Relationship Observed among Loss of Ignition, Oxidation-Reduction Potential and Acid-Volatile Sulfide Content of Surface Sediment from the Seto Inland Sea, Japan

1993～1994年に, 瀬戸内海全域の表層底泥の調査を行った. 1994年4月および6月に比べ, 1993年10月と1994年1月には強熱減量(IL)と酸揮発性硫化物(AVS-S)が高く, 酸化還元電位(Eh)が低かった. これらは1993年夏の多量の降雨による影響を反映しているものと考えられた. 泥の含水率とILの間には明瞭な曲線関係が得られた. また, IL>5%, Eh6%, Eh0. 1mg g^で富栄養状態にあるが, 安芸灘, 伊予灘, 備讃瀬戸, 豊後水道などの瀬戸部はIL+200mV, AVS-Sでそれほど富栄養化していないことが理解された. 最近の20年間に瀬戸内海の水質は次第に改善されてきたようであるが, 今回の結果からは, 底質の改善にはさらに長い時間を要することが伺われる. 水質, 底質とも貧酸素あるいは低酸素状態にさせないことが, 底棲生物を繁栄させ, ひいては生物撹乱による底泥への酸素の供給と食物連鎖を通した物質循環を活発化させる上で重要である.The quality of the surface sediment from the Seto Inland Sea was investigated seasonally during 1993 and 1994. In October 1993 and January 1994, ignition loss (IL), an indicator of organic matter, and the concentration of acid volatile sulfide (AVS-S) showed high values while oxidation-reduction potential (Eh) showed lower values, compared to April and June 1994. The differences of these parameters between two periods indicated the effects of a record heavy rain during the summer of 1993. An apparent curvilinear relationship was observed between water content and IL. Sulfate reduction caused an increase in AVS-S under the conditions of IL > 5 % and Eh 6 %, Eh 0.1 mg g^, while Setos (narrow regions of the inland sea) such as Aki Nada, Iyo Nada, the Bisan Strait and the Bungo Channel are less-eutrophied with IL +200 mV, AVS-S . Although eutrophication of sea water in the Seto Inland Sea seems to have been slightly alleviated during the two recent decades, the results of the present study indicate that improvement of the sediment quality will take a longer time. A suggestion was made that anoxic or hypoxic conditions both in the water and sediments must be prevented so that the condition allows the benthic community to flourish and, in turn, accelerate the removal of organic matter in the sediments due to the supply of oxygen by bioturbation, and stimulation of the material cycling through the food web