The yellow substance absorption was measured as UV-VIS transparency of the filtered sample in vitro. According to procedure recommended by Reuter at al. (1986 ), samples were collected with use of the Nansen Bottle and then were filtered on board with the use of the Sartorius 0.2 mm cellulose membrane filters. Filtered water was stored in the dark cool condition in the brown glass bottles of 200 ml capacity. The amount of 400 ml of 0.5 M HgCl2 was added to prevent bacterial growth and degradation of DOM. The transparency of the samples was measured with use of the double beam Perkins Elmer spectrophotometer in the 10 cm quartz cell in the spectral range 300- 700 nm. The 10 cm quartz cell filled with double destilled water was used as the reference. The transparency in absorbance units A₁₀(lambda) was transformed into absorption coefficient which obey Lambert-Berr law with use of the following relation:

This procedure was applied to minimise the loss of the absorption properties of DOM. The effect of time, bacterial degradation, bacterial growth, and light on absorption properties of DOM has been assessed by Diebel-Langohr at. al. (1986).

References:

1. Diebel-Langohr D., Doerffer R., Reuter R., Dörre F., Hengstermann T., 1986, Long term stability of Gelbstoff concerning its optical properties. in The influence of yellow substances on remote Sensing of sea water constituents from Space. Report of ESA Contract No. RFQ 3-5060/84/NL/MD, GKSS Research Centre Geesthacht
2. Reuter R., Albers W., Brandt K., Diebel-Langohr D., Doerffer R., Dörre F., Hengstermann T., 1986, Ground truth techniques and procedures for Gelbstoff measurements. in The influence of yellow substances on remote Sensing of sea water constituents from Space. Report of ESA Contract No. RFQ 3-5060/84/NL/MD, GKSS Research Centre Geesthacht