Simulation of Seasonal Hydrodynamic Regime in the Sevastopol Bay and of Assessment of the Self-Purification Capacity of its Ecosystem

The numerical experiments were carried out to assess the hydrodynamic regime of the eastern part of the Sevastopol Bay, subject to the Chernaya River runoff (high- and low-water periods) and the Yuzhnaya Bay, subject to the technogenic load using the hydrothermodynamic block of the numerical three-dimensional unsteady model MECCA (Model for Estuarine and Coastal Circulation Assessment).The simulated hydrodynamic parameters of the selected parts of the Sevastopol Bay were used to analyze the self-purification capacity of their water bodies by calculating the assimilation capacity for inorganic phosphorus. Phosphates suggested as a priority pollutant in municipal and storm runoffs in the water area of the bay and a determining factor of its in the bay eutrophication. At the same time, to neutralize the differences in the water volumes of the studied water areas when calculating the self-purification ability, estimates of the specific assimilation capacity of their ecosystems were obtained.According to the simulations for the eastern apex part of the bay during high-water period, the water circulation in the surface layer contributes to the spread of pollutants throughout the entire water area of the bay. During the low-water period in the eastern part of the bay, currents prevail, directed towards the Chernaya River mouth in the surface and in the bottom water layer both in the northwestern and western wind directions. It contributes to pollutant accumulation in this part of the bay, thus reducing ability to self-purification.Possible reasons for the low self-purification capacity of the ecosystem of the eastern part of the Sevastopol Bay with respect to inorganic phosphorus are analyzed, which are associated both with the volumes of incoming Chernaya River waters during winter high- and summer low-water periods, as well as with the features of the morphometric structure of the water area bottom.For the Yuzhnaya Bay water area, the hydrodynamic regime is defined by a difficult water exchange with the main water area. Ventilation of the waters of the Yuzhnaya Bay is mainly determined by the wind regime, as a result of which the waters are either trapped in the bay or carried out of it, which undoubtedly affects the self-purification capacity of its ecosystem.