In-Situ Measurement of Mercury Transport in the Sea Water of Minamata Bay

Two kinds of in-site measurement of mercury transport and transformation were attempted in Minamata Bay. First, we conducted highly-frequent (weekly) water sampling for mercury speciation in sea water with continuous current measurement at an observation tower during summer season. Second, monthly water sampling with measuring the vertical profile of grain size distribution by LISST-100X at three stations in the bay was carried out.As a result of this research, the followings are clarified: i) Particulate and dissolved total mercury (T-Hg) in bottom layer was higher than that in both surface and middle layers; ii) Negative correlation between dissolved T-Hg and methylmercury (MeHg) was shown; iii) Annual particulate T-Hg and MeHg transport from Minamata Bay to the Yatsushiro Sea was estimated as 6 kg and 0.05 kg, respectively; iv) Vertical variation of grain size distribution of SS was not shown in winter, but significantly done in summer; and v) It is possible the source of mercury in bottom layer and surface layer is different.