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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-chemicai- 
biologicai 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.