Fluxes of redox equivalents in metabolic networks at active zones in aquifers
FOR 580 RIC
From 02/2006Principal Investigator: Hans H. Richnow, Matthias Kästner
Grant: FOR 580 Electron Transfer Processes in Anoxic Aquifers
In the first phase of the joint research unit, we provide evidence that the spatial and temporal distribution of methane and sulphur compounds mediated electron transfer reactions over distance in contaminated aquifers. This implies the linkage of carbon and sulphur cycles in aquifers with respect to electron flow mediated by chemolithoautotrophic communities. Reduced products from electron transfer reactions, such as S2- , and CH4 supported chemolithoautotrophic and heterotrophic microbial processes as electron donors, thus linking the nitrogen, iron, sulphur and carbon cycles in aquifers. In addition, we provided evidence for anaerobic methane oxidation in anoxic aquifers. Therefore, the question arises to which terminal electron acceptor the anaerobic methane oxidation in aquifer systems is involved. In the second phase we thus propose to elucidate activity, functionality and composition of methane oxidising microbial communities in aquifers potenially using sulphate, Fe(III) or nitrate a electron acceptor. If anaerobic methane oxidation actually occurs in the aquifer, we can also expect anaerobic sulfide oxidation and we thus propose also to study the sulphur cycle at a laboratory and field scale with respect to sulphur disproportionation reaction and anaerobic oxidation of sulphides in order to elucidate activity, functionality and composition of microbial communities.
To fill this severe gap of knowledge, electron donor - acceptor interactions of microbial systems related to the in situ degradation of contaminants will be studied in aquifers at field and micro scale in order to understand electron transfer processes related to methane and reduced sulphur species. Once formed during contaminant degradation within the plume, methane, ammonia or reduced sulphur species will be transported with the ground water flow and leave the zone of formation. Such compounds become potent electron donors in other geochemical zones of the aquifer and will there become oxidized by microbial processes. Cascades of related redox reactions will follow consuming electron acceptors reduced in previous processes that now become available as electron donors for other processes at geochemical gradients. The transport of methane, ammonia and reduced sulphur species is linking microbial metabolic networks over certain distances in contaminated aquifers and is the important element in the regulation of carbon and electron flux in contaminated aquifers. Related to methane and reduced sulphur compounds, this flux will be analysed in zones microbially active in contaminant degradation. Furthermore, the microbial processes, their contribution to the overall redox processes, and the spatial and temporal variation will be described by an integrated study that traces the turnover based on the signature of stable isotopes and labelled compounds.