THE FRESH-WATER FLOC - A FUNCTIONAL-RELATIONSHIP OF WATER AND ORGANICAND INORGANIC FLOC CONSTITUENTS AFFECTING SUSPENDED SEDIMENT PROPERTIES

Flocculated fine-grained sediment is a complex matrix of microbial com munities and organic (detritus, cellular debris and extracellular poly mers) and inorganic material. Suspended flocs within any aquatic syste m play a significant ecological role as they can regulate the overall water quality through their physical, chemical and/or biological activ ity. This paper investigates the complex structural matrix of riverine flocs over a large range of magnifications using correlative microsco pic techniques. The significance of floc structural characteristics [( size, shape, porosity, density, inorganic composition, organic composi tion (bacteria and fibrils)] on the physical (eg. transport and settli ng), chemical (eg. adsorbing/transforming contaminants and nutrients), and biological (eg. biotransformation and habitat development) behavi our of a floc is investigated. Results suggest that it is the floc's i nternal structure that has a significant impact on controlling the abo ve floc behaviours. This internal structure is complex and is often do minated by the existence of a three-dimensional matrix of fibrillar ma terial secreted by the active microbial community within the floc. Thi s matrix, in conjunction with the inorganic and bioorganic (active and inactive) constituents of a floc, provides an intricate pore structur e that may result in water being an important bound component of a flo c. These complex interactive structural and functional properties of a flee are considered to influence a floc's behaviour both physically i n how it is transported or settled, chemically in how it adsorbs/trans forms contaminants and nutrients, and biologically in how it develops a diverse microhabitat capable of modifying the structural, chemical a nd biological makeup of the floc.