Turbidity

TurbidityWalker D. Wright-Moore

Chem 576

12/1/09

What Is Turbidity?• Turbidity is a key measure of water quality and clarity.• Turbidity is the cloudiness or haziness in the water due to

suspended solids.• Causes:

• Land disruption• Effluent discharge• Mineral runoff• Heavy rains• Algae blooms

http://en.wikipedia.org/wiki/Turbidity

Why Measure Turbidity?

• Very important for water treatment.• High turbidity levels have been linked to high levels

of viruses and bacteria.• NC state levels are 50 NTU for fresh water and 25

NTU for tidal saltwater (http://www.epa.gov/safewater/)

• High turbidity can limit the amount of light penetration in the water column:• Effects photosynthesis- low oxygen levels• Sight feeding fish

How We Measure Turbidity:

• Methods: Secchi disc and nephelometers.• Nephelometers:• Standards must be used to calibrate the

instrument.• A source beam is passed through the water

sample and a detector measures the light scattered or reflected.

• Amount of scattering is proportional to turbidity. • Units used in the United States are Nephelometric

Turbidity Untis (NTU). Also seen as FTU.

www.uncwil.edu/cmsr/aquaticecelogy/lcfrp/

M18 M23 M35 M42 M54 M61 HB0

2

4

6

8

10

12

14

16

Surface Turbidity: Cruise 1, Cruise 2 and LCFRP 9 Yr Avg.

cruise 1LCFRP Sept 9 yr avg.cruise 2LCFRP Oct 9 yr avg.

Surface Turbidity compared to Class Averages 02, 04, 06, 07

M18 M23 M35 M42 M54 M61 HB0

1

2

3

4

5

6

7

8

9

10

Cruise 1 vs Class Avg

cruise 1cruise 1 class avg

SITE

Turb

idity

(N

TU)

M18 M23 M35 M42 M54 M61 HB0

2

4

6

8

10

12

14

16

18

20

Cruise 2 vs Class Avg

cruise 2 cruise 2 class avg

SITE

Turb

idity

(N

TU)

http://www.cormp.org

*Red line: Daily Average Discharge is calculated based on the discharge data collected since 1969-09-01

Salinity: Cruise 1 vs Cruise 2

M18 M23 M35 M42 M54 M61 HB0

5

10

15

20

25

30

35

Cruise 1Cruise 2

Salin

ity (

PSU

)

Salinity vs TurbidityCruise 1

0 5 10 15 20 25 30 350

5

10

15

20

25

30

35

40

Deep TurbidityLinear (Deep Turbidity)Surface TurbidityLinear (Surface Turbidity)

Salinity (PSU)

Tur

bidi

ty (

NTU

)

Cruise 2

5 10 15 20 25 300

5

10

15

20

25

Deep TurbidityLinear (Deep Turbidity)Surface TurbidityLinear (Sur-face Tur-bidity)

Salinity (PSU)

Turb

idity

(N

TU)

Deep Turbidity: Cruise 1 vs Cruise 2

M18 M23 M35 M42 M54 M61 HB0

5

10

15

20

25

30

35

40

Deep Turbidity: Cruise 1 vs Cruise 2

cruise 1cruise 2

SITE

Turb

idity

(N

TU)

Deep Turbidity compared to Class Averages 02, 04, 06, 07

M18 M23 M35 M42 M54 M61 HB0

5

10

15

20

25

30

35

Cruise 2 Deep vs Class Avg

cruise 2cruise 2 class avg

SITE

Turb

idity

(N

TU)

M18M23M35M42M54M61 HB0

5

10

15

20

25

30

35

40

Cruise 1 Deep vs Class Avg

cruise 1cruise 1 class avg

SITE

Turb

idity

(N

TU)

Cruise 1:Turbidity vs Kd

5 5.5 6 6.5 7 7.5 8 8.50

0.5

1

1.5

2

2.5

3

Surface TurbidityLinear (Surface Turbidity)

Turbidity (NTU)

Kd

Cruise 2:Turbidity vs Kd

2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.50

0.5

1

1.5

2

2.5

3

1.551.43

1.791.95

2.42.46 2.46

Surface TurbidityLinear (Surface Turbidity)Linear (Surface Turbidity)

Turbidity (NTU)

Kd

*Ignore trendline*

Conclusions:• River discharge could be an indicator of turbidity.• Cape fear river discharge in September, cruise 1, was slightly higher than

October, cruise 2, and both were lower than the past lcfrp average data for those months except surface turbidity at M23 and M35.

• Cruise 1 and 2 surface turbidity showed little correlation with changing salinity, but turbidity did seem to increase with decreasing salinity in the deep water samples.

• It is possible that deep turbidity values could get skewed due to the sampling equipment hitting the bottom and re-suspending bottom material

• Increasing turbidity should correlate with increasing Kd, and maybe some correlation to this affect can be seen. Kd is also influenced by DOC.