Turbidity

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Turbidity
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What is Turbidity?

• A measure of water clarity
• The murkier the water, the higher the turbidity.
• Turbidity reduces the transmission of light into
  water.
• Turbidity increases as a result of suspended
  solids in the water.

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Sources of Turbidity

• Phytoplankton blooms
• Soil erosion
• Waste discharge
• Urban runoff
• Abundant bottom feeders

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Why is Turbidity Important?

• Suspended particles diffuse sunlight and absorb
  heat.
• As temperature increases, DO decreases.
• Suspended solids can clog fish gills
• Less light is available for photosynthesis.
• As sediment settles, gravel beds become fouled.

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How is Turbidity Measured?

• Secchi disk
• Measures water transparency
• Measures depth at which disk is no longer visible
• Useful for deep water

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Turbidity in the lab and field

• Turbidimeter
• optical device that measures scattering of light
  (most accurate)
• Measure in NTU (nephelometric turbidity units) or
  JTU (Jackson turbidity units)

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What is the Turbidity of our Water?

• 5 NTUs maximum contamination level allowed
  (MCL)
• 0.45 NTU highest average turbidity from a local
  well
• 0.15 NTU highest level found at Del Valle Water
  Treatment Plant

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Typical Turbidity Data
Water Source Turbidity Level
Water bodies with sparse plant and animal life 0 JTU
Drinking water lt0.5 JTU
Typical groundwater lt1.0 JTU
Water bodies with moderate plant and animal life 1 - 8 JTU
Water bodies with large plumes of planktonic life 10 - 30 JTU
Muddy water or winter storm flows in rivers 20 - 50 JTU
Water Quality Testing and Monitoring Program for
Middle Schools and High Schools. San Diego
County Water Authority.
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So what?

• Increase in turbidity in reservoirs in
  southwestern U.S.
• Increase in turbidity in Delta waters during dry
  years
• Degrades drinking water quality.
• Water treatment costs increase.
• Decreases light penetration in water.
• Can clog gills of fish.

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Conductivity
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What is Conductivity?

• Conductivity is the measure of waters ability to
  conduct an electric current.
• Estimates amount of total dissolved minerals
  (ions).

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Conductivity in water

• Dissolved salts (ions) conduct electrical current
  in water.
• Absolutely pure water is a poor electrical
  conductor.

http//www.humboldt.edu/dp6/chem110/cond/cond.htm
l
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How do we measure Conductivity?

• Test with a Conductivity meter
• Measured in Siemens or mhos/cm

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Conductivity Units

• Mhos is ohms backwards! (Mhos is the reciprocal
  of ohms if you have to know)
• So.ohms is a measure of the resistance to a
  current.
• The less the resistance, the greater the
  conductivity.
• Conductivity in drinking water is low, so we use
  µmhos/cm or 1 x 10-6 mhos/cm!
• Units are sometimes expressed as microsiemens
  (µS).

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Conductivity and Turbidity Demo

• SEE HANDOUT
• Use of lightbulb as class demo
• Use of conductivity meter
• Use of probeware
• Kit Secchi disk

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Some Conductivity Data
Water Type Conductivity (µmhos/cm)
Distilled Water 0.5 - 3.0
Melted snow 2 - 42
Potable water in U.S. 30 - 1500
Irrigation Supply Water lt 750
Water Source Salinity (g/L)
Sea water 33 - 37
Salton Sea 44
Mono Lake 90
http//www.swrcb.ca.gov/nps/docs/Cond_sal.doc
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So What?

• Increased concentration of salts increases the
  conductivity
• Salts cannot be filtered out
• Higher conductivity can.
• Foul irrigation water (leads to high salinity
  soils)
• Kill wildlife
• Create water shortages

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Salt water and cells

• Salt water is hypertonic to the cells of some
  plants
• This causes plants to wilt and possibly die

http//www.cofc.edu/zaninm/packet_two_files/image
024.jpg
http//www.encyclopedia.com/html/section/osmosis_B
iologicalImportanceofOsmosis.asp