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The Odra Fiood Event In A Coupled Physicai-Chemical-Bioiogicai Model
Thomas Neumann
Institut fur Ostseeforsehung
Seestrafie 15
18! 19 Rostock-Waroemiinde
Abstract
The Odra flood event of the summer 1997 was simulated with a coupled physical-chemicaibiologicai
model. The circulation model is a baroclinie model with free surface, a horizontal
resolution of one nautical mile and a vertical resolution of two meters. Four state variables
dissolved nitrogen, phytoplankton, zooplankton and detritus form a nitrogen cycle and are coupled
to the circulation model by means of the advection-diffusion equation. Meteorological forcing was
obtained from the permanent buoy station in the Pomeranian Bight of the Institute of Baltic Sea
Research. Odra runoff into the Odra Haff was derived from a barotropic model taken water level
differences into account.
Model results show an enhanced chlorophyll a concentration of about 20 mg/m’ in the Pomeranian
Bight. Influenced by easterly winds in August the high chlorophyll a concentration was located in
the west part of the Pomeranian Bight. No remarkable amounts of these water masses have left the
Pomeranian Bight. Around the 27th August the chlorophyll a plume reaches up to the north tip of
Ruegen island. Most of the additional nitrogen was sedimentated near the Swina mouth and
offshore of the Usedom coast. The calm weather in August in conjunction with the less saline water
from the Swina mouth formed a well pronounced pycnocline with a depth of about 8 meters. Under
these conditions, high sedimentation rate and strong stratification, anoxic conditions as regional
limited impact could be expected.
After strong winds in the beginning of September the water in the Pomeranian Bight was mixed up
and concentrations of dissolved and particulate nitrogen have recovered to normal values.
