Sediment is present in the marine environment as
both suspended and deposited particles and comprises
both organic and inorganic components. The extent
to which particles are suspended or deposited is
a function of their density and the hydrodynamics
of the water column.
Suspended sediment influences the effects of some
non-toxic substances such as nutrients by reducing
light penetration and preventing uptake by primary
producers. This allows nutrient concentrations to
increase while eutrophication effects are not apparent.
Some toxic substances have an affinity for sediments,
in particular organic particles, and the presence
of suspended sediments can reduce water column concentrations
here, but the toxic substance may still be biologically
available, e.g. to sediment feeders/dwellers.
Sediment type is critical, not only because of
its role in determining the faunal community, but
also because of its role in adsorbing pollutants.
In general terms, fine mud/silt/clay sediments with
high organic content retain more contaminants than
relatively coarse sandy sediments. The smaller the
particle size, the more likely sediments are to
retain contaminants which may subsequently be released
back into the water column.