We carried out a demonstration experiment using the Intertidal Flat Experimental Facility (IFEF), which is a semi-closed and experimental intertidal flat ecosystem, to investigate the effects of hypoxia and hydrogen sulfide (H_2S) water on organisms and water quality. We created three tide pools on the experiment tidal flat and divided them into three experiment areas : one area where sodium sulfide (Na_2S) was added to examine the effect of hypoxic water alone; another area where hydrogen chloride (HCl) and sodium sulfide (Na_2S) were added to examine the effect of both hypoxic and hydrogen sulfide (H_2S); and a control area where nothing was added. Then we observed changes in the water quality and the survival situation of the benthic organisms in each area. The results indicated a possibility that the mortality of organisms increases due to a combination of factors, i.e. hypoxic water and high hydrogen sulfide and high water temperature (>20℃). The results also suggested a possibility that in a tidal flat, where the sea level changes frequently, the length of time that organisms are exposed to two factors, i.e. hypoxic water and high hydrogen sulfide, is short, and therefore the mortality can be avoided.
