Hydrocarbons composition of sea bottom sediments (Balaklava Bay, Black Sea)

Coastal regions are zones of active anthropogenic impact. The present environmental problems of Balaklava Bay (Black Sea), which has an increased anthropogenic load for a long time, are of growing interest. It is known that high concentrations of hydrocarbons (HCs) negatively affect the life processes of hydrobionts. The purpose of this work is to determine the content and spatial distribution of HCs as well as to assess the possible sources of their input in the bottom sediments of Balaklava Bay. The identification and quantitative determination of total HC content were carried out by a gas chromatography method on a gas chromatograph "Crystal 5000.2" equipped with a flame ionization detector and calibrated with a mixture of hydrocarbons (C-10-C-40). n-hexane was used as an extractant of HCs. It was found that the total amount of HCs in sediments varied from 21 to 2385 mg/kg, and n-alkane concentrations varied from 1 to 154 mg/kg. The HCs are distributed in bottom sediments mosaically with the maximum concentrations in the central part of the bay and the minimum contents in its open part. It was determined that identified n-alkanes of bottom sediments ranged from C-13 to C-35 and had a bimodal distribution, which indicates a mixed origin of hydrocarbons. The calculated markers indicate a predominantly terrigenous origin (TAR, Alkterr, n-ary sumation C25-35/ n-ary sumation C15-21(odd)) of HCs as well as chronic oil pollution (CPI2, UCM/R) of that area. Diagnostic indices used for the differentiation of petroleum from biogenic hydrocarbons allow us to assume the predominant presence of natural HCs.