The Freshwater Floc: A Functional Relationship of Water and Organic and Inorganic Floc Constituents Affecting Suspended Sediment Properties

Abstract

Abstract. Flocculated fine-grained sediment is a complex matrix of microbial cmnmunities and organic (detritus, cellular debris and extracellular polymers) and inorganic material. Suspended floes within any aquatic system play a significant ecological role as they can regulate the overall water quality through their physical, chemical and/or bioloocal activity. This paper investigates the complex structural matrix of nverine floes over a large range of magnifications using correlative microscopic techniques. The significance of floc structural characteristics [(size, shape, porosity, density, inorganic composition, organic composition (bacteria and fibrils)] on the physical (eg. transport and settling), chemical (eg. adsorbin~transfolqning contaminants and nutrients), and biological (eg. biotransfornmtion and habitat development) behaviour of a floc is investigated. Results suggest that it is the floc's internal structure that bm~; a significant impact on controlling the above floc behaviours. This internal structure is complex and is often dominated by the existence of a three-dimensional matrix of fibnllar material secreted by the active microbial conmmnity within the floc. This matrix, in conjunction with the inorganic and bioorganic (active and inactive) constituents of a floc, provides an intricate pore structure that may result in water being an important bound component of a floc. These colnplex interactive structural and functional properties of a floc are considered to influence a floc's behaviour both physically in how it is transported or senled, chemically in how it adsorbs/transforms contaminants and nutrients, and biologically in how it develops a diverse microhabitat capable of modifying the structural, chelnical and biological makeup of the floe.

Composite suspended sediment particles and flocculation in glacial meltwaters: preliminary evidence from Alpine and Himalayan basins

“…In contrast, Figure 3f shows a composite form with a much looser overall structure (and a smaller range of constituent grain sizes) with large voids that may be indicative of formation solely by flocculation within the proglacial stream. In the absence of organic binding agents [see Droppo et al (1997)], the composite particles shown in Figure 3a, c and f, the upper part of figure 3b, and the outer section of figure 3e, may result solely from electrochemical flocculation processes. To the authors' knowledge, this mechanism of floc formation has not been reported previously in the freshwater fluvial environment.…”

“…Continuous in situ measurement of such events using a field-portable laser backscatter probe, such as that described by Phillips and Walling (1995), would allow such controls to be explored further. In addition, monitoring the downstream passage of a glacially sourced suspended sediment pulse may provide further insights into freshwater flocculation processes (including electrochemical mechanisms), since both the proportion of organic matter and bacterial activity are likely to increase downstream; see Petticrew, (1996) and Droppo et al (1997). Equally, information on the mineralogy, structure and abundance of source-derived aggregated suspended particles may provide insights into the nature of the sub-glacial drainage system and sediment sources; see Eyles (1978), Collins (1979Collins ( , 1989, and Foster et al (2000).…”

“…These particles enter the fluvial system in an aggregated form and retain that structure during transport (Walling and Woodward, 2000). In contrast, flocs are composite particles that have formed within the water column due to various physical, chemical and/or biological processes (Petticrew, 1996;Droppo et al, 1997). Aggregates may be incorporated into flocs and each may break up to produce smaller composite and discrete particles.…”

It's sedimentary, my dear Watson : implications of watershed processes on the sediment fingerprinting approach

“…In its simplest form, the term can refer to the primary mineral particles (e.g., sand, silt, clay), however, much of the soil is moved as aggregates which are a cohesive agglomeration of both inorganic and organic matter, which may have different physical and biogechemical characteristics in comparison to the primary particles of which they comprise (Buffle and Leppard 1995a;Buffle and Leppard 1995b;Droppo et al 1997;Droppo 2001). Therefore, making conclusions about the mobilization and transport of sediment based on absolute (i.e., physically and/or chemically dispersed) particle size distribution may result in errors as soil moves as aggregates and, therefore, the effective or aggregate particle size distribution may be more informative .…”

“…Flocculation refers to aggregation of living and non-living biological material and mineral particles that can occur within the water column (Droppo et al 1997). …”