RHEOLOGICAL PROPERTIES OF SEDIMENT SUSPENSIONS FROM ECKERNFRDE AND KIELER FRDE BAYS,WESTERN BALTIC SEA

1 INTRODUCTION Fluid mud is defined as a dense suspension of fine-grained sediment particles averaging in density between 1.03 to 1.30 g/cm3 and between 10 to 480 g/l in concentrations by weight (Ingliss and Allen, 1957). It overlies a substrate of densit…     

RHEOLOGICAL PROPERTIES OF SEDIMENT SUSPENSIONS FROM ECKERNF(O)RDE AND KIELER F(O)RDE BAYS, WESTERN BALTIC SEA

Local areas of fine-grained organic-rich sediments in Eckernforde and Kieler Forde Bays may experience disturbances which cause fluidization of the substrate and create a dense suspension （fluid mud） which exists temporarily as a component of the benthic boundary layer before becoming incorporated into the permanent bottom. Laboratory studies indicate this material behaves rheologically as a non-Newtonian substance, and both shear thinning （pseudoplastic） and shear thickening （dilatant） flow behavior can occur （ofien within the same sample） under low to intermediate shear stresses （2 - 40 Pa） and shear rates （0.46 - 122.49 s^-1）. Detailed granulometric analyses （1/4 phi intervals） of the fraction 〈63 μm show differences in the silt/clay ratio （clay 〈2 μm） between the two environments. Little change in the silt/clay ratio is seen in the Kieler Forde sediments （from 0.74 to 0.95）; however, at Eckernforde, the ratio changed from 0.73 to 2.19. Fine silt particles are lacking or were removed from the 4 to 16 μm fraction of the Eckernforde but not from the Kieler Forde sediments. Both shear thickening and shear thinning flow was observed in the Eckernforde sediments. Shear thickening flow behavior was not observed in the Kieler Forde sediments. Samples of organic-rich （10 to 20%） interface sediments from both areas were analyzed rheologically prior to, and atier removal of organic matter by H2O2 treatment. Reduction in ‘apparent＇ viscosity occurred through the entire range of shear rates and stresses, shear thickening behavior was reduced or became nonexistent, and yield stress decreased significantly compared to the natural samples. The differences in yield stress and flow behavior of dense suspensions result primarily from differences in grain size distributions but the role of organic matter on those properties is very significant and adds to the effects of the grain size distribution of the sediment.