esm223_03_Other_Reading_LLNL_Nitrate

esm223_03_Other_Reading_LLNL_Nitrate - This work was...

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Denitrification in a Shallow Aquifer Underlying a Dairy Farm: New Approaches to Characterization and Modeling : UCRL-PRES-207404 Bradley Esser, Harry Beller, Steven F. Carle, G. Bryant Hudson, Staci Kane, Roald Leif, Tracy Letain, Jean E. Moran, Walt W. McNab, and Andrew F.B. Tompson Lawrence Livermore National Laboratory This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48
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We must understand denitrification to simulate nitrate transport ± Heterotrophic denitrification 4NO 3 - + 5CH 2 O + 4H + Æ 2N 2 + 5CO 2 + 7H 2 O ± Autotrophic denitrification 14NO 3 - + 5 FeS 2 + 4H + Æ 7N 2 + 10SO 4 2- + 5Fe 2+ + 2H 2 O ± Denitrification requires Denitrifying bacteria Low oxygen conditions (< 0.6 mg/L) An electron donor N 2 N 2 O Æ NO Æ NO 2 - Æ NO 3 - Æ Nitrogen (0) Nitrous Oxide (+1) Nitric Oxide (+2) Nitrite (+3) Nitrate (+5)
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The Goal is to predict the future concentration of nitrate at a receptor (drinking water well) + + = i NO NO NO NO NO R S x c x x c D t c 3 3 3 3 3 ) ( υ Dispersion : mechanical dispersion, molecular diffusion Advection : bulk groundwater flow Source/sinks : mass loading, reactions Rate of nitrate change at a given receptor = + + Local groundwater velocity: (Darcy’s Law; age gradient) Denitrification rate expression: microbial kinetics Parameters that may vary in space and hence will be modeled stochastically Source loading: nitrate migration to the water table
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Quantifying denitrification requires a multi-disciplinary approach ± Characterization of groundwater flow Historical and current WLs, pump tests Tritium-helium age dating Stable isotopes of the water molecule Vadose zone instrumentation ± Characterization of nitrate biogeochemistry & source Real-time quantitative PCR Microbial kinetics Excess nitrogen Stable isotopes of nitrate ± δ 15 N and δ 18 O of NO 3 Co-contaminants as source tracers ± Modeling groundwater flow and chemistry Stochastic models (for spatial heterogeneity) Streamline & gridded flow & transport models Reactive transport
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We are using a molecular biology approach to measuring denitrification rates in the field Population-normalized denitrification rate ( µ mol nitrate/time/cell,
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This note was uploaded on 08/06/2008 for the course ESM 235 taught by Professor Dunne during the Winter '08 term at UCSB.

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esm223_03_Other_Reading_LLNL_Nitrate - This work was...

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