A. V. Leonov

Mathematical Modeling of Organogenic Material Biotransformation Processes for Studying the Conditions of Water Eutrophication in the Caspian Sea Surface Layer

A mathematical model based on average long-term data on water temperature, illumination, transparency, and nutrient content is used to calculate annual variations in the concentrations of organic and inorganic fractions of nutrients (C, N, Si, and P) in ten water areas in the Caspian Sea. The eutrophication of sea environment is examined with special emphasis on the increase in the biomass of aquatic animals (in particular, phyto- and zooplankton), the rate and duration of periods of plankton blooming, and changes in the conditions of nutrient limiting of primary production processes in different parts of the sea. Relationships between the inorganic components of N and P in river runoff and sea water areas are established. The obtained Nmin/DIP ratios show P primary production to be limited in the zone of influence of the Volga runoff, P and N primary production to be limited in other northern parts of the sea, and N primary production to be mainly limited in the middle and southern parts of the sea.

Sulfate reduction in natural water bodies. 1. The effect of environmental factors and the measured rates of the process

Sulfate reduction is an important oxidation process involving transformation of organic matter and its components and taking place in the aquatic environment and bottom sediments of water bodies (both fresh and marine) under anaerobic conditions. The intensification of sulfate reduction in water bodies is a sign of a stronger anthropogenic impact on the environment and natural water bodies. The development of sulfate reduction under natural conditions reflects the influence of many environmental factors. The effect of the most important factors (the concentration of organic matter and its components and sulfates, the temperature of aquatic environment, and the abundance and activity of sulfate-reducing bacteria) on the process of sulfate reduction in the aquatic environment and bottom sediments in water bodies is considered.

Nutrient Input into the Caspian Sea with River Runoff

Long-term observational data are used to compare and analyze time and space variations in the concentrations of nutrients in the water of major rivers flowing into the Caspian Sea and assess the nutrients runoff into the sea. Annual variations in the normal monthly values of river runoff and nutrient compound concentrations and input into the sea are considered (18 compounds and considered for the Volga, Ural, Terek, Sulak, and Samur, and 7 compounds are considered for the Kura). The Volga contribution to nutrient input into the sea is found to vary from 77 to 94% with the average of 86%.

Restoration of mean monthly thermohaline fields in Tatar Strait

Statistical modeling and GIS “Sakhalin Shelf” are used to restore the annual variations of water temperature and salinity at standard oceanographic stations in Tatar Strait, where observation series are about 45 years long. Numerical modeling techniques with the help of Bergen University model are used to restore the spatial fields of water temperature and salinity. Analysis of calculation results made it possible to identify new features of the hydrological regime in the strait, in particular, during winter, for which no generalizations have been made before.

Transformations of biogenic substances in Tatar Strait water (the Sea of Japan): Analysis of mathematical modeling results

The state of the marine environment (the temperature, light intensity, transparency, biogenic load) in Tatar Strait was assessed based on mean annual data from literary sources and with the use of GIS “Sakhalin Shelf.” The entire strait was divided into three regions (northern, southwestern, and southeastern), and water exchange between them for each month was estimated by using Bergen Oceanic Model. The information about the state of the marine environment and water exchange characteristics was used as input data for a hydroecological model, which enabled the assessment of annual variations of biogenic substance concentrations and biomasses of microorganisms (heterotrophic bacteria, three groups of phytoplankton, and two groups of zooplankton) in the strait regions chosen. The development conditions of microorganism biomasses within the year can be characterized by their activity indices (specific growth rates), the values of internal fluxes of biogenic substances, and calculated bioproductivity values. The calculated biogenic substance concentrations and phytoplankton bioproductivity values showed good agreement with the estimates for the Sea of Japan and Tatar Strait available from the literature.

Mathematical modeling of the ecosystem functioning conditions in the Chupa Estuary of the White Sea: Transformation of organogenic substances and bioproductivity of the marine environment

The use of a mathematical model, describing the transformations of organic and mineral compounds of C, Si, N, and P for the generalization of hydrological, hydrochemical, and hydrobiological data on nine regions in the White Sea is demonstrated. The regions examined include the head of Kandalaksha Gulf, Dvina Gulf, Mezen Gulf, Onega Bay, the Solovetskie Islands’ area, the central, deep-water part (or Basin), Gorlo, Voronka, and the Chupa Estuary. The results of modeling the transformations of biogenic substances in the water areas of the Chupa Estuary, and other gulfs and bays in the White Sea are compared and analyzed. Calculated variations in the concentrations of biogenic substances and detritus, microorganism biomasses, characteristics of their activity (specific growth rates and biomass turnover times) within a year are presented and discussed. The estimated characteristics are shown to agree with observational data. Particular attention is paid to estimating the organic matter production rates by phytoplankton and calculating balances of biogenic compounds in the Chupa Estuary.

Studying the Ecosystem Functioning Conditions in Aniva Bay–La Perouse Strait

An atlas of oceanographic data on the shelf zone of Sakhalin Island and a mathematical model describing the transformations of nutrient compounds (N, P, Si, C) are used to study the biotransformation and transport of organic and mineral components of these elements in the La Perouse Strait. To make the analysis more convenient, the area under examination was divided into four zones, which differ in the conditions of transport of matter in water flows. Transport calculations are made using a complex graphic method with geostrophic approximation, which takes into account the results of instrumental observations of flow velocities, sea level variations, and annual variations in the water volumes. The obtained patterns of dynamics of nutrient compounds are compared with the results of modeling of internal and external fluxes of those components. Calculated fluxes of the elements were used to assess the rate of chemicals and biomass transport through the boundaries of water areas (in particular, between the Seas of Japan and Okhotsk).

Petroleum hydrocarbons in the waters of major tributaries of the White Sea and its water areas: A review of available information

The White Sea is a natural analogue of arctic seas. The pollution of the sea by petroleum hydrocarbons is not high now. However, the load on sea ecosystem can increase in the nearest future because of the anticipated industrial development in its watershed, including an increase in oil, coal, and diamond production. The specific features of the nature of arctic marine systems (hydrological, ice, hydrobiological, hydrochemical, and radiation regimes), and the poor knowledge of the conditions of dispersion, transformation, and utilization of petroleum hydrocarbons in such seas make their ecological studies especially important. Petroleum hydrocarbon concentrations in the waters of tributaries and water areas of the White Sea (for 1980–2006 and 1989–2006, respectively) were evaluated using literary and authors’ data. Analysis of the collected materials shows that the majority of petroleum hydrocarbons enter the sea’s water areas with river runoff. Petroleum hydrocarbon concentrations were evaluated in major tributaries of the sea, including the rivers of Northern Dvina, Onega, Mezen, Niva, Kem, and Keret, delivering petroleum hydrocarbons into the bays of Dvina, Onega, Mezen, and Kandalaksha, water area near the Solovetskie Islands, and Chupa Bay, respectively (Bay — Gulf). Model calculations should yield within-year variations in petroleum hydrocarbon concentrations in different part of the sea (under a correctly specified load) and the conditions of their biotransformation and horizontal transport through the boundaries between areas within the sea.

Modeling of the marine environmental pollution by petroleum hydrocarbons and their biotransformation in Tatar Strait waters

A hydroecological model is used for simultaneous studying water pollution processes by petroleum hydrocarbons and their decay under the oceanographic conditions of Tatar Strait. The model calculations were based on long-term averaged observational data on interannual variations of water temperature, light intensity, and transparency. Some oceanographic characteristics of the strait were reconstructed with the help of GIS “Sakhalin Shelf.” The strait’s water area was divided into three regions, and water exchange between them and the neighboring regions of the Sea of Japan was estimated by a hydrodynamic model. The results of the study made it possible to assess interannual variations in the concentrations and inner fluxes of petroleum hydrocarbons, oil-oxidizing bacteria biomasses, and the characteristics of their oxidation activity.

The Role of Microorganisms in the Transformation of Biogenic Substances in the Caspian Sea Ecosystem: An Assessment Based on Mathematical Modeling

A hydroecological model is used to study the transformations of biogenic-element (N, P, C, and Si) compounds in different parts of the Caspian Sea. The existing notions of the biotransformation processes of these compounds in the marine environment are formalized. The state of the marine environment is characterized based on calculated annual dynamics of biogenic element concentrations, their relationships, and internal fluxes. Relationships between the concentrations of N and P mineral components are used to establish distinctions between different parts of the sea in the conditions of primary production limited by biogenic elements, as well as the development conditions of aquatic lifeforms (nutrient consumption, release of metabolic products, and detritus formation).