Studying the Dynamics of the Transformation Processes for Nitrogen and Phosphorus Compounds in the Ecosystem of the Vistula Lagoon of the Baltic Sea Using Mathematical Modeling

A systematic study of the interaction of hydrobiological, hydrochemical, hydrological, and hydrophysical processes that occur in the ecosystem of the Vistula Lagoon (VL) of the Baltic Sea has been carried out using mathematical modeling and taking into account the processes in the active layer of bottom sediments (BSs). The features of the dynamics of nitrogen and phosphorus compounds, the turnover time, and the components of the balance of compounds of biogenic elements in the VL ecosystem, as well as the degree of their temporal variability, have been analyzed. It is shown that the variability of nitrogen and phosphorus compounds in the aquatic environment increases in spring and autumn periods. This is due to an increase in river flow into the lagoon and an increase in the level of external biogenic load on the water area of the VL. Model calculations of matter fluxes allow us to state that the inputs of dissolved organic and suspended matter into the lagoon from external sources and the removal to the Baltic Sea are important processes that significantly affect their content in the VL ecosystem. It has been established that under strong winds the process of sedimentation of suspensions can be largely blocked, and the intensity of BS resuspension can increase significantly. An analysis of the main qualitative and quantitative features of the nature of the temporal dynamics of the DON and DOP turnover times, as well as the mineral compounds of nitrogen and phosphorus, indicates a close conjugation of the processes of transformation of dissolved organic and inorganic substances in the water of the VL. A quantitative assessment of the processes of consumption and excretion of compounds of biogenic elements by different groups of aquatic organisms has been performed, and the important role of heterotrophic bacterioplankton and protozoa in the processes of transformation of compounds of nutrients in the VL ecosystem has been shown. The model can be used for scenario modeling and analyzing possible changes in the VL ecosystem under changing climatic and anthropogenic conditions.