Methane and hydrogen sulfide in bottom sediments at the sites of dredging and underwater storage of soils in the Sea of Azov

The results of expedition studies aimed at studying the distribution of concentrations of methane and hydrogen sulfide in bottom sediments at the sites of dredging and underwater storage of soils in the Taganrog Bay of the Sea of Azov are considered. It is shown that the deposits to be developed in the seaport of Taganrog, Taganrog approach and Azov-Don sea channels are characterized by high concentrations of methane (1.9–47.4$\mu$g/g) and hydrogen sulfide (0.194–2.24mg/g), by an order of magnitude or more exceeding their values in nearby areas located outside navigable channels and underwater dumps of soil. The percentage of methane from the sum of the studied reduced gases (methanization coefficient) in the bottom sediments, depending on the sampling station, varies in the range of 0.014–15.08%, with the maximum values of the methanization coefficient in the sediments of the Taganrog approach channel. The minimum values of the methanization coefficient are observed in the sediments of the “background” sites, which indicates a significant dominance of the process of sulfate reduction over the process of methanogenesis during the decomposition of organic substances in the upper horizons of bottom sediments unaffected by dredging. There was no clear relationship between the concentrations of methane and hydrogen sulfide in the sediments of navigable channels and underwater dumps of soil, which, along with relatively high values of the methanization coefficient, may indicate in general the absence of an inhibitory effect of the sulfate reduction process on the formation of methane.