EXPERIMENTS ON RESUSPENSION OF NATURAL MICROPHYTOBENTHOS POPULATIONS

Laboratory experiments on resuspension of benthic diatoms were performed in 1988 on intact cores of sediment obtained from two transects in the Ems estuary (Dutch Wadden Sea, NW Europe). Diatoms were most abundant in sediment from sheltered stations. In the experiments, which were performed in a small carousel system, the percentage of resuspended diatoms increased concomitantly with angular velocity of the agitating paddles. Maximum microphytobenthos resuspension in terms of cell numbers was up to 45% of the total population present in the 0.5-cm top layer, and up to 11% in terms of chlorophyll a. Maximum sediment resuspension was 6%. The results show that the presence of a diatom film (numerous cells on the sediment surface) increases sediment stability, thereby suppressing resuspension of sediment and diatoms. However, if the sediment contains many fine particles and much detritus, sediment stability decreases, leading to increased resuspension. These results support the contention that low detritus content and large numbers stabilize the surface layer of tidal flats, whereas high detritus content and fewer cells (< 2 x 10(5) cm-2) do not. The stabilization is thought to be dependent on a combination of differences in sediment consolidation and in bottom roughness caused by the presence or absence of diatom films.