WIND-INDUCED AND TIDE-INDUCED RESUSPENSION OF SEDIMENT AND MICROPHYTOBENTHOS FROM TIDAL FLATS IN THE EMS ESTUARY

The resuspension of microphytobenthos (mainly benthic diatoms) and mud (< 55-mu m fraction) from tidal hats was studied in the Ems estuary (Netherlands/Germany, of which similar to 50% is covered by intertidal areas. Mud and microphytobenthos are resuspended simultaneously from the tidal flats in the estuary. The concentrations of these parameters in the main channels of the estuary are strongly affected by erosion due to wind-induced waves and by settlement during calm weather conditions. The resuspension of mud can be described as a linear function of the ''effective windspeed,'' which is defined as the windspeed averaged over three high-water (6 h bracketing high water) periods preceding sampling. The resuspended fraction of microphytobenthos from the top 0.5-cm layer of sediment can also be described as a linear function of the effective windspeed. Our data indicate that for this estuary, the proper quantification of resuspension of mud and microphytobenthos requires consideration of relatively large areas.