Soil acidity/Acid Sulfate Soils - 2006Home | Land | Land Use & Management | Soil Acidity/Acid Sulfate Soils | 2006 What does the Data tell us for 2006Acid sulfate soil is the common name given to soils containing iron sulfides. When the sea level rose 10 000 years ago, it inundated the land and sulfate from the sea water mixed with land sediments containing iron oxide and organic matter. The subsequent chemical reaction produced large amounts of iron sulphides in the waterlogged sediments. When these sediments are exposed to air, the sulphides in them oxidise to produce sulfuric acid and then acid sulfate soils. The figure below illustrates how acid sulfate soils develop when land is modified, particularly through artificial drainage. A map illustrating the distribution of acid sulfate soils can be viewed at http://gis.shoalhaven.nsw.gov.au/soemaps
Natural Setting - low frequency, low magnitude, short duration
acidity Post Drainage - High frequency, high magnitude, persistent acidity
Sourced from NSW Department of Primary Industrieshttp://www.ricecrc.org/reader/soil-acidss/acid-intro.htmIn Shoalhaven, most acid sulphate soil areas are located in and around the coastal floodplain. The presence of Coastal Acid Sulfate Soils (CASS) can lead to water pollution when toxic levels of elements such as Aluminium and Iron are released into waterways. This is often evidenced by fish kills but acidified water also impacts on other aquatic plant and animal species. Acid water can also affect aquatic habitat when mixed with less acid stream water, resulting in iron precipitating and smothering plants and the streambed. In Shoalhaven, Acid Sulfate Soils are problems in and the Shoalhaven River Floodplain, particularly Broughton Creek. The Shoalhaven River is one of the largest on the south coast of NSW. The river is only intermittently open at Shoalhaven Heads. The majority of time, the river flows through Berry’s canal, a man-made canal that was constructed by Alexander Berry in 1822, and terminates at Crookhaven Heads. The lower-lying land near the Shoalhaven River is made up of a deltaic-estuarine plain, which has now been significantly drained and due to the soils high organic content, is used for pasture grown for cattle (dairy or beef). However the draining of this land has lead to exposure of acid sulfate soils that have lead to water quality problems causing fish kills often during rain events that follow a drought or low rainfall period. The Broughton Creek-Shoalhaven floodplain was identified as an area greatly affected by CASS, and has been researched for many years (Pease 1994; Blunden 2000; Glamore 2003) with numerous management options tested and implemented including floodgates, smartgates and permeable reactive barriers. On the southern side of the Shoalhaven River, the Crookhaven River Floodplain has several large and many small natural drainage basins, most of which are artificially drained. In this area Worrigee, West Pyree and Ryan’s Lane are the highest risk areas for Acid Sulfate Soils. Some of the management options to address the potential for soil and water degradation in this area include the use of floodgates to control drainage and allow tidal water to neutralise acidity, along with a more general acid sulfate soil management options avoiding the exposure of potential acid sulfate soils in the first instance.
Crookhaven River - Drain - Brundee Swamp showing acid affected soils in the foreground
Figure 1 Morphology of the Shoalhaven-Crookhaven Flood Plain (Umitsu et al. 2001)
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