Sediment oxygen consumption and vertical flux of organic matter in the Seto Inland Sea, Japan

Vertical flux of organic matter and rates of sediment oxygen consumption (SOC) were measured in summer 2000 at a muddy sediment site (21m depth) in the Seto Inland Sea, Japan. During the 26-day experimental period (15 July to 9 August), a diatom bloom occurred, lasting for about a week. The vertical flux of organic carbon and chlorophyll a (FC and Fchl), measured at 12.5m depth, showed a sharp peak following the development of the bloom. Under these conditions, SOC ranged from 1.4 to 3.0 mmolO2m 2 h 1, and it was strongly influenced by the biomass of macrozoobenthos present in the experimental chambers used for SOC measurements. However, macrozoobenthic oxygen consumption made up only 5% of SOC. SOC variations were not coupled with corresponding changes in FC or Fchl. The effects of other factors, such as water temperature, as well as levels of sediment chlorophyll a and bacterial abundance, were minor, presumably because these parameters did not vary strongly during the study period. The average SOC value corrected for macrozoobenthos oxygen consumption (1.8 mmolO2m 2 h 1) and converted into the decomposition rate of organic material was nearly balanced with the FC averaged over the experimental period (0.7Cm 2 day 1). This indicates that this muddy sediment area in the Seto Inland Sea plays an important role in the degradation of organic material supplied from the water column.