title: Estimating pathway-specific contributions to biodegradation in aquifers based on dual isotope analysis: theoretical analysis and reactive transport simulations.
abstract: At field sites with varying redox conditions, different redox-specific microbial degradation pathways contribute to total contaminant degradation. The identification of pathway-specific contributions to total contaminant removal is of high practical relevance, yet difficult to achieve with current methods. Current stable-isotope-fractionation-based techniques focus on the identification of dominant biodegradation pathways under constant environmental conditions. We present an approach based on dual stable isotope data to estimate the individual contributions of two redox-specific pathways. We apply this approach to carbon and hydrogen isotope data obtained from reactive transport simulations of an organic contaminant plume in a two-dimensional aquifer cross section to test the applicability of the method. To take aspects typically encountered at field sites into account, additional simulations addressed the effects of transverse mixing, diffusion-induced stable-isotope fractionation, heterogeneities in the flow field, and mixing in sampling wells on isotope-based estimates for aerobic and anaerobic pathway contributions to total contaminant biodegradation. Results confirm the general applicability of the presented estimation method which is most accurate along the plume core and less accurate towards the fringe where flow paths receive contaminant mass and associated isotope signatures from the core by transverse dispersion. The presented method complements the stable-isotope-fractionation-based analysis toolbox. At field sites with varying redox conditions, it provides a means to identify the relative importance of individual, redox-specific degradation pathways.
authors.affiliation: UFZ-Helmholtz Centre for Environmental Research, Department of Environmental Microbiology, Permoserstraße 15, D-04318 Leipzig, Germany. florian.centler@ufz.de
authors.forename: Florian
authors.initials: F
authors.lastname: Centler
authors.forename: Falk
authors.initials: F
authors.lastname: Heße
authors.forename: Martin
authors.initials: M
authors.lastname: Thullner
mesh_terms: D001673:Biodegradation, Environmental; D004784:Environmental Monitoring / Q000379:methods*; D060587:Groundwater; D007554:Isotopes / Q000032:analysis*; D014874:Water Pollutants, Chemical
chemical_list: D007554:Isotopes; D014874:Water Pollutants, Chemical
keywords: Biodegradation; Dual stable isotope analysis; Reactive transport modeling; Redox zonation; Stable isotope fractionation; Transverse mixing