Porewater geochemistry of inland acid sulfate soils with sulfuric horizons following postdrought reflooding with freshwater

Following the break of a severe drought in the Murray-Darling Basin, rising water levels restored subaqueous conditions to dried inland acid sulfate soils with sulfuric horizons (pH <3.5). Equilibrium dialysis membrane samplers were used to investigate in situ changes to soil acidity and abundance of metals and metalloids following the first 24 mo of restored subaqueous conditions. The rewetted sulfuric horizons remained severely acidified (pH ∼4) or had retained acidity with jarosite visibly present after 5 mo of continuous subaqueous conditions. A further 19 mo of subaqueous conditions resulted in only small additional increases in pH (∼0.5-1 pH units), with the largest increases occurring within the uppermost 10 cm of the soil profile. Substantial decreases in concentrations of some metal(loid)s were observed with time most likely owing to lower solubility and sorption as a consequence of the increase in pH. In deeper parts of the profiles, porewater remained strongly buffered at low pH values (pH <4.5) and experienced little progression toward anoxic circumneutral pH conditions over the 24 mo of subaqueous conditions. It is proposed that low pH conditions inhibited the activity of SO₄²-reducing bacteria and, in turn, the in situ generation of alkalinity through pyrite production. The limited supply of alkalinity in freshwater systems and the initial highly buffered low pH conditions were also thought to be slowing recovery. The timescales involved for a sulfuric horizon rewetted by a freshwater body to recover from acidic conditions could therefore be in the order of several years.Nathan L. Creeper, Paul Shand, Warren Hicks, and Rob W. Fitzpatric

Behaviour of iron, aluminium and other selected metals following the rewetting of inland acid sulfate soils containing sulfuric material

Also published as: Geological Survey of Finland, 2012; Guide 56:26-28Creeper, N. L., Shand, P., Fitzpatrick, R. W. and Hutson, J.http://projects.gtk.fi/7iassc/conference/programme/presentation.htm

Geochemical processes following freshwater reflooding of acidified inland acid sulfate soils: an in situ mesocosm experiment

Abstract not available.Nathan L. Creeper, Warren S. Hicks, Paul Shand, Rob W. Fitzpatric

Acidity fluxes following rewetting of sulfuric material

We selected two sites with soil materials of clay and sand and used mesocosms to study the effect of rewetting sulfuric material with sea water and fresh water. The materials behaved differently due to different water seepage rates and acid stores. The water seepage rate was low for the clay soil (0.8×10–3 m/d) compared to the sandy soil (8–15×10–3 m/d). Initial acid flux rates were higher (0.1–0.2 mol/m2/d) compared to long term rates (0.007–0.014 mol/m2/d). For the clay soil, the low seepage rate and higher stored acidity resulted in a net flux of solutes from the soil to the water column. In contrast, the higher seepage flux of the sandy material resulted in a flux of water and solutes from the water column into the soil profile, displacing acid pore water deeper into the soil profile. However there is a residual acid flux into the water column probably due to the ongoing and slow dissolution of residual acid oxidation products. In both materials, sea water mobilised more acidity. Comparing the measured flux and calculated advective and diffusive fluxes highlighted the importance of solid phase reactions such as dissolution and surface exchange reactions.W. S. Hicks, N. Creeper, J. Hutson, R. W. Fitzpatrick, S. Grocke and P. Shandhttp://trove.nla.gov.au/work/37679232http://www.iuss.org/19th%20WCSS/19th%20WCSS_Handbook_REAL%20HANDBOOK_V10_BACK%20COVER%20change.pd

Mobilization of acidity and metals during refilling of a dried wetland: A comparison of laboratory and field data

Also published as: Geological Survey of Finland, 2012; Guide 56:110-112Shand, P., Grocke, S., Fitzpatrick R.W., Merry, R.H., Thomas, M. & Creeper N.http://projects.gtk.fi/7iassc/conference/programme/presentation.htm