Prolonged recovery of acid sulfate soils with sulfuric materials following severe drought: causes and implications

作者：Mosley L M^*; Biswas T K; Cook F J; Marschner P; Palmer D; Shand P; Yuan C; Fitzpatrick R W

来源：Geoderma, 2017, 308: 312-320.

DOI：10.1016/j.geoderma.2017.03.019

• Add sulfate soils
• Pyrite
• Acid drainage
• Drought
• Climate change
• River Murray

Pyrite in acid sulfate soils can get oxidised during drought resulting in severe soil and water acidification (pH <4). The frequency and severity of drought and flooding is increasing in many regions of the world due to climate change but there has been limited research on the ability of acid sulfate soils to recover from these events. We studied the recovery of heavy clay soils in the Lower Murray River (South Australia) irrigated agricultural areas over a 5 year period (2011-2015). The heavy clay acid sulfate soils in this region dried, cracked and acidified due to river and groundwater levels falling by nearly 200 cm during the 2007-2010 severe "Millennium" drought followed by reflooding events between 2011 and 2015. Approximately 300 cm deep soil cores were collected from three locations along a transect in 2011, 2012, 2013, and 2015. The soil properties measured were pH, reduced inorganic sulfur (RIS, pyrite), titratable actual acidity (TAA), retained acidity, and acid neutralising capacity. Soil pH showed very little change over the post-drought period with a very acidic (pH 3.5-4.5) layer at approximately 100-225 cm depth in all three soil profiles. In this acidic layer there also were substantial amounts of TAA (up to 200 mol H+ tonne(-1) dry weight) and retained acidity (up to 70 mol H+ tonne(-1) dry weight) in the form of the Fe oxyhydroxy sulfate mineral jarosite. There was limited reformation of RIS. To assess why the sulfuric material in the acid sulfate soils has not recovered post-drought we conducted (i) laboratory incubation experiments with and without organic matter amendment, and (ii) modelling of the flushing of acidity from the soil due to irrigation, rainfall and drainage. Based on the field and laboratory results the causes of slow recovery appear to be: (i) lack of available organic carbon and too low a pH to enable microbial reduction reactions that generate alkalinity, ii) slow flushing of acidity due to the low hydraulic conductivity in the heavy clay layers with the main zone of below the drain depth, and (iii) slow dissolution of the sparingly soluble jarosite mineral, which is likely buffering the sub-surface soil layers at approximately pH 4. The implications are that acid sulfate soils with sulfuric materials have long recovery times following droughts and impacts are likely to increase in the future.

• 出版日期2017-12-15
• 单位CSIRO