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The influence of the Hel upwelling (Baltic Sea) on nutrient concentrations and primary production - the results of an ecohydrodynamic model

Kowalewski M.

Oceanologia

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2005

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No. 47 (4)

567-590

EN

An ecohydrodynamic model was used to investigate the effect of the Hel upwelling on nutrient concentrations, primary production and phytoplankton biomass. The model covered the whole Baltic Sea with a 5 NM grid spacing and the Gulf of Gdańsk with a 1 NM grid spacing. Validation indicated good agreement between model results and measurements in the Gdańsk Deep, and slightly weaker concord for the Hel upwelling area. The vertical nutrient fluxes associated with up- and downwelling in the Hel region were simulated for two 30-day periods in 2000. The nutrient input resulting from long-term upwelling is comparable to the load carried into the Gulf of Gdańsk by the Vistula (Wisła), the largest river in the vicinity. Performed at times when upwelling was almost permanent, the simulations showed elevated nutrient concentrations in surface waters. This was especially distinct in spring when primary production and phytoplankton biomass were both higher. In late summer, however, upwelling caused primary production to decrease, despite the elevated nutrient levels.

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Ecohydrodynamic model of the Baltic Sea. Part 2. Validation of the model

Jędrasik J., Szymelfenig M.

Oceanologia

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2005

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No. 47 (4)

543-566

EN

The ecohydrodynamic model for the Baltic Sea consists of two interacting parts: one describes the hydrodynamics of the water (3HD), the other organic matter production and destruction (ProDeMo). The results of the simulation were validated. The modelled processes were compared with direct observations, which demonstrated the recurrence of cycles, from the spring diatom blooms through the summer depletion of nutrient salts and algal blooms, to autumn blooms of diatoms and the subsequent destruction of organic matter, and intensified mineralisation of detritus in winter. Calibration yielded a set of coefficients complementing the algorithm of equations describing the production and destruction of organic matter in the coastal zone. Verification of the model has demonstrated that in multi-year simulations it is stable and also that it follows the laws of conservation of mass and energy. The third procedural stage of the model investigation was validation, in which statistical measures in the form of bias, correlation coefficients and effectiveness between simulations and observations not used in calibration describe the quality of ecohydrodynamic modelling in southern Baltic Sea waters.

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Ecohydrodynamic model of the Baltic Sea. Part 1. Description of the ProDeMo model

Ołdakowski B., Kowalewski M., Jędrasik J., Szymelfenig M.

Oceanologia

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2005

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No. 47 (4)

477-516

EN

The ProDeMo (Production and Destruction of Organic Matter Model), a 3D coupled hydrodynamic-ecological model, was formulated and applied to the whole Baltic Sea and the subregion of the Gulf of Gdansk. It describes nutrient cycles (phosphorus, nitrogen, silicon) through the food web with 15 state variables, oxygen conditions and the parameterisation of water-sediment interactions. The present version of the model takes two groups of phytoplankton - diatoms and non-diatoms - as well as zooplankton into consideration. It covers the flow of matter and energy in the sea, including river discharges and atmospheric deposition. Numerical applications are embedded on a 1 NM grid for the Gulf of Gdansk and a 5 NM grid for the Baltic Sea. Since the model results largely concur with observations, the model can be regarded as a reliable tool for analysing the behaviour of the Baltic ecosystem. Some examples of the spatial-temporal variability of the most important biological and chemical parameters are presented. The model results are compared with those of other modelling research in the Baltic Sea. Both the ProDeMo model algorithm and its computing procedures need to be further developed. The next version should therefore enable more phytoplankton groups to be defined, for example cyanobacteria, which are able to take up molecular nitrogen from the atmosphere (nitrogen fixation). Additionally, the sediment phase should be divided into active and non-active layers.