Spatial and temporal distribution of hydrogen sulfide and sulfur species in coastal marine sediments collected from Osaka Bay, Japan

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The identification of sulfur species in coastal marine sediments provides insight into the sulfur cycle in coastal seas. This study revealed the spatial and temporal distribution of hydrogen sulfide in the sediment pore water and sulfur species in the marine sediments in Osaka Bay, Japan using a combination of detection tubes with the formation of a color band of lead sulfide and X-ray absorption fine structure spectroscopy to identify sulfur species. The sulfur species present in the sediment in this study were somewhat affected by the sediment pore water, and the solid sulfur species identified in the surface sediments were sulfate, thiosulfate, elemental sulfur, and pyrite. These results revealed that the process of change in the sulfur species in the sediments could be categorized into three subprocesses. (1) Hydrogen sulfide was generated in the sediment pore water and scavenged by oxidation into sulfur and pyrite formation. Pyrite was successively oxidized into thiosulfate and sulfate when the dissolved oxygen in the bottom water was sufficient. (2) When the dissolved oxygen was depleted at the innermost part of the Bay in October and November, pyrite might have been oxidized into sulfate by iron and manganese in the sediment. (3) For the western and southern parts of the Bay, because vertical mixing supplies oxygen to the seabed, the formation and oxidative scavenging of hydrogen sulfide in the sediment pore water was balanced. Thus, the hydrogen sulfide in the sediment pore water remained undetected.