1 / 15

Oxidation-Reduction Processes in Ground-Water Systems

Oxidation-Reduction Processes in Ground-Water Systems. Chapelle Groundwater Microbiology and Geochemistry Chapter. REDOX. If Dr. Alpers has taught me anything, its. REDOX. If Dr. Alpers has taught me anything, its. 3+. 2+. Non Equilibrium of Groundwater Various Redox Couples

royal
Télécharger la présentation

Oxidation-Reduction Processes in Ground-Water Systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Oxidation-Reduction Processes in Ground-Water Systems Chapelle Groundwater Microbiology and Geochemistry Chapter

  2. REDOX • If Dr. Alpers has taught me anything, its...

  3. REDOX • If Dr. Alpers has taught me anything, its... 3+ 2+

  4. Non Equilibrium of Groundwater • Various Redox Couples • 2 ways to figure out Redox • Nerst Equation • Thermodynamic Problem: including a known free ENERGY • Kinetic Approach • Measure electrical potential: another form of ENERGY transfer e creates energy -> elec. current generated =amperage - Fig 10.4 The lack of internal consistency between Ehs calculated with different redox couples as observed by Lindberg and Runnels (1984)

  5. Microbial Influence • Microorganisms • use electron transfer to maintain life functions • respiration, activity, and growth create electro kinetic conditions

  6. Describing Kinetic Redox Processes • Include three components: • document source of e that supports microbial metabolism • documentsink for the e that supports microbial metabolism • document rates of e transfer • Microbes are the catalyst for most reactions - - - Why this difference with microbes present ?

  7. Identifying Electron Donors • An Example: • Long, Long ago scientist were confused. • Ocean had low magnesium and nodules with high concentrations of other metals • Submarine Alvin found gushing hot springs at spreading centers • Water rich in Fe, Mn, H2S mixes with O2 rich Sea Water • Ground Water Carbon is abundant • but it is important to figure out the species • DCE-common contaminant can be Electron Donor Sink (acceptor) Source (donor)

  8. Identifying Electron Acceptors • Acceptors in Microbial Metabolism • Oxygen, Nitrate, Mn(IV), Fe(III), Sulfate, CO2 • BUT Carbon is the most abundant • Microbial Ecology and Competition • H2 is most widely used for anaerobic respiration • Steady State Conditions will follow this order • Methanogens > Sulfate reducers > Fe(III) reducers > Nitrate reducers Michaelis-Menton Kinetics

  9. Free Energy from Hydrogen Oxidation Processes • Dictates the Steady State Concentration • High Hydrogen Concentration • Low Hydrogen Concentration • Methanogenic • Sulfate-reducing • Fe(III)-reducing • Mn(IV)-reducing • Nitrate-reducing

  10. Hydrogen concentration develop due to differeing uptake efficiencies Organic Matter initially consumed by fermenting bacteria producing H Depending on which donors are available, H concentrations will differ

  11. Ambient TEAPs (terminal electron-accepting process) • Net Effect- segregate aquifers into discreet zones dominated by electron accepting processes. donor rich in contaminated aquifer donor poor in pristine aquifer Deplete the most efficient electron donor first-> reversed TEAPS Dominated by aerobic, then when O2 used up ->moves to TEAPS Lets think about this in terms of hyporheic zone

  12. Can this work in the Hyporheic Zone? Presence of particular electron acceptor = redox zone Oxygen decrease at depth-active O2 reduction O2 depleted Nitrate falls- nitrate reduction Completely anoxic Mn2+ accumulates- Mn(IV) reduction Nitrate is completely consumed- Fe 2+ accumulates Hyporheic Zone and Riparian Zone more complicated because flowing water Indicates reduction is occurring somewhere up gradient.

  13. Must be Sherlocky and use simple deducing • Use data in conjunction • Doners present • Acceptors present • H concentrations

  14. Hyporhiec Zone Redox USGS, 2013 Riparian Zone Redox Cygan, 2007; Vadose Zone Journal

  15. Questions

More Related