Jędrasik J., Kowalewski M., Ołdakowski B., University of Gdansk, Institute of Oceanography Impact of the Vistula River waters on the Gulf of Gdańsk during European Commission project EUROCAT : European Catchments Changes and their Impact on the Coast Case Study VISCAT: The Vistula River Catchment and the Baltic Sea Coastal Zone

Plan: 1. The ecohydrodynamic model of the Baltic Sea General discription ProDeMo model – algorithm + modifications –Calibration, verification, validation – quality evaluation of the model – chosen results 2. Impact of the Vistula River on the Gulf of Gdańsk - examples 3. Conclusions

The ecohydrodynamic model of the Baltic Sea

ProDeMo model Atmosphere Water Sediment NUTRIENTS N-NO 3 P-PO 4 Si-SiO 4 N-NH 4 PHYTOPLANKTON Blue-green algae Spring diatoms Autumn diatoms Dinoflagellate Green algae DETRITUS C DETR P DETR Si DETR N DETR DISSOLVED OXYGEN N SED P SED Si SED Active layer Inactive layer ZOOPLANKTON Zooplankton C:N:P nutrient uptake 2 grazing 3 phytoplank. resp. 4 phytoplank. decay 5 sedimentation 6 nutr. release f. sed 7atmospheric dep. 8 denitrification 9 mineralization 10 zooplankt. resp. 11 sed.of P ads. on particles, 12 detritus sed. 13 zooplankt. decay 14 nitrogen fixation 15 nutrient deposition processes influen. dissolved oxygen 16 reaeration, 17 flux to atmo. due to over saturation 18 zooplankt. resp. 19 phytoplank. resp. 20 assimilation 21 mineralization 22 nitrification 23 denitrification

Calibration Verification Validation based at stations P1, P110, ZN2 for period as asessment of behavior of the model test how the model results fit the observation data

Monitoring stations at the southern Baltic The hydrodynamic model is based on the POM (Princeton Ocean Model). The numerical application of the model has been embedded on two nested grids: 1 NM for the Gulf of Gdańsk in 5 NM for the Baltic Sea. A “sigma” transformation for 18 layers are used.

Validation of the model – station P1 z = 0m

Validation of the model – station P1

Observed and modelled vertical distribution of the variable states during winter and summer seasons in 2001

The vertical distributions of the modelled parameters follows the observations, however better agreements have been achieved in the upper layer than in the layer below the halocline (60-70 m).

Quality of the ProDeMo model An excellent agreement for salinity, dissolved oxygen and temperature. Other compared parameters lie in the good range except nitrate nitrogen as acceptable and ammonium nitrogen low satisfactory.

Mean concentrations of the modelled parameters for 15 th June 1999

Variation in biomass and structure of phytoplankton modelled for 15 th June 1999

Distribution of phytoplankton at Gdansk Deep station P1 in period The vegetation seasons start with the high blooms of diatoms during the spring. During the summer dinoflagellates and green algae dominates. The blue-green algae are able to assimilate the nitrogen from the atmosphere. Their appearance varies from year to year since they prefer higher water temperature and solar radiation. Autumn diatoms starts to grow in September and they dominate trough whole autumn.

Annual input of the Vistula River into the Gulf of Gdańsk Annual input of the Vistula and other rivers into the Gulf of Gdańsk Vistula the second largest river of the Baltic Sea introduces into the Gulf of Gdańsk 85% of discharged fresh waters 90% of nitrogen compounds (it takes part 15% of N in the Baltic) 23% is retained at the Gulf 92% of phosphorus compounds (it takes part 20% of P in the Baltic) 34% is retained at the Gulf

Distributions of N-NO 3 and P-PO 4 in crossection through the Gulf of Gdańsk from mouth of the Vistula River to the station P1 at 4 th March 1995

Spreading of the Vistula waters at the Gulf of Gdansk during 11 April – 10 May 2000 The hydrodynamics influences on the nutrient and phytoplankton distributions. During the spring season influence of the Vistula River waters on the nutrient concentrations are even at the open waters of the Gulf of Gdańsk. 11 April – 10 May 2000, the main pathway of the Vistula River water - the North-West direction.

Sequence of surface distribution of phytoplankton biomass, nitrates and phosphates at the Gulf of Gdansk between February 22 – March

Conclusions Impact of the Vistula River on the Gulf of Gdańsk From among various effects of the Vistula River discharge on the environmental state of the coastal waters are: pathways of the Vistula River waters in the Gulf temporal and spatial dynamics of nutrients blooms and seasonal variations of phytoplankton biomass ProDeMo model calibrated, verified and validated using monitoring data for 9 years period , resulted in the model obtained evidences (high statistical evaluation) which permit to consider it as reliable tool for studding the coastal processes in the Gulf of Gdańsk. The model has properly described the seasonal distribution of nutrients, temperature and dissolved oxygen, however near the bottom it was overestimated. Other compared parameters lie in the good range of quality of model except nitrate nitrogen as acceptable and ammonium nitrogen low satisfactory. The biomass distributions of the five phytoplankton groups as well as time and places of their blooms appeared reliable.