The influence of schwertmannite on acidification and sulfide formation in acid sulfate soil landscapes

Document Type

Conference publication

Publication details

Henderson, SP, Sullivan, LA, Bush, RT & Burton, ED 2006, 'The influence of schwertmannite on acidification and sulfide formation in acid sulfate soil landscapes', Abstracts and programme: Soil science solving problems : ASSSI-ASPAC-ACMS National Soils Conference, Adelaide, SA, 3-7 December, Australian Society of Soil Science Inc., the Australasian Soil and Plant Analysis Council, in association with the Australian Clay Minerals Society.


In coastal lowland acid sulfate soil (CLASS) landscapes, the iron hydroxy-sulfate mineral schwertmannite (Fe8 O8(OH)5.5(SO4)1.25) forms as pedofeatures such as macropore coatings and as ground surface layers. A series of experiments were conducted to examine the geochemical behavior of these pedofeatures under aerobic and anaerobic conditions. Samples of schwertmannite-rich pedofeatures were suspended in water over 10 days to examine their acidification behaviour. An anaerobic incubation was undertaken over 203 days to examine the influence of these pedofeatures on water quality and the reduction of sulfate and formation of sulfide. The results clearly show that the schwertmannite-rich pedofeatures, when introduced to water under aerobic conditions, rapidly release readily available acidity (>70mol H2SO-t 4 ) whilst retaining significantly greater amounts of titratable actual acidity (>970mol H2SO-t 4 ). This study provides the first evidence that schwertmannite-rich pedofeatures store acidity in multiple phases of differing availability and describes the behaviour of these phases. Under anaerobic conditions, Schwertmannite-rich pedofeatures enhance the formation of reduced inorganic sulfur species, (aqueous sulfide, iron monosulfide, pyrite and elemental sulfur). The data indicate that schwertmannite-rich pedofeatures act as a reservoir supplying reactants for sulfide formation which thereby promotes an increased production of reduced inorganic sulfur species. The presence of schwertmannite and its effect on contemporary iron, sulfur and acidity cycling has implications for CLASS land management and water quality