Estuaries accumulate soil and plant material from both the catchment and internal sources (for example decomposing plants and algae). These sediments can bind nutrients and other contaminants, which may be released under certain conditions. The sediments therefore can act as either a sink or source of nutrients to the overlying water. They can also be responsible for low oxygen events.
Over a number of years Department of Water staff, working with Geoscience Australia, have developed ways of using sediment information as an indicator of the condition of the estuary. Attributes, such as the ability to bind phosphorus so that it is not available for algal growth, denitrification, oxygen consumption and percent organic matter, are important in assessing estuarine health.
As a key component of assessing estuarine health, sediment studies have been conducted in most estuaries on the South Coast of WA such as Wilson, Parry, Irwin, Walpole Nornalup, Torbay, Wellstead, Beaufort, Gordon, and Stokes Inlets and Oyster and Princes Royal Harbours. Hardy and Leschenault Inlets along with the Vasse Wonnerup, Peel Harvey and Swan Canning estuaries have now been included.