It should be noted that this data is now somwhat dated!
Streams draining through areas of acid soils are at risk from acidification
through mobilisation of H+ ions out of the acid soils and into the drainage
network.
This is a catchment scale problem, which requires property scale management
and planning.
River acidity is sensitive to catchment scale changes that influence the
spatial pattern of runoff contributions, particularly the proportioning
between acid and more neutral soils.
The indicator distinguishes catchments on the basis of percent of catchment
river length draining acid soils.
Areas characterised by a high percentage of rivers draining acid soils are
likely to have more acidic stream water than areas where only a small
proportion of rivers drain acid soils.
The indicator has not been validated against river pH. Acid soils are defined
as those having a pH of 4.8 or less (measured in CaCl2).
The reliability of the ASRIS data set is unknown, as very little validation
has been done.
We assume here that it is poor, given the enormous spatial heterogeneity of
soils.
Reliability of the national rivers coverage is good for the purposes of this
assessment.
Variation in the pH of rivers and streams is recognised as an important driver
of aquatic biota.
River pH data are not available for the nationes rivers; even exceedance data
at the AWRC scale is patchy.
None-the-less there was a need to produce a credible synoptic map for
Australia using existing data.
surrogate measure was developed using soil type and stream location data.
Streams draining through acid soils are at risk from acidification through the
mobilisation of hydrogen anions, out of the acid soils into streams.
Surface soils can be naturally acid or can be acidified through the
introduction of legumes or application of fertilisers.
Sub-soils and groundwaters can also be acidic and these can leak into streams
as a result of upward mobilisation of waters or gullies formed through water
erosion.
The indicator was compiled by overlying soils of low acid buffering capacity
(the soil pH layer of ASRIS) with rivers (from AUSLIG Topo250K national rivers
coverage) and areas of cropping and improved pasture (National Land-use Map).
The indicator has not been validated against stream data. The different map
scales gave a similar picture.
Interestingly, the patterns for stream acidification are similar to those of
the 2050 salinity map.
Predicted high acidification of streams is prominent in the wheat belt in WA
(including Albany Coast, Frankland, Blackwood, Preston, Avon, Swan Coast,
Moore-Hill, Greenough River basins).
In S the main acidification areas include the Fleurieu Peninsula, Gawler,
Wakefield, Broughton River basins, and Kangaroo Island.
Parts of the Murray-Darling Basin in the>500mm rainfall zone (especially the
Broken, Campaspe River basins) show an elevated acidity hazard.
Some parts of Tasmania also show problem areas (particularly King Island).
Stream acidification is not indicated as a problem in northern Australia.
Data are available as:
- continental maps at 5km (0.05 deg) cell resolution for the ILZ;
- spatial averages over CRES defined catchments (CRES, 2000) in the ILZ;
- spatial averages over the AWRC river basins in the ILZ.
See further metadata for more detail.
