1. Тихонова Е. А. (Tikhonova E. A.)
2. Соловьева О. В. (Soloveva О. V.)
3. Gurov К. I.
   
   Marine Hydrophysical Institute of RAS, Sevastopol, Russian Federation (ru)

Purpose. The purpose of the study is to identify the features of spatial and vertical distribution of hydrocarbons in the bottom sediments and to assess the likely sources of their ingoing to the port coastal water area (at the example of the Streletskaya Bay).

Methods and Results. The samples of the bottom sediments surface layer (5 sampling stations) and the columns of marine sediments (2 columns) were taken during the joint expedition of the Department of Marine Sanitary Hydrobiology (FRC IBSS) and the Department of Marine Biogeochemistry (FRC MHI) in July 2021 as a part of a long-term monitoring of the Sevastopol bays. The features of spatial distribution in the sediment surface layer (0–5 cm), the profiles of vertical distribution of the geochemical characteristics of bottom sediments, hydrocarbons and n-alkanes, and the individual diagnostic indices (markers) were analyzed. The history of hydrocarbon accumulation resulted from the 50-year long human activity was considered, and the anthropogenic load on the bay water area was assessed.

Conclusions. The bottom sediments composition of the Streletskaya Bay promotes the accumulation of hydrocarbons: the aleurite-pelitic silts of high natural humidity are ubiquitous, and the organic carbon average contents in the surface layer (5.1%) and in the bottom sediments thickness (5.3%) significantly exceed the values typical of the other water areas in the Sevastopol region (1.2–3.7%). The hydrocarbon concentrations in bottom sediments ranged from 328 to 2175 mg/kg (the average value is 1160 mg/kg), that exceeds the pollution levels in many port areas of the Black Sea. The concentrations of the studied substances increase from the top of the bay to its apex. The composition of n-alkanes and the nature of chromatograms indicate a mixed origin of hydrocarbons at the dominating allochthonous (incoming from land) compounds, and also the presence of n-alkanes of the autochthonous and petroleum origin. Based on the data resulted from the chronology of hydrocarbon accumulation, the maximum anthropogenic loads on the bay fell on the periods 1967–1973 and 1985–1991. These were the years of intensive economic development of the city and the population growth in the sub-district adjacent to the studied water area in the Streletskaya Bay. In recent years, the intensity of hydrocarbon accumulation has been decreasing, but the signs of oil pollution are still present.