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231224s2017 xx |||||o 00| ||eng c |
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|a 10.1111/gwat.12463
|2 doi
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|a pubmed24n0888.xml
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|a (NLM)27893932
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|a DE-627
|b ger
|c DE-627
|e rakwb
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|a eng
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| 100 |
1 |
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|a Wood, Warren W
|e verfasserin
|4 aut
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| 245 |
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|a Density-Driven Free-Convection Model for Isotopically Fractionated Geogenic Nitrate in Sabkha Brine
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|c 2017
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| 336 |
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|a Text
|b txt
|2 rdacontent
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|a ƒaComputermedien
|b c
|2 rdamedia
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|a ƒa Online-Ressource
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|2 rdacarrier
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|a Date Completed 08.12.2017
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|a Date Revised 02.12.2018
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|a published: Print-Electronic
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|a Citation Status MEDLINE
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|a © 2016, National Ground Water Association.
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|a Subsurface brines with high nitrate (NO3- ) concentration are common in desert environments as atmospheric nitrogen is concentrated by the evaporation of precipitation and little nitrogen uptake. However, in addition to having an elevated mean concentration of ∼525 mg/L (as N), NO3- in the coastal sabkhas of Abu Dhabi is enriched in 15 N (mean δ15 N ∼17‰), which is an enigma. A NO3- solute mass balance analysis of the sabkha aquifer system suggests that more than 90% of the nitrogen is from local atmospheric deposition and the remainder from ascending brine. In contrast, isotopic mass balances based on Δ17 O, δ15 N, and δ18 O data suggest approximately 80 to 90% of the NO3- could be from ascending brine. As the sabkha has essentially no soil, no vegetation, and no anthropogenic land or water use, we propose to resolve this apparent contradiction with a density-driven free-convection transport model. In this conceptual model, the density of rain is increased by solution of surface salts, transporting near-surface oxygenated NO3- bearing water downward where it encounters reducing conditions and mixes with oxygen-free ascending geologic brines. In this environment, NO3- is partially reduced to nitrogen gas (N2 ), thus enriching the remaining NO3- in heavy isotopes. The isotopically fractionated NO3- and nitrogen gas return to the near-surface oxidizing environment on the upward displacement leg of the free-convection cycle, where the nitrogen gas is released to the atmosphere and new NO3- is added to the system from atmospheric deposition. This recharge/recycling process has operated over many cycles in the 8000-year history of the shallow aquifer, progressively concentrating and isotopically fractionating the NO3-
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|a Journal Article
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|a Nitrates
|2 NLM
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|a Nitrogen Isotopes
|2 NLM
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7 |
|a Salts
|2 NLM
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| 650 |
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|a Water Pollutants, Chemical
|2 NLM
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| 650 |
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7 |
|a brine
|2 NLM
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| 650 |
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|a Nitrogen
|2 NLM
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| 650 |
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|a N762921K75
|2 NLM
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| 700 |
1 |
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|a Böhlke, J K
|e verfasserin
|4 aut
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|i Enthalten in
|t Ground water
|d 1979
|g 55(2017), 2 vom: 15. März, Seite 199-207
|w (DE-627)NLM098182528
|x 1745-6584
|7 nnns
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| 773 |
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|g volume:55
|g year:2017
|g number:2
|g day:15
|g month:03
|g pages:199-207
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|u http://dx.doi.org/10.1111/gwat.12463
|3 Volltext
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