title: Monitoring and assessment of surface water acidification following rewetting of oxidised acid sulfate soils.
abstract: Large-scale exposure of acid sulfate soils during a hydrological drought in the Lower Lakes of South Australia resulted in acidification of surface water in several locations. Our aim was to describe the techniques used to monitor, assess and manage these acidification events using a field and laboratory dataset (n = 1,208) of acidic to circum-neutral pH water samples. The median pH of the acidified (pH < 6.5) samples was 3.8. Significant (p < 0.05) increases in soluble metals (Al, Co, Mn, Ni and Zn above guidelines for ecosystem protection), SO4 (from pyrite oxidation), Si (from aluminosilicate dissolution) and Ca (from carbonate dissolution and limestone addition), were observed under the acidic conditions. The log of the soluble metal concentrations, acidity and SO4/Cl ratio increased linearly with pH. The pH, alkalinity and acidity measurements were used to inform aerial limestone dosing events to neutralise acidic water. Field measurements correlated strongly with laboratory measurements for pH, alkalinity and conductivity (r (2) ≥ 0.97) but only moderately with acidity (r (2) = 0.54), which could be due to difficulties in determining the indicator-based field titration endpoint. Laboratory measured acidity correlated well with calculated acidity (r (2) = 0.87, acidity present as Al(III) >> H(+) ≈ Mn(II) > Fe(II/III)) but was about 20 % higher on average. Geochemical speciation calculations and XRD measurements indicated that solid phase minerals (schwertmannite and jarosite for Fe and jurbanite for Al) were likely controlling dissolved metal concentrations and influencing measured acidity between pH 2 and 5.
authors.affiliation: Water Quality Branch, Environment Protection Authority (South Australia), GPO Box 2607, Adelaide, SA, 5001, Australia, luke.mosley@epa.sa.gov.au.
authors.forename: Luke M
authors.initials: LM
authors.lastname: Mosley
authors.forename: Benjamin
authors.initials: B
authors.lastname: Zammit
authors.forename: Ann-Marie
authors.initials: AM
authors.lastname: Jolley
authors.forename: Liz
authors.initials: L
authors.lastname: Barnett
authors.forename: Rob
authors.initials: R
authors.lastname: Fitzpatrick
mesh_terms: D004784:Environmental Monitoring; D005618:Fresh Water; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D012987:Soil / Q000737:chemistry*; D013021:South Australia; D013431:Sulfates / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D012987:Soil; D013431:Sulfates; D014874:Water Pollutants, Chemical
references.citation: Environ Sci Technol. 2002 Jul 15;36(14):3096-103
references.pmid: 12141489
references.citation: Environ Sci Technol. 2003 Mar 1;37(5):958-71
references.pmid: 12666927
references.citation: Environ Sci Technol. 2003 Aug 1;37(15):3303-8
references.pmid: 12966974