Decomposition and alteration of organic matter during remediation of a sandy acid sulfate soil

Dr Angelika Koelbl1,2, Franziska Bucka1, Prof Petra Marschner3, Prof Luke Mosley4, Prof Rob Fitzpatrick4, Prof Ingrid Koegel-Knabner1,5

1Soil science, Technical University of Munich, Freising, Germany, 2Soil science, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany, 3School of Agriculture, Food and Wine, The University of Adelaide, Adelaide, Australia, 4Acid Sulfate Soils Centre, The University of Adelaide, Adelaide, Australia, 5Institute for Advanced Study, Technical University of Munich, Garching, Germany

When acid sulfate soils dry, oxidation of pyrite can cause strong acidification (pH <4) to form sulfuric material. Re-saturation of acid sulfate soils with sulfuric material can lead to re-formation of Fe-sulfides and pH increase through activity of sulfate reducing bacteria (SRB), which require sufficient available organic carbon (OC). Despite the general knowledge about positive impacts of OC sources for ameliorating sulfuric soils, little is known about OC consumption and changes of OC composition of native and added organic substrates during the amelioration process. To investigate remediation of a sandy, OC-poor sulfuric soil (initial pH = 2.5), a 10-week anoxic incubation experiment was conducted under submerged conditions. Organic C amounts between 50% up to 200% of the native soil OC content were added as wheat straw and lactate. Lactate was used to test if this selectively promotes the activity of SRB, and thus, accelerates sulfate reduction and pH neutralization. The results showed that OC additions of ≥ 50% of native soil OC content and pre-adjustment of pH to values ≥ 5.0 were sufficient to enhance microbial reduction, which increased the pH to values ≥ 5.5. Further, OC additions of ≥ 100% of native soil OC increased mineral-associated OC. The addition of OC as lactate solution in combination with wheat straw led to quickest changes of pH and redox values and resulted in pH ≥ 7 and redox values ≤ -300mV, which was accompanied by high CO₂ release indicating an active microbial population. Thus, application of wheat straw-lactate – mixtures led to the quickest remediation success. However, OC losses due to microbial degradation and formation of less available mineral-associated OC may require repeated OC addition.


Between 2000 and 2018, Angelika Kölbl was postdoctoral researcher at the Chair of Soil Science, Technical University of Munich, Germany. In 2019, she started to work at the Institute of Soil Science, Martin Luther University Halle-Wittenberg, Germany. Her research focuses on the amount, composition and allocation of soil organic matter under different land uses, with particular regard to changing redox conditions. In her current research project, she investigates the composition, storage and availability of organic matter in acid sulfate soils.

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