Formation of the Ecological Risk Zones in the Coastal Water Areas of the Kerch Strait

K. I. Gurov✉, Yu. S. Gurova, N. A. Orekhova, S. K. Konovalov

Marine Hydrophysical Institute of RAS, Sevastopol, Russian Federation

✉ e-mail: gurovki@gmail.com

Abstract

Purpose. The paper is aimed at studying the features of hydrological and hydrochemical structure of the bottom water layer and the distribution of geochemical parameters in the bottom sediments, and also at evaluating the basic factors in formation of the redox conditions in the bottom sediments of the Kerch Strait.

Methods and Results. The Kerch Strait ecosystem was comprehensively investigated in July and September, 2020. Hydrochemical studies of the water column were carried out using the standard hydrochemical methods. The profiles of the vertical distribution of oxygen, hydrogen sulfide, oxidized and reduced forms of iron in the pore waters were obtained, and also the geochemical characteristics of bottom sediments were defined. The features of their spatial and vertical distribution were considered. The sediment columns were sampled by a hand sampler and an acrylic soil tube (its internal diameter is 60 mm) with a vacuum seal. The pore water chemical profile was obtained by the polarographic method of analysis that included a glass Au-Hg-microelectrode. Hydrochemical structure of the surface horizon waters in July was noted to be conditioned by the Black Sea water contribution, and that of the bottom horizon waters – by the Azov Sea waters. It has been established that in a summer period in the Taman Gulf surface layer, an increased content of biogenic substances took place; and the increased water temperature and salinity, as well as active oxygen consumption in the bottom water layer decreased the degree of its saturation in the central part of the gulf. As a result, this favored the Taman Gulf silting, intensive oxygen consumption for oxidizing organic matter and the development of anaerobic conditions, and the hydrogen sulfide arising already in the surface layer of bottom sediments. In September, the main contribution was made by the Black Sea waters, that promoted the bottom water saturation with oxygen and the nutrient concentration decrease by 2–3 times. At that in September, oxygen penetrated into the sediment up to 2 mm, and the hydrogen sulfide content was 3 times lower than that in July.

Conclusions. It has been revealed that the hampered water exchange in the Taman Gulf region and the accumulation of organic matter in the bottom sediments due to the inflow of a significant amount of suspended matter, resulted in a limitation of the oxygen flow to the water bottom layer, whereas the fine-dispersion character of the sediments hampered penetration of oxygen into the bottom sediments. As a result, this contributed to the Taman Gulf silting, intensive oxygen consumption for oxidizing the organic matter and the development of anaerobic conditions, and to arising of hydrogen sulfide already in the surface layer of bottom sediments. The recorded at present anoxic conditions in the sediments upper layer can result in development of the oxygen deficiency in the bottom water layer and in formation of the ecological risk zones in the ecosystem of the Kerch Strait.

Keywords

hydrological parameters, hydrochemical parameters, currents, bottom sediments, pore waters, oxygen, voltammetry, granulometric composition, organic carbon, Kerch Strait

Acknowledgements

The investigation was carried out within the framework of the state assignment of the MHI RAS on themes FNNN-2021-0005 “Complex interdisciplinary studies of oceanologic processes which determine functioning and evolution of ecosystems in the coastal zones of the Black Sea and the Sea of Azov” and FNNN-2022-0003 «Assessment of the dependence of CO2 fluxes on the surface of the Black Sea on the physico-chemical characteristics of the marine environment and obtaining characteristics of seasonal changes in fluxes», and with the support of the RFBR project No. 20-35-90103.

Original russian text

Original Russian Text © The Authors, 2022, published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 38, Iss. 6, pp. 637-654 (2022)

For citation

Gurov, K.I., Gurova, Yu.S., Orekhova, N.A. and Konovalov, S.K., 2022. Formation of the Ecological Risk Zones in the Coastal Water Areas of the Kerch Strait. Physical Oceanography, 29(6), pp. 619-635. doi:10.22449/1573-160X-2022-6-619-635

DOI

10.22449/1573-160X-2022-6-619-635

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