Influence of hypersaturated dissolved oxygenated water on the elution of hydrogen sulfide and methane from sediment in the dredged area in polyhaline Lake Nakaumi

Equipment for supplying hypersaturated dissolved oxygen (DO) into water without vertical mixing was installed at a depth of 13.8 m (1 m above the bottom) in the dredged area of polyhaline Lake Nakaumi. The vertical profile of dissolved sulfides, including H2S and HS− (ΣH2S), and the CH4 concentrations in the water column and interstitial water of bottom sediment were investigated monthly during a period when hypersaturated DO water was delivered at a depth of 13.8 m. The area near the bottom was identified as oxic. H2S is easily and rapidly oxidized in an oxic environment through a chemical reaction with DO. Although the concentration of CH4 in the experimental area was 95 % lower than that in the control area, CH4 was detected, even though 20–220 % DO was observed near the bottom, where no H2S was detected. We can therefore confirm that supplying hypersaturated DO can improve the water quality, as well as the ecosystem, by preventing the evolution of H2S.