Seasonal Dynamics of Microbial Processes in Bottom Sediments of the Sevastopol Coastal Area

Abstract

A seasonal study of microbial methane oxidation (MO) and sulfate reduction (SR) processes in bottom sediments was carried out at five stations in the estuarian Sevastopol coastal area, which differed in their sedimentation and geochemical conditions. High methane concentrations in bottom sediments, as well as accordingly high MO rates, were obtained at stations marked by high organic carbon (C_org) concentrations. The dependence of these values was found to be exponential, whereas for SR, the amount of organic carbon was not the limiting factor. For the studied stations, the integral SR rates ranged from 2.9 to 11.3 mmol m^–2 day^–1. The trends of the SR rate have opposite directions for the open and closed parts of the sea: SR decreased during study period at the center of the bay, while in the open sea area it increased. The MO rates varied in a wide range from 0.0001 to 3.6 mmol m^–2 day^–1; the highest were obtained in C_org-rich sediments of the central part of the bay. Only at one station, where the mean annual C_org content in sediments reached 3.39%, did the methane concentration in sediment pore water exceed the calculated solubility.