 7.642
16.0 9.870 9.344 8.844 8.370 7.922 7.496
17.0 9.665 9.153 8.667 8.207 7.770 7.356
Chlorinity (freshwater)
Temp.
(°C) 0 g/L Cl- 5.0 g/L Cl- 10.0 g/L Cl- 15.0 g/L Cl- 20.0 g/L Cl- 25.0 g/L Cl-