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Issue: Habitat scale influences - Water Quality (for surface and groundwater) - Sediment and turbidity

This is an issue under the Inland waters theme of the Data Reporting System.

Why we need to know about this issue

Although many of Australia's inland rivers and wetlands have a high natural turbidity, suspended solids can directly affect aquatic organisms and habitats, blocking gills and filter feeders and smothering sedentary aquatic plants, animals and their eggs. Suspended sediment loads in inland waters can have other significant impacts such as siltation of river channels, infilling of wetlands, reduced light penetration inhibiting photosynthesis, shallowing pools and burying coarse bottom sediments leading to a loss of habitat and spawning sites for gravel bed dependent fish. This can produce flow on effects through food chain linkages.

Where the supply of sediment from upstream exceed a river's flushing capacity, this material will accumulate and smother stream bed habitats and fill deep pools. Sand and gravel are too unstable for growth of benthic organisms and loss of deep pools also means a loss of refuge and breeding grounds.

Turbidity is also an indicator of potential nutrient pollution and is an important factor in the development of algal blooms. Nutrients are transported in suspended solids and these can have their own impacts as discussed in Inland waters: Water Quality (for surface and groundwater) - Nutrients . On the other hand, highly turbid water will limit light penetration of the water and in some cases it is light energy rather than nutrients that is the major limiting factor to the development of algal blooms.

There is a close link between land use and levels of suspended material in inland waters.

Indicators

• IW-12 Catchment nitrogen and phosphorus load 
  Nitrogen and phosphorous may can enter waterways via sedimentation. Sediments can disrupt aquatic habitats and increase turbidity. Quantities of nitrogen and phosphorus concentrating in surface water catchments are an indirect measure of this pressure.
• IW-13 Catchment sediment load 
  Sediment can disrupt habitats by bringing with it nitrogen and phosphorous and through increased turbidity. Sediment loads in inland water catchments is one measure of the likelihood of turbidity occurring.
• IW-17 Exceedance of turbidity water quality triggers 
  Turbidity is an indicator of the amount of soil and organic matter suspended in water. Turbidity is also an indicator of potential nutrient pollution (through the suspended material), which is an important factor in the development of algal blooms. Number of exceedences of water quality triggers for turbidity is a direct measure of this pressure.
• IW-18 Exceedance of suspended solids water quality triggers 
  Number of exceedences of water quality triggers for suspended solids is a direct measure of this pressure.
• IW-19 Exceedance of total nitrogen and phosphorus water quality triggers 
  Changes in nitrogen and phosphorus concentrations, through erosion and surface runoff, can impact on water quality. Sediments can transport nutrients. Number of exceedences of water quality triggers for suspended solids is an indirect measure of this pressure.
• IW-24 Extent of sedimentation (incl sand slugs) 
  Soil erosion also has the potential for downstream impacts on creeks, rivers, reservoirs, lakes, and estuarine and marine environments. Water-borne erosion increases the supply of sediment to rivers. Extent of streams and water bodies affected by sedimentation is a measure of the area likely to be affected by turbidity.
• LD-04 Area and change in area of exposed soil surface contributing to erosion 
  Soil erosion also has the potential for downstream impacts on creeks, rivers, reservoirs, lakes, and estuarine and marine environments. Water-borne erosion increases the supply of sediment to rivers. Extent of land subject to erosion is an indirect indicator for the quantity of loose soil available to contribute to turbidity.
• HS-61 Water quality in human settlements 
  Dirty tapwater is also an indicator of excessive turbidity in water sources.