Limitation of Phytoplankton Primary Production by Biogenic Elements in the Coastal Waters of the Azov-Black Sea Basin as a Natural Factor in Conditioning the Marine Environment

The study focuses on determining the concentrations of nitrites, nitrates, ammonium, and mineral phosphorus in the waters of the Azov-Black Sea basin. It investigates the limitation of primary phytoplankton production in the region, and evaluates the impact of bifurcation (switching of limiting factors) on the natural conditioning of the marine environment concerning biogenic elements. The research was conducted during 2023–2024 in Streletskaya Bay (Sevastopol), coastal areas of the northeastern Black Sea, and the Sea of Azov. The limiting function was assessed using the Redfield equation. The key findings indicate that the dependencies of the Redfield parameter on phosphate (PO4) concentration and total nitrogen compounds are described by power functions. A rule for natural regulation of phytoplankton communities was established: whenever the concentration of biogenic elements in the aquatic environment deviates from the region-specific stoichiometric ratio, the functioning of photosynthetic systems always acts to restore it. The validity of this rule was confirmed using a mathematical model and was supported by annual observational data on biogenic element concentrations in Streletskaya Bay.