Does iron cycling trigger generation of acidity in groundwaters of Western Australia?

In large areas of Western Australia, acidic groundwaters occur with pH values distinctly lower than 3, generation of which has been attributed to the oxidation of Fe(II). Incubation experiments performed with sediments from playas receiving acid groundwater demonstrated occurrence of reductive dissolution of ferric iron minerals at rates [670 nmol (g reactive iron)(-1) h(-1)] similar to those observed in sediments of acidic mining lakes (AML), indicating thatthe pH was established through an acidity-driven iron cycle in analogy to processes occurring in AML systems. The low pH values observed in acidic groundwaters and AML, however, can only be achieved if the anion corresponding to Fe(III) is that of a strong acid. In AML, sulfate is derived from pyrite oxidation. Because this process is reported not to occur in the acidic groundwater systems of Western Australia, we have derived a conceptual model according to which sulfate is generated upon reaction of weathering-derived alkalinity with gypsum to form calcite, which is abundant in these areas. The model proposes that part of the alkalinity generated during weathering is stared as calcite in the landscape, which leads to spatial separation of acidity and alkalinity.