SEDIMENT OXYGEN-DEMAND IN HIROSHIMA BAY

Effects of environmental factors, depth and layer thickness of sedimen t, organic matter, reducing substance, oxygen concentration and temper ature, on sediment oxygen demand(SOD) were examined by laboratory expe riments. Apparent effects on the SOD rates were recognized from each f actor, except for the layer thickness and organic matter content in se diment. The SOD rates varied with sediment depths, which was attribute d to the reducing substances in sediments. Temperature (T) revealed th e most marked effect among these factors, and SOD rates increased line arly with temperature in the range of 10-30 degrees C. Oxygen concentr ation in overlying water did not influence the SOD rate when it was ov er 2-3 mg/l, but influenced below this concentration. The SOD rates in Hiroshima Bay, measured by both an in situ chamber (bell jar) and a l aboratory method with intact cores, agreed well with each other and ra nged from 0.10 to 0.61 g O-2/m(2)/d, with a mean of 0.3-0.4 g O-2/m(2) /d on an annual basis. The rates in summer and autumn were twice those in winter, It also became evident in this study that SOD rates in Hir oshima Bay were mainly controlled by biological consumptions from summ er to autumn and by chemical consumption of the reducing substances du ring winter and spring.