1. Turbidity

2. 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.

3. Sources of Turbidity Phytoplankton blooms Soil erosion Waste discharge
Urban runoff
Abundant bottom feeders

4. 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.

5. How is Turbidity Measured?
Secchi disk
Measures water transparency
Measures depth at which disk is no longer visible
Useful for deep water

6. 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)

7. What is the Turbidity of our Water?
5 NTU’s = 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

8. Typical Turbidity Data
Water Source
Turbidity Level
Water bodies with sparse plant and animal life
0 JTU
Drinking water
<0.5 JTU
Typical groundwater
<1.0 JTU
Water bodies with moderate plant and animal life
1 - 8 JTU
Water bodies with large plumes of planktonic life
JTU
Muddy water or winter storm flows in rivers
JTU
Water Quality Testing and Monitoring Program for Middle Schools and High Schools. San Diego County Water Authority.

9. So what? Degrades drinking water quality.
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.

10. Conductivity

11. What is Conductivity?
Conductivity is the measure of water’s ability to conduct an electric current.
Estimates amount of total dissolved minerals (ions).

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

13. How do we measure Conductivity?
Test with a Conductivity meter
Measured in Siemens or mhos/cm

14. 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).

15. Conductivity and Turbidity Demo
SEE HANDOUT
Use of lightbulb as class demo
Use of conductivity meter
Use of probeware
Kit Secchi disk

16. Some Conductivity Data
Water Type
Conductivity
(µmhos/cm)
Distilled Water
Melted snow
2 - 42
Potable water in U.S.
Irrigation Supply Water
< 750
Water Source
Salinity
(g/L)
Sea water
Salton Sea 44
Mono Lake 90

17. 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

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