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Complexities of aquifer systems impede reaction rate estimates

Date:
August 31, 2010
Source:
American Geophysical Union
Summary:
Contaminant concentrations in aquifers can change as chemical reactions occur during groundwater transport through the aquifer. For instance, denitrification, in which the contaminant nitrate is converted to molecular nitrogen, reduces nitratecontaminant loads. It is useful to understand the rates at which denitrification and other reactions occur in an aquifer to improve understanding and prediction of contaminant migration.

Contaminant concentrations in aquifers can change as chemical reactions occur during groundwater transport through the aquifer. For instance, denitrification, in which the contaminant nitrate is converted to molecular nitrogen, reduces nitratecontaminant loads. It is useful to understand the rates at which denitrification and other reactions occur in an aquifer to improve understanding and prediction of contaminant migration.

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However, estimates of denitrification and other reaction rates are often based on simplified transport models, typically by assuming all water in a sample has the same travel time and reaction history, an unrealistic assumption in many cases because of mixing of water in complex, geologically heterogeneous natural systems. To investigate the effects of mixing during transport in a heterogeneous environment on reaction rate estimates, Green et al. study an aquifer in the San Joaquin Valley using field observations and numerical models.

They find that apparent isotope fractionation and reaction rate estimates derived from field data using simple models are quite different from intrinsic (true) values from more realistic models accounting for heterogeneity. In fact, the apparent and true rates can differ by an order of magnitude or more. Moreover, the true parameter values for isotope fractionation and oxygen inhibition are in much better agreement with laboratory data than field-based estimates that do not account for mixing. They conclude that the effects of mixing during transport through a heterogeneous aquifer are important and that models accounting for these effects can improve forecasts of reaction progress.

Authors of the study include: Christopher T. Green, Barbara A. Bekins: U.S. Geological Survey, Menlo Park, CA, USA John Karl Böhlke: U.S. Geological Survey, Reston, VA, USA Steven P. Phillips: U.S. Geological Survey, Sacramento, CA, USA.


Story Source:

The above story is based on materials provided by American Geophysical Union. Note: Materials may be edited for content and length.


Journal Reference:

  1. Christopher T. Green, John Karl Böhlke, Barbara A. Bekins, Steven P. Phillips. Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer. Water Resources Research, 2010; 46 (8): W08525 DOI: 10.1029/2009WR008903

Cite This Page:

American Geophysical Union. "Complexities of aquifer systems impede reaction rate estimates." ScienceDaily. ScienceDaily, 31 August 2010. <www.sciencedaily.com/releases/2010/08/100831095450.htm>.
American Geophysical Union. (2010, August 31). Complexities of aquifer systems impede reaction rate estimates. ScienceDaily. Retrieved March 27, 2015 from www.sciencedaily.com/releases/2010/08/100831095450.htm
American Geophysical Union. "Complexities of aquifer systems impede reaction rate estimates." ScienceDaily. www.sciencedaily.com/releases/2010/08/100831095450.htm (accessed March 27, 2015).

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