EFFECTS OF SPILLED AND STRANDED OILS ON SEAWATER INFILTRATION AND MACROBENTHIC COMMUNITY IN TIDAL FLATS

Abstract

Effects of spilled oil stranded on tidal flats on macrobenthic community were studied using a tidal flat ecosystem simulator. Two simulators, C simulator as a control and O simulator with oil spill by fuel oil C (1 lm-2), were compared. Total population density of macrobenthos in the C simulator increased and was kept high throughout the experimental period. In the O simulator, however, the population density of macrobenthos was kept low from the oil spill treatment until day 35 and thereafter recovered significantly. ORP in both the C and Osimulators showed positive values in the top 1 cm layer of sediments before the oil spill treatment. However ORP of the top 1cm of the sediment in the O simulator dropped down to negative values after the oil spill. The volume of seawater infiltration in the O simulator in day 23 decreased to a third by the spill. However, it recovered back to almost the same volume as that before the spill in day 58 when macrobenthic population density also recovered. Also, the concentrations of fuel oil C in top 1 cm of the sediments decreased gradually down to a half. The removal of fuel oil C in sediment by washout through tides and waves are possibly responsible for the recovery of seawater infiltration, consequently resulting in the restoration of macrobenthic community in the O simulator. These results suggest that spilled oil on tidal flats apparently reduces the infiltration volume of seawater and causes the development of reductive zone in sediment layer and such changes in physical environment are mainly responsible for the damages in the macrobenthic community in tidal flats.