IOCS• Rüdiger Röttgers • 21.05.2013 1

Light absorption in turbid waters

Rüdiger Röttgers, Kerstin Heymann,

Hajo Krasemann

Determination of suspended matter concentration

problematic issues:

- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;

Stavn et al. 2009) and loss of filter material

- methodology in sea water:

1) rinsing of the rim after filtration

2) collection of high sample masses to reduce the rel. effect of the offset

3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset

- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)

IOCS• Rüdiger Röttgers • 21.05.2013 2

Determination of suspended matter concentration

problematic issues:

- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;

Stavn et al. 2009) and loss of filter material

- methodology in sea water:

1) rinsing of the rim after filtration

2) collection of high sample masses to reduce the rel. effect of the offset

3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset

- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)

IOCS• Rüdiger Röttgers • 21.05.2013 3

Determination of suspended matter concentration

problematic issues:

- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;

Stavn et al. 2009) and loss of filter material

- methodology in sea water:

1) rinsing of the rim after filtration

2) collection of high sample masses to reduce the rel. effect of the offset

3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset

- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)

IOCS• Rüdiger Röttgers • 21.05.2013 4

Determination of suspended matter concentration

problematic issues:

- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;

Stavn et al. 2009) and loss of filter material

- methodology in sea water:

1) rinsing of the rim after filtration

2) collection of high sample masses to reduce the rel. effect of the offset

3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset

- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)

IOCS• Rüdiger Röttgers • 21.05.2013 5

Determination of suspended matter concentration

problematic issues:

- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;

Stavn et al. 2009) and loss of filter material

- methodology in sea water:

1) rinsing of the rim after filtration

2) collection of high sample masses to reduce the rel. effect of the offset

3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset

- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)

IOCS• Rüdiger Röttgers • 21.05.2013 6

Determination of suspended matter concentration

problematic issues:

- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;

Stavn et al. 2009) and loss of filter material

- methodology in sea water:

1) rinsing of the rim after filtration

2) collection of high sample masses to reduce the rel. effect of the offset

3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset

- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)

IOCS• Rüdiger Röttgers • 21.05.2013 7

Determination of suspended matter concentration

problematic issues:

- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;

Stavn et al. 2009) and loss of filter material

- methodology in sea water:

1) rinsing of the rim after filtration

2) collection of high sample masses to reduce the rel. effect of the offset

3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset

- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)

IOCS• Rüdiger Röttgers • 21.05.2013 8

-0.5 mg

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40

rel.

err

or

[%]

mass on filter [mg]

Determination of suspended matter concentration

problematic issues:

- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;

Stavn et al. 2009) and loss of filter material

- methodology in sea water:

1) rinsing of the rim after filtration

2) collection of high sample masses to reduce the rel. effect of the offset

3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset

- problem: process filter offset highly variable: -0.1 – 1 mg, mean: 0.5 mg (n=150)

- real sample filter offset varies even more: -4 – +7 mg, mean: 1 mg (n=380), inducing error of >100 %

to reach error of <15%, >20 mg have to be collected

IOCS• Rüdiger Röttgers • 21.05.2013 9

Light absorption in turbid waters

- what are the dominating absorbing water constituents in turbid waters?

- how large is the absorption in the NIR/SWIR region?

- what absorbs light in the NIR/SWIR region?

IOCS• Rüdiger Röttgers • 21.05.2013 10

particulate absorption, ap

IOCS• Rüdiger Röttgers • 21.05.2013 11

bleached particulate absorption

IOCS• Rüdiger Röttgers • 21.05.2013 12

mass-specific particulate absorption, ap

IOCS• Rüdiger Röttgers • 21.05.2013 13

y = 0,0109x - 0,023 R² = 0,980

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 20 40 60 80 100 120 140 160 180

a8

50

nm [1

/m]

TSM [mg/L]

River Elbe

Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 14

Absorption of dried matter

To reduce influence by water absorption filter pad samples were dried at ca. 60 °C.

German Bight, dried samples

Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 15

Absorption of dried non-algal matter

German Bight, dried samples

from Graham R. Hunt, 1977

Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 16

NIR/SWIR Absorption of Minerals

Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 17

NIR/SWIR Absorption of Minerals

from Graham R. Hunt, 1977

Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 18

NIR/SWIR Absorption of Minerals

from Graham R. Hunt, 1977

reflectance studies

Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 19

NIR/SWIR Absorption of Minerals vs. Particle Size

Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 20

NIR/SWIR Absorption of Minerals vs. Particle Size

Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 21

Summary / Conclusions

•absorption in turbid water is dominated by non-algal matter

•NIR/SWIR absorption is substantial in natural samples, a800nm >1 - 25 % of the a442nm and can be

measured exactly

• absorption in NIR/SWIR is dominated by minerals, mainly from water structures in the mineral

• absorption by organic detritus has still to be determined, as separation of inorganic and organic

part remains difficult

• NIR/SWIR absorption might be used for identification of mineral types in suspended matter

• dependencies of absorption on particle size can be determined → imaginary part of the complex

refractive index