Indicators of Catchment Condition in the Intensive Land Use Zone of Australia – Rivers in acidification hazard

\n\nIt should be noted that this data is now somwhat dated!\n\nStreams draining through areas of acid soils are at risk from acidification\nthrough mobilisation of H+ ions out of the acid soils and into the drainage\nnetwork.\n\nThis is a catchment scale problem, which requires property scale management\nand planning.\n\nRiver acidity is sensitive to catchment scale changes that influence the\nspatial pattern of runoff contributions, particularly the proportioning\nbetween acid and more neutral soils.\n\nThe indicator distinguishes catchments on the basis of percent of catchment\nriver length draining acid soils.\n\nAreas characterised by a high percentage of rivers draining acid soils are\nlikely to have more acidic stream water than areas where only a small\nproportion of rivers drain acid soils.\n\nThe indicator has not been validated against river pH. Acid soils are defined\nas those having a pH of 4.8 or less (measured in CaCl2).\n\nThe reliability of the ASRIS data set is unknown, as very little validation\nhas been done.\n\nWe assume here that it is poor, given the enormous spatial heterogeneity of\nsoils.\n\nReliability of the national rivers coverage is good for the purposes of this\nassessment.\n\nVariation in the pH of rivers and streams is recognised as an important driver\nof aquatic biota.\n\nRiver pH data are not available for the nationes rivers; even exceedance data\nat the AWRC scale is patchy.\n\nNone-the-less there was a need to produce a credible synoptic map for\nAustralia using existing data.\n\n surrogate measure was developed using soil type and stream location data.\n\nStreams draining through acid soils are at risk from acidification through the\nmobilisation of hydrogen anions, out of the acid soils into streams.\n\nSurface soils can be naturally acid or can be acidified through the\nintroduction of legumes or application of fertilisers.\n\nSub-soils and groundwaters can also be acidic and these can leak into streams\nas a result of upward mobilisation of waters or gullies formed through water\nerosion.\n\nThe indicator was compiled by overlying soils of low acid buffering capacity\n(the soil pH layer of ASRIS) with rivers (from AUSLIG Topo250K national rivers\ncoverage) and areas of cropping and improved pasture (National Land-use Map).\n\nThe indicator has not been validated against stream data. The different map\nscales gave a similar picture.\n\nInterestingly, the patterns for stream acidification are similar to those of\nthe 2050 salinity map.\n\nPredicted high acidification of streams is prominent in the wheat belt in WA\n(including Albany Coast, Frankland, Blackwood, Preston, Avon, Swan Coast,\nMoore-Hill, Greenough River basins).\n\nIn S the main acidification areas include the Fleurieu Peninsula, Gawler,\nWakefield, Broughton River basins, and Kangaroo Island.\n\nParts of the Murray-Darling Basin in the>500mm rainfall zone (especially the\nBroken, Campaspe River basins) show an elevated acidity hazard.\n\nSome parts of Tasmania also show problem areas (particularly King Island).\nStream acidification is not indicated as a problem in northern Australia.\n\nData are available as:\n\n * continental maps at 5km (0.05 deg) cell resolution for the ILZ;\n * spatial averages over CRES defined catchments (CRES, 2000) in the ILZ;\n * spatial averages over the AWRC river basins in the ILZ.\n\nSee [further metadata](http://data.daff.gov.au/anrdl/metadata_files/pa_iccilr9ab\n__07621axx.xml) for more detail.\n\n