Numerical simulation of isotope fractionation in steady-state bioreactive transport controlled by transverse mixing

Dominik Eckert, Massimo Rolle, Olaf A. Cirpka

Research output: Contribution to journalJournal articleResearchpeer-review


Compound-specific stable isotope analysis (CSIA) has increasingly been used as a tool to assess intrinsic biodegradation at contaminated field sites. Typically, the Rayleigh equation is used to estimate the extent of biodegradation from measured isotope ratios of the contaminant. However, if the rate-limiting step in overall degradation is not the microbial reaction itself, the Rayleigh equation may no more be applicable. In this study we simulate biodegradation of continuously emitted petroleum hydrocarbons in groundwater systems. These contaminants are effectively degraded at the plume fringe where transverse dispersion makes them mix with dissolved electron acceptors present in the ambient groundwater. We simulate reactive transport to study the coupled effects of transverse mixing and biodegradation on the spatial patterns of carbon isotope signatures and their interpretation based on depth-integrated sampling which represents the most common setup in the assessment of contaminated sites. We present scenarios mimicking a hydraulically uniform laboratory experiment and a field-scale application considering heterogeneous conductivity fields. We compare cases in which isotopologue-specific transverse dispersion is considered to those where this additional fractionation process is neglected. We show that these effects cause significant shifts in the isotopic signals and may lead to overestimation of biodegradation. Moreover, our results provide evidence that the rate-limiting effect of transverse mixing on the overall degradation spatially varies along the length of a steady-state contaminant plume. The control of biodegradation by transverse dispersion and the fractionating effect of dispersion modulate the fractionation caused by the microbial reaction alone. As a consequence, significantly nonlinear isotopic patterns are observed in a Rayleigh plot. Simulations in heterogeneous flow domains show that these effects persist at larger field scales and are sensitive to the degree of mixing enhancement, determined by the heterogeneity of the hydraulic conductivity fields, and to the groundwater flow velocity. © 2012 Elsevier B.V.
Original languageEnglish
JournalJournal of Contaminant Hydrology
Pages (from-to)95-106
Number of pages12
Publication statusPublished - 2012
Externally publishedYes


  • Water Science and Technology
  • Environmental Chemistry
  • Biodegradation
  • Isotope fractionation
  • Mixing
  • Rayleigh equation
  • Transverse dispersion
  • Carbon isotopes
  • Contaminant plume
  • Contaminated sites
  • Coupled effect
  • Degree of mixing
  • Electron acceptor
  • Field scale
  • Fractionation process
  • Groundwater system
  • Heterogeneous flow
  • Intrinsic biodegradation
  • Isotope ratio
  • Isotopic pattern
  • Isotopic signals
  • Laboratory experiments
  • Larger fields
  • Microbial reaction
  • Petroleum hydrocarbons
  • Plume fringes
  • Rate limiting
  • Rate-limiting steps
  • Rayleigh
  • Reactive transport
  • Spatial patterns
  • Stable-isotope analysis
  • Transverse mixing
  • Differential equations
  • Dispersions
  • Groundwater
  • Groundwater flow
  • Groundwater pollution
  • Impurities
  • Isotopes
  • Microbiology
  • Petroleum chemistry
  • carbon
  • ground water
  • hydrocarbon
  • isotope
  • petroleum
  • biodegradation
  • computer simulation
  • fractionation
  • groundwater flow
  • hydraulic conductivity
  • isotopic analysis
  • isotopic fractionation
  • petroleum hydrocarbon
  • Rayleigh number
  • stable isotope
  • article
  • dispersion
  • flow rate
  • isotope analysis
  • plume
  • priority journal
  • simulation
  • steady state
  • Biodegradation, Environmental
  • Environmental Monitoring
  • Models, Theoretical
  • groundwater contaminant biodegradation
  • groundwater flow velocity
  • steady-state contaminant plume
  • Microorganisms (Bacteria, Eubacteria, Microorganisms) - Bacteria [05000] Aromatoleum aromaticum species strain-EbN1
  • carbon isotope
  • electron acceptors
  • petroleum hydrocarbon pollutant, water pollutant
  • 04500, Mathematical biology and statistical methods
  • 10515, Biophysics - Biocybernetics
  • 31000, Physiology and biochemistry of bacteria
  • 37015, Public health - Air, water and soil pollution
  • 39008, Food microbiology - General and miscellaneous
  • Computational Biology
  • compound-specific stable isotope analysis CSIA applied and field techniques
  • depth-integrated sampling applied and field techniques
  • isotope fractionation numerical simulation mathematical and computer techniques
  • Rayleigh equation mathematical and computer techniques
  • Bioprocess Engineering
  • Models and Simulations
  • Pollution Assessment Control and Management


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