A COMPARATIVE METALS PROFILE OF HIGASHIYOKA AND KAWAZOE SEDIMENTS OF ARIAKE BAY, JAPAN

Ariake Bay is one of the most important bays in Japan; since it comprises about 40% of the total production of shellfish and Nori (seaweeds) culture growth in there. It is located in the north of Kyushu, and surrounded by four prefectures (Saga, Nagasaki, Fukuoka and Kumamoto). Our former studies suggested a high concentration of metals at Higashiyoka area (station 1), located at vicinity of rivers, and Kawazoe area (station 2), located at mouth of rivers. Therefore, accumulations of metals (Al, As, Cd, Cr, Cu, Fe, Pb, Mn, Hg, Sr, Sn, and Zn) in these areas since the last few decades were studied. The concentration of metals at these stations were in order; station1>station 2. The main studied components of the sediments were Al, Fe, Acid Volatile Sulfide (AVS), Total nitrogen (T-N) and Total Organic Carbon (TOC). The higher concentrations of metals at station 1 were due to high concentrations of these components which control the accumulation of metals more effectively than at station 2. The TOC/AVS ratios were, 0.41 % (station 1) and 0.26 % (station 2). A significant decomposition percentage at station 1 suggests a favorable decomposition of organic matter to sulfides in the sediments and contrariwise at station 2. Meanwhile, the maximum AVS concentrations in the surface sediments of the station 1 reflect the formation of stable metal sulfides. Furthermore, station 1 has high correlations between metalsʹ concentrations as compare to station 2, suggested that metals may have the same source, and/or the same chemical properties as stated in the HSAB (Hard Soft Acid Base Theory). So, Al and Fe, which are hard metals, were shown to accumulate Cr, Sr and other metals of the same hard nature. Also, minor components (Cd, Cu, Pb and Zn) were accumulated together for their similar chemical property as border metals. On the other hand, the poor correlation between As, Sn and Hg, with other studied metals, suggested that these metals might be released by some point source rather than the natural one. The TOC/T-N ratios were more than 8 but less than 12 at these stations; suggest a terrestrial source for organic matter induction caused by anthropogenic activities. The EF values of metals at these stations were higher than 1 but less than 3, suggesting a minor enrichment.