Estimation of microphytobenthic resuspension fluxes in a shallow lagoon in Hokkaido, Japan

We conducted field sampling in a subarctic shallow lagoon (Hichirippu Lagoon) in the eastern part of Hokkaido, Japan. We investigated the chemical composition of the water column, sediment, and sinking particles collected by the sediment trap. The standing stock of chlorophyll a (Chl-a) in the water column and surface sediment were 0.4 to 9.3 and 35.9 to 184 mg m , respectively. Using stable isotope analysis, the contribution rate of microphytobenthos to the sinking particles was found to range from 63 to 74%. The average Chl-a content in the sinking particles was significantly lower than that of the water column. Our results suggest that the contribution of phytoplankton present in the water column to the Chl-a collected in the traps is likely to be negligible. We assumed that the Chl-a fluxes obtained in this study were microphytobenthic resuspension fluxes. The daily flux of Chl-a accounted for 47.0 to 1,270% of the total standing stock of Chl-a in the water column. The mean relative percentage of daily Chl-a flux divided by the standing stock of Chl-a in the sediment was 6.5%, which indicates that approximately 7% of the microphytobenthos present in the sediment was resuspended, and 93% of the total succeeded at escaping the winnowing action. Although the resuspension phenomenon had little effect on the population of microphytobenthos, the resuspended microphytobenthos had a major impact on the total micro algal biomass in the water column. This is the first direct estimate of microphytobenthic resuspension flux in shallow estuaries.