Redox processes involving humic substances
FOR 580 KAP
From 02/2006Principal Investigator: Andreas Kappler
Grant: FOR 580 Electron Transfer Processes in Anoxic Aquifers
Humified natural organic matter (humic substances) is present in most aquatic and terrestrial environments; it is redox-active, can be reduced chemically and microbially and interacts with organic and inorganic contaminants by adsorption, complexation and redox reactions. In the first funding period of this research project we demonstrated that humic substances can function as electron shuttles in anoxic aquifers. However, the specific conditions under which this shuttling can happen and the molecular processes involved in humic substance electron shuttling are still unknown. In this follow-up project we therefore intend to identify whether humic substances can function as electron shuttle between microbes and solid-phase electron acceptors under conditions as they could be present in anoxic aquifers with regard to the concentrations of humic substances, presence of silica and other ions (e.g. phosphate), different ratios of iron minerals to microbial cells, spatial distances between cells and iron minerals as well as identity and quantity of iron minerals. This interdisciplinary research project combines microbiological, geochemical, mineralogical, spectroscopical and modeling studies to better understand the role of humic substances in microbial and chemical redox processes in anoxic environments.
In this project, we focus on the role of humic substances in microbial and chemical electron transfer processes in anoxic aquifers. We hypothesize that humic substances can function as electron acceptor in microbial redox processes in anoxic aquifers and, because humic substances are able to transfer the accepted electrons further to insoluble electron acceptors such as Fe(III)-minerals, represent therefore a main pathway for the electron flow in such environments. Redox properties of different humic substances and different humic substance fractions will be determined and redox reactions of humic substances with microorganisms and iron minerals will be quantified. The consequences of humic substance reduction for its reactivity will be determined with arsenic as an example for a toxic, redox-active metal ion whose complexation and redox transformation by humic substances will be quantified.
This interdisciplinary research project combines microbiological and geochemical studies to better understand the role of humic substances in microbial and chemical redox processes in anoxic environments.