The effects of agricultural practices on acid sulfate soils and nutrient release in groundwater dependent systems of southwestern Australia
Lillicrap, A., Overheu, T., Bell, R.W., Pal, Y. and Price, B. (2012) The effects of agricultural practices on acid sulfate soils and nutrient release in groundwater dependent systems of southwestern Australia. In: Eurosoil 2012: Soil Science for the Benefit of Mankind and Environment. 4th International Congress of the European Confederation of Soil Science Societies (ECSSS), 2 - 6 July, Bari, Italy.
The ecosystems on the coastal plains of south-west Australia (SW WA) (e.g. Swan Coastal plain, Scott River plain) are groundwater dependent. The interactions between surface water and groundwater can greatly influence water quality of these systems. Redox conditions of groundwater can remove nitrate, while evaporation from surface waters can concentrate soluble salts. Acid sulfate soils also widely occur across the coastal plains particularly in wetlands.
Practices associated with agricultural development such drainage, agroforestry and application of fertilisers has altered the natural hydrology, disturbed acid sulfate soils and impacted on water quality. To understand the impact of these practices on acid sulfate soils, nutrient cycling and subsequent effects on water quality for SW WA, a combination of column experiments and monitoring of surface water and groundwater was used. The study sites were located at Torbay, Scott Coastal Plain, Stratham and Peel Harvey area.
The study found acidification of surface water from acid sulfate soils had a limited spatial extent and was confined to disturbed wetlands and the surface runoff from these wetlands. The high acid neutralising capacity of many coastal soils helped to minimise widespread acidification of surface water but salinity impacts from acid sulfate soils disturbance were more dispersed. The depth of the summer watertable was the main determinant of the depth to the sulfidic layer in the acid sulfate soils. Over much of the coastal plain the summer watertable and sulfide layer was below the depth of agricultural drainage. Bluegum plantations can lower watertables thereby exposing acid sulfate soils and causing acidification of groundwater, as well as surface waters.
Acid sulfate soil oxidation formed iron oxy-hydroxides which sorbed phosphorus. The strong reducing conditions of groundwater and soils increases the risk of denitrification but acidification restricted nitrification. Reducing conditions also led to reduction of iron oxides and release of phosphorus into the water column.
The coastal podzols with humic layers led to strong reducing conditions in groundwater where sulfate concentrated by evaporation was reduced to form sulfides. Our results suggest that acid sulfate soils on many parts of the coastal plain resulted from in-situ groundwater processes rather than marine inundation.
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|Murdoch Affiliation:||School of Environmental Science|
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