Natural-climatic and anthropogenic factors determining the self-purification capacity of shallow-water marine ecosystems in relation to reduced nitrogen forms

The paper considers natural-climatic and anthropogenic factors that determine differences in the self-purification capacity of the Sevastopol Bay ecosystems (its western, central, eastern parts and the Yuzhnaya Bay) in relation to the reduced nitrogen forms (ammonium and nitrites) by calculating the assimilation capacity. The authors took into account the intensity of the input sources of the studied forms of nitrogen, the rate of excretion from the ecosystem, the dynamic situation in the studied water areas and in the entire bay as well as the location of recreational facilities. For the first time, the factors were assessed that provide additional input of reduced forms of nitrogen associated with hypoxia during summer water stratification in local deepened areas in the upper bottom sediment layer, taking into account their particle size distribution. Further, the authors considered accumulation of organic matter and its destruction due to oxidized nitrogen forms and formation of reduced forms thereof. The currents in the central and southern parts of the Sevastopol Bay were calculated using a hydrodynamic model. The calculation results correspond to the current system in the mentioned water areas of the bay according to in situ data at different wind situations in the region. According to the calculations, it is possible that under certain hydrometeorological situations additional amount of ammonium and nitrites would flow from the Yuzhnaya Bay into the central part of the Sevastopol Bay.

Organic Matter of Bottom Sediments of the Crimean and Caucasian Coasts (Azov and Black Seas)

As part of the 113th cruise of the R/V “Professor Vodyanitsky”, research was conducted on organic pollution of bottom sediments in the coastal areas of Crimea and the Caucasus, as well as the water area in front of the Kerch Strait. Concentration of chloroformextractable substances was determined by the weight method and that of petroleum hydrocarbons was determined using infrared spectrometry. Both in 2020 and 2016 (the 83d cruise of the R/V “Professor Vodyanitsky”), properties of the bottom sediments of the Crimean and Caucasian coasts were typical of the marine soils of this region. This indicates that the studied water areas are generally in good condition. In accordance with the regional classification of bottom sediment pollution, the maximum concentrations of chloroform-extractable substances obtained for both the Black Sea and the Sea of Azov coast indicate pollution level III (23% of analysed samples). These values were found in bottom sediments in the Sevastopol water area (225 mg·100 g-1), in the coastal area of Cape Tarkhankut (120 mg·100 g-1) and Karadag (120 mg·100 g-1), the southern part of the Sea of Azov (125 mg·100 g-1) and Tuapse (110 mg·100 g-1). The content of chloroform-extractable substances in bottom sediments off the Black Sea coast of the Caucasus and the Sea of Azov coast is slightly lower than that off the Crimean coast. Pollution level II is assigned to bottom sediments in 46 % of the samples, with an average concentration of 72 mg·100 g-1 of air-dry solids. The rest (31 %) of the studied area was classified as conditionally clean (pollution level I, i. e. less than 50 mg·100 g-1). There has been a slight increase in the concentration of petroleum hydrocarbons in the bottom sediments of both the Black Sea and the Sea of Azov and their share in the total amount of chloroformextractable substances. In general, the level of pollution of bottom sediments by organic matter remained unchanged if compared with previous years, in particular with the data from 2016

Hydrophysical research in the Kruglaya Bay (Sevastopol)

On the basis of two hydrophysical surveys (August 28 and November 14, 2019), the spatial distribution was investigated of temperature, salinity, total suspended matter, dissolved organic matter features, and total suspended matter dynamic activity in the waters of the Kruglaya Bay. The horizontal and vertical distributions of these characteristics were considered. The hydrophysical parameters were measured from a small vessel at anchored stations using Kondor Sounding Complex. The analysis of obtained distributions showed that less saline and more turbid waters were observed in the apex of the bay. The highest content of suspended particles and dissolved organic matter were detected in this water area. An almost uniform stratification of hydrological parameters and total suspended matter concentration were observed in the vertical distribution over the entire water area of the bay. In the vertical dissolved organic matter distribution, an increase under the water surface layer of ~ 1–5 m was observed both in August and in November. This layer was more pronounced in November. The total suspended matter content in the surface water layer in August 2019 was on average twice as high as in November of the same year, and the dissolved organic matter concentration was lower.

Comprehensive Study of Wave and Lithodynamic Processes in the Coastal Area of the Village of Morskoye (Eastern Crimea)

Wind waves can have a significant impact on the coastal infrastructure. The paper aims at a comprehensive study of regional characteristics of wind waves near the village of Morskoye (south-eastern coast of Crimea), which are necessary to develop a project of reconstruction of the highway adjacent to the coastal area. Space images and cartographic information were used to study the beach dynamics in the studied area. It is shown that before construction of the coast protection structures the beach width in the studied area was 25–30 m, whereas after the construction it narrowed down to 15–25 m. Based on the wind wave reanalysis data obtained using SWAN spectral model and ERA-Interim surface wind fields for 1979–2017, regime characteristics of waves in the coastal zone of Morskoye were calculated. It was found that waves with average periods of 3.0–3.5 s have the maximum recurrence (over 16 %). Wind waves coming from SE-SSE sector have the highest recurrence rate. Estimates were obtained for the extreme characteristics of wind waves that may occur once in a given number of years. The SWASH hydrodynamic model was used to perform mathematical modelling of wave run-up on the coastal area. In their calculations the authors used a regular grid of the coastal relief with high spatial resolution based on the interpolation of topo-geodetic and bathymetric survey results. An incoming wave was given as a soliton of 2.0; 3.0 and 3.4 m high. It was found that with the incoming wave height of 2.0 m, the vertical wave splash in the studied area varies within 1.7–2.2 m. At a height of 3.4 m, the splash reaches 1.8–2.9 m. In this case the beach is flooded completely. During the run-up, wave current velocity amounts up to 5 m/s. Along the lower boundary of the cliff the bottom maximum current velocity reaches 1.5–1.75 m/s. At such velocities near the cliff, the beach consisting of material with the grain size up to 60–90 mm can be eroded.