Sedimentation, in estuaries

The accumulation of sediments in estuaries appears to be so effective that Meade (1981) has estimated that, "Probably less than 5 percent of all river sediment discharged into the tidal waters of the Atlantic seaboard is deposited on the floor of the continental shelf or the deep sea". These sediments contain an often dramatic imprint of human activity and impact on the estuary and its watershed. But it is an imprint which results not only from the input of materials, but also from the interaction of a great variety of physical, chemical and biological processes in the estuary. We are only beginning to learn to read that record, but the early results suggest that we may learn more about what flows between rivers and the sea from the humble muds on the estuary floor than we can from the water above. 

Microbial mats and biofilms, defined as surface layers of microbes entrained in a matrix of extracellular polymeric substances (EPS) (Characklis and Marshall, 1989), are also important in changing the surface texture and erodibility of sediments in estuaries (de Beer and Kiihl, 2001). The EPS are primarily composed of cellular-derived polysaccharides, polyuronic acids, proteins, nucleic acids, and lipids (Decho and Lopez, 1993 Schmidt and Ahring, 1994). The EPS can serve as a cementing agent for surface sediment particles, thereby affecting the erodibility of sediments as well as the flux of dissolved constituents across the sediment-water interface (de Beer and Kiihl, 2001). 

The four dominant processes controlling movement of sediments in estuaries are as follows (1) erosion of the bed (2) transportation (3) deposition and (4) consolidation of deposited sediments. 

Microbial mats and biofilms, defined as surface layers of microbes entrained in a matrix of EPS, are also important in changing the surface texture and credibility of sediments in estuaries. 

Krone, R.B. (1962) Flume studies of the transport of sediment in estuarial shoaling processes. Univ. of California, Hydraulics and Engineering Lab. and Sanitarian Engineering Research Lab. Berkeley, pp. 110. 

Meade, R.H. (1969) Landward transport of bottom sediments in estuaries of the Atlantic coastal plain. J. Sed. Petrol. 39, 222-234. 

During the 1994-1995 austral summer, samples of sediments fron Potter Cove were collected in order to assess the presence and origin of Cd, Cr, Cu, Fe, Mn, Pb and Zn. Numerous studies have shown that finer fractions of sediments and finer textured sediments in estuaries and marine zones have higher levels of Fe and Mn oxides and trace metals than those found in coarse materials (43). The water movement in the cove is usually by clockwise currents with the littoral current on the southern coast favouring the sedimentation of the finer particles (<62 pm) from a 10 m depth. Table 6.4 and Figure 6.3 show the granulometric composition... 

Hopner, T. and Orliczek, C. (1978). Humic matter as a component of sediments in estuaries. In Biogeochemistry of Estuarine Sediments. UNESCO, Paris, pp. 70-74. 

Krone, R.B. 1962. Flume Studies of the Transport of Sediment in Estuarial Processes. Final Report, Hydraulic Engineering Laboratory and Sanitary Engineering Research Laboratory, University of California, Berkeley. 

Sediments from the bottom of streams, rivers, lakes, estuaries, and oceans are collected with a bottom grab sampler or with a corer. Grab samplers are equipped with a pair of jaws that close when they contact the sediment, scooping up sediment in the process (Figure 7.5). Their principal advantages are ease of use and the ability to collect a large sample. 

Koehnken, L. (1990). The composition of fine-grained weathering products in a large tropical river system, and the transport of metals in fine-grained sediments in a temperate estuary, Ph.D. thesis, Princeton University, Department of Geological and Geophysical Sciences. 

Estuaries exhibit physical and chemical characteristics that are distinct from oceans or lakes. In estuaries, water renewal times are rapid (10 to 10 years compared to 1 to 10 years for lakes and 10 years for oceans), redox and salinity gradients are often transient, and diurnal variations in nutrient concentrations can be significant. The biological productivity of estuaries is high and this, coupled with accumulation of organic debris within estuary boundaries, often produces anoxic conditions at the sediment-water interface. Thus, in contrast to the relatively constant chemical composition of the... 

Li YH, Chan LH (1979) Desorption of Ba and Ra from river-borne sediments in the Hudson estuary. Earth Planet Sci Lett 43 343-350... 

Removal to sediments. Removal of surface-reactive trace elements from the oceans readily occurs by adsorption onto settling particles, and this process is most pronounced in the typically high-energy, particle-rich estuarine environment. Particles are supplied by rivers, augmented by additions of organic material generated within the estuary. Also, floes are created in estuaries from such components as humic acids and Fe. The interaction between dissolved and colloidal species is enhanced by the continuous resuspension of sediments in... 

Borole DV, Krishnaswami S, Somayajulu BLK (1977) Investigations on dissolved uranium, silicon and on particulate trace elements in estuaries. Estuarine Coastal Mar Sci 5 743-754 Borole DV, Krishnaswami S, Somayajulu BLK (1982) Uranium isotopes in rivers, estuaries and adjacent coastal sediments of western India their weathering, transport and oceanic budget. Geochim Cosmochim Acta 46 125-137... 

Lapointe BE, O Coimell JD, Garrett GS (1990) Nntrient conphngs between on-site sewage disposal systems, groundwaters, and nearshore surface waters of the Florida Keys. Biogeochem 10 289-307 Li Y-H, Chan L-H (1979) Desorption of Ba and Ra from river-borne sediments in the Hudson estuary. Earth Planet Sci Lett 43 343-350... 

The relative toxicity of organotin compounds to alga Scenedesmus obliquus is shown in Table 12. Pettibone and Cooney investigated the toxicity of methyltins (MMT MeSnCl3 DMT Me2SnCl2 and TMT Me3SnCl) to microbial populations in estuary sediments in... 

Sanders, J.G. and G.R. Abbe. 1987. The role of suspended sediments and phytoplankton in the partitioning and transport of silver in estuaries. Contin. Shelf Res. 7 1357-1361. 

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