Результаты разработки полуэмпирической теории фракционирования концентраций минерального фосфора и азота фитопланктоном в воде фотического слоя по данным мониторинга Севастопольской бухты

Abstract

The article focuses on the development of the theoretical basis of Academician V. Vernadsky concept of the unity of the processes of reproduction of living matter and its habitat conditions, taking into account the patterns of conditioning the marine environment resulting from primary production processes. The objectives of the survey were as follows: to study the distribution of mineral compounds of nitrogen (NO₂, NO₃, and NH₄) and phosphorus (PO₄) in the coastal waters of Sevastopol Bay based on the results of monitoring caried out in 2012–2014; to develop a semi-empirical mathematical model of the dynamic characteristics of phytoplankton mineral metabolism as a theoretical basis for assessing the effect of meteorological, thermohaline, and primary production processes on the biotic conditioning of marine environment; by comparing the results of observations and numerical experiments on the model, to obtain evidence of the existence of a natural biogeochemical mechanism for regulating the ratio of biogenic elements in water; and to determine the bifurcation role of switching limiting factors in the photic layer water and their effect on new primary phytoplankton production and energy dissipation. The work was carried out in the area with coordinates 44°36.930′N, 33°30.177′E. The hydrochemical parameters of the samples were determined in a certified laboratory. Primary production was analyzed by radiocarbon dating, with water temperature and duration of daytime taken into account. Nutrient consumption for organic matter formation was estimated involving the Zilov equation, while stoichiometric ratios and the degree of chemical limitation of production processes were calculated by the Redfield equation. A balance model of phytoplankton mineral metabolism was constructed involving the Burmaster–Chisholm, Monod, Michaelis–Menten, Dugdale, and Droop relations, and also the kinetic patterns of radioactive phosphorus (³²P) metabolism by unicellular algae. On the annual time scale, phytoplankton primary production was found to depend on the water temperature and duration of daytime, with phosphorus limitation prevailing. From the second half of the growing seasons, there was a tendency for the ratio of concentrations of mineral forms of nitrogen and phosphorus to reach a stationary stoichiometric value of the Redfield parameter (R_at = 16). The dependence of the shifts in limitation of production processes on the concentration of biogenic elements in the water was reliably described by power functions. The differential semi-empirical model had sufficient objective complexity to be used as a theoretical basis for describing the patterns of biogenic element fractionation by phytoplankton. In numerical experiments on the model, the rule of natural regulation of the productive characteristics for phytoplankton communities was confirmed: “Whenever the concentration of biogenic elements in the aquatic environment deviates from the standard or regionally specific stoichiometric ratio, the functioning of natural photosynthetic systems is always directed towards their restoration.” It was established that the primary production of phytoplankton affected the ratio of biogenic elements in the water due to its concentrating function for mineral forms of nitrogen and phosphorus. It was shown that at the system level, the effect of the phytoplankton production system manifests itself in the form of negative feedback according to the Le Chatelier–Brown principle; within certain limits, it boosts the biosynthesis of organic carbon due to lower specific costs of mineral phosphorus compared to nitrogen, and also due to accelerating the dissipation of energy flows as a result of the flow of additional energy into the biosphere.

Keywords: biogenic elements, phytoplankton primary production, stoichiometric ratios, theory of mineral metabolism, patterns of biotic conditioning of the marine environment, Sevastopol Bay, Black Sea