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Issue: Catchment scale influences - Land and vegetation condition - Nutrients and sediments - sources and loads

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

Why we need to know about this issue

The degree to which water-borne erosion increases the supply of sediment to rivers can depend on the condition of the land and vegetation. Sediments from soil erosion, often as a result of the removal of riparian and other surrounding terrestrial vegetation, can alter the physical habitat of instream environments by, for example, shallowing of pools or 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.

Erosion and surface runoff can also impact on water quality through increases in suspended solids. Nutrients are transported in suspended solids and these can have their own impacts (see Inland waters: Habitat scale influences: Water Quality (for surface and groundwater): Nutrients).

Catchment erosion and sedimentation can also have the potential for downstream impacts on creeks, rivers, reservoirs, lakes, estuarine and marine environments, as well as terrestrial vegetation and other biodiversity which depends on the water resource.

Indicators

• IW-12 Catchment nitrogen and phosphorus load 
  Quantities of nitrogen and phosphorus concentrating in surface water catchments are a direct measure of this pressure.
• IW-13 Catchment sediment load 
  Sediment loads is a direct measure of the pressure of nutrients and sediments on land and vegetation condition.
• IW-17 Exceedance of turbidity water quality triggers 
  Erosion and surface runoff, can impact on water quality through increases in nitrogen and phosphorus loads. Number of exceedences of water quality triggers for turbidity is a direct measure of this pressure on human water supply.
• IW-18 Exceedance of suspended solids water quality triggers 
  Number of exceedences of water quality triggers for suspended solids is one measure of the likelihood that excess nutrients are being transported.
• IW-24 Extent of sedimentation (incl sand slugs) 
  Nutrients and sediments from soil erosion often as a result of vegetation removal are an indirect indicator of the pressure of land clearing. Nutrients and sediments in turn have the potential for downstream impacts on creeks, rivers, reservoirs, lakes, and estuarine and marine environments, and ultimately on terrestrial vegetation and other biodiversity. Extent of streams and water bodies affected by sedimentation is therefore also a direct measure of the area potentially affected by excess nutrients.
• LD-04 Area and change in area of exposed soil surface contributing to erosion 
  Area of bare soil is a direct indicator for source and a surrogate indicator for the potential load of sediment available for deposition into inland waters.

Related issues

• Inland Waters - Catchment scale influences- Land and vegetation condition- Nutrients and sediments - sources and loads 
• Inland Waters - Habitat scale influences- Water Quality (for surface and groundwater)- Nutrients 
• Inland Waters - Catchment scale influences- Land and vegetation condition- Erosion