The contribution of low-molecular weight acids (LMWA) and dissolved organic sulfur compounds (DOSC) to the effects of dissolved organic matter (DOM) on redox processes


From 02/2006

Principal Investigator: Christian Zwiener
Staff: Carsten Jobelius
Grant: FOR 580 Electron Transfer Processes in Anoxic Aquifers

In anoxic aquifers organic matter can be degraded biochemically under reduction of sulfate and ferric iron. The occurrence of aromatic and heterocyclic low-molecular weight acids (LMWA) has been attributed to metabolic and co-metabolic degradation pathways in anoxic aquifers. LMWA can make up a considerable portion of dissolved organic matter (DOM) in zones of high substrate concentrations and high biodegradation activity and therefore affect the biotic and abiotic reactivity of iron species in crystalline, colloidal or dissolved form. Furthermore it is expected that in sulfide rich environments as they occur under sulfate reducing conditions sulfur will be incorporated into dissolved organic matter (DOM) and thus produce dissolved organic sulfur compounds (DOSC) which considerably affect the properties of DOM concerning complexation, interaction with surfaces and redox reactions. In the proposed project we intend to identify the contribution of low-molecular weight acids (LMWA) and dissolved organic sulfur compounds (DOSC) to dissolved organic matter (DOM) in anoxic aquifers by analysis of field samples and by laboratory studies on sulfur incorporation into DOM. Furthermore, the effect of LMWA and DOSC to the effects of DOM on iron-based redox processes and colloid formation and reactivity will be investigated by electrochemical and spectroscopic analysis techniques in laboratory experiments. Arylsuccinate derivatives have emerged as potentially universal metabolic biomarkers for the transformation of toluene, xylene, ethylbenzene, and methylnaphthalene under anaerobic conditions. They were identified in laboratory cultures and partly in field samples. Their occurrence and distribution in the field has been neither investigated yet systematically, nor were the geochemical and hydraulic parameters investigated that may influence formation and further turnover of metabolites.

Therefore, we will use in this project succinic acid derivatives and other acidic aromatic or aliphatic metabolites to monitor and understand the transformation of organic compounds by electron transfer processes. Data of the occurrence and spatial distribution of metabolites will be further used to elucidate their role as electron donors and to estimate the relevance of the electron donor function.

For that purpose we will use column experiments with pure cultures to investigate the formation and turnover of specific metabolites (e.g. arylsuccinates, arylcarboxylic acids, low-molecular weight acids) and influencing parameters. The data obtained from those experiments will be used for reactive transport modeling. The calibrated model will then be used to simulate metabolite occurrence and distribution in different scenarios.

Bioreactor experiments will address the question on contaminant degradation and metabolite formation/turnover with an inoculum of non-contaminated peat land under different geochemical conditions (boundary conditions). Metabolite accumulation will be of particular interest in this context. Field measurements will be performed in geochemically reactive zones of the site, where we will investigate metabolite pattern, their spatial distribution and accumulation.

Analytical methods mainly with liquid chromatography-tandem mass spectrometry (LC-MS-MS) combined with different derivatization reactions will be developed to guarantee successful metabolite analysis in small sample volumes of column experiments and in groundwater samples of field sites.

last modified 2009-06-08