SUSPENDED-MATTER PARTICLE-SIZE IN SOME WEST-EUROPEAN ESTUARIES .2. A REVIEW ON FLOC FORMATION AND BREAK-UP

The results of particle size measurements in several estuaries with a Coulter counter, by pipette analysis and with a Plankton camera that gives the in situ size are discussed. The in situ size distribution of flocs is probably the result of a complex interaction of processes that induce flocculation. In estuaries, the kinetics of the processes in relation to the tidal cycle are particularly important. There is no evidence for an influence of salinity on in situ floc size distributions. In situ flocs are smaller than the turbulent whirls and probably do not break up after their formation. The floc break-up that occurs during sampling and analysis is an indication of the firmness (strength) of the flocs. The salinity increase at the fresh-saline water contact reduces the floc strength by mobilizing natural polymers (polysaccharides).