Levels and Sources of Hydrocarbons in Water and Sediments of the Northern Caspian

Inna A. Nemirovskaya, P. O. Zavialov, А. В. Медведева, Boris V. Konovalov, A. K. Kurbaniyazov, Ivan B. Zavialov

2026

Data confidence 70 medium

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Abstract

Abstract Hydrocarbons (aliphatic hydrocarbons—AHCs and polycyclic aromatic hydrocarbons—PAHs) were studied in water and bottom sediments at three sites in the Northern Caspian Sea (the western site in the Volga Delta, Bakhtemir arm; the northern site in the Atyrau district; and the southern site in the coastal zone of Aktau city). The highest concentrations (AHCs—up to 170 μg/L, PAHs—up to 2080 ng/L) were found in surface waters of the northern site. The presence of significant correlation between the distributions of suspended particulate matter, chlorophyll a, AHCs, and PAHs (r = 0.86–0.98) may indicate natural sources of the hydrocarbons. In bottom sediments, AHC concentrations (32–275 μg/g) exceeded background values and, according to the composition of alkanes in the high-molecular region, were petroleum-related (phytane dominated over pristane due to low CPI values). Individual PAH levels did not reach the permissible concentrations established by the Canadian Marine Sediment Quality Criteria. However, markers at some stations indicated petroleum- and pyrogenic-related origins of the polyarenes.