The Oder Estuary - IOW

Iopt values (Figure 2.3) were adopted after STIGEBRANDT & WULFF (1987). Iopt changing through
seasons accounts for occurrence of different phytoplankton species which are adapted to various
light conditions. The Iopt values are similar to the values from measurements given by RENK et al.
(2001) for the Vistula Lagoon which is a similar type of a water body with respect to the light
climate as the Szczecin Lagoon.
W/m2/d
160
140
120
100
80
60
40
20
0
2.3.5 Light attenuation with depth
The intensity of light diminishes with depth in an exponential way:
-Kd x depth
PARwater = PARatmosphere x e
where Kd is a coefficient of light attenuation. It is a complex process that involves many factors
which can not be addressed in full in a simple box model as the one used in this work. Therefore,
there is only one value of the downwelling irradiance used for calculation of light influence of algal
growth in this model. It is an average value calculated for the entire water column:
PAR
measurements in 1999 (RENK et al. 2001)
Iopt mean monthly values from measurements (RENK et at. 2001)
MODEL
0 30 60 90 120 150 180 210 240 270 300 330 360
days
Fig. 2.3 Iopt values in the model versus measurements in the Vistula Lagoon, after RENK et al. (2001).
water
= PAR
atmosphere
-Kd×
depth
1-
e
× ( )
Kd × depth
Coefficient for light attenuation is described as a sum of attenuation due to attenuation due to water
with dissolved substances and all types of material suspended in the water column described by the
model:
Kd = ext_water dissolved subst. + ext_phytopl. x PHYTOPLANKTON + ext_Ndet x Ndet
The light extinction of the dissolved substances was measured in water filtered through the 0.7 µm
GF/F Watmans Filter sampled in the Kleines Haff in August 2000. The average value for the
samples equaled to 0.51 (SIEGEL AND GERTH personal comm.). Water light attenuation coefficient
was chosen after KIRK (1994), equaled to 0.08.
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