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Home > Coastal and floodplains > Estuaries > Factsheets > Water Quality

Estuaries in NSW

Estuarine Water Quality

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Bottom Sediments

Estuarine bottom sediments may be considered as both a sink and a source for many pollutants, including nutrients, heavy metals and a large number of organic compounds (Skei, 1992; Calmano et al, 1992; Day et al, 1989). Many substances have a high affinity for small suspended particles of organic or mineral origin, which enter the bottom sediments of estuaries through flocculation and passive settling, and dissolved substances which re-enter the water column through resuspension, bio-geochemical transformations, diffusion and bioturbation (Skei, 1992).

An important factor to consider is the proportion of a substance that is biological inert (usually sediment-bound) and so not immediately available for uptake by organisms (Batley, 1987; Calmano et al, 1992). Such pollutants may have little effect on biota, particularly if they are buried below the oxygenated surface layer, but may be reactivated by bioturbation or human disturbance.

Sediment pollution "hot spots" are often the result of an identified source, such as a metal smelter or sewage outfall. The management of heavily polluted sediments requires an appraisal of the risks and costs involved in the various options, which include leaving them undisturbed, capping with a clean layer, chemical treatment, and dredging for disposal at another site (Skei, 1992).

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