The Oder Estuary - IOW

ecalculated into salinity using formula calculated by MLODZINSKA (1980) for the Szczecin
Lagoon waters:
S‰ = 1,768 Cl ‰ + 0,072
Sea water inflows from the Pomeranian Bight were calculated on the basis of the following
relationship:
salinity
Szczecin−Lagoon
( waterflow
=
sea−water
* salinity
( waterflow
sea−water
sea−water
+ waterflow
+ waterflow
Assuming that the salinity of the riverine waters equals zero, we receive:
salinity
fresh−water
fresh−water
* salinity
)
sea−water
waterflowsea− water =
× waterflow fresh−water
( salinitysea−water
− salinitySzczecin−Lagoon
)
fresh−water
where mean monthly salinity is expressed in PSU and monthly water inflow in cub. km. The annual
amount of saline water (waterflowsea-water) entering the Lagoon calculated with that method
amounted to 3.6 km 3 a -1 on average, ranging from 5.2 to 1.6 km 3 a -1 .
Nutrient concentrations of the sea water entering the Szczecin Lagoon were calculated on the basis
of data from the Baltic Environmental Data Base (Stockholm University), available from
http://www.bed.su.se (BED 2002). Mean values, with monthly resolution, calculated from the area
of the inner part of the Pomeranian Bight (53 o 54 - 54 o 10’ N and 13 o 47’ - 15 o 32’ E) for the period
1993-98 were used. The average annual value of Ntot amounted to 34.8 mmol m -3 and Ptot
amounted to 1.22 mmol m -3 .
2.3 Parameterization of the biogeochemical processes
2.3.1 Phytoplankton growth (nutrient uptake)
The phytoplankton composition in the Lagoon changes throughout the vegetation season with
spring diatom dominance and summer dominance of blue-green algae. Model represents all
phytoplankton species as one group of phytoplankton and thus one state variable. Seasonal changes
of phytoplankton composition are represented in the model through changing values of some
parameters, such as light optimum and assimilation number, that mimic changing requirements of
different species, or mortality ratio – representing increase of phytoplankton mortality due to
grazing is summer months.
The phytoplankton growth (= nutrient uptake) is equivalent to the net primary production in the
model. Phytoplankton growth depends from temperature and can be limited by light and nutrient
availability according to von Liebig’s law of the minimum. Since phytoplankton as a state variable
is represented in the model in nitrogen units, phosphorus uptake is recalculated into nitrogen with a
fixed Redfield ratio.
growth (uptakeN)= µmax x f(Temp) x [MIN (f(PAR), f(DIN), f(PO4))] x PHYTOPLANKTON
2.3.2 Temperature dependence of growth
First part of the equation:
µmax x f(Temp),
105
)