Arid
DOI10.1111/gwat.12463
Density-Driven Free-Convection Model for Isotopically Fractionated Geogenic Nitrate in Sabkha Brine
Wood, Warren W.1; Bohlke, J. K.2
通讯作者Wood, Warren W.
来源期刊GROUNDWATER
ISSN0017-467X
EISSN1745-6584
出版年2017
卷号55期号:2页码:199-207
英文摘要

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 similar to 525 mg/L (as N), NO3- in the coastal sabkhas of Abu Dhabi is enriched in N-15 (mean delta N-15 similar to 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 Delta O-17, delta N-15, and delta O-18 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 (N-2), 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-.


类型Article
语种英语
国家USA
收录类别SCI-E
WOS记录号WOS:000395640200008
WOS关键词ISOTOPE FRACTIONATION ; UNITED-STATES ; GROUND-WATER ; ABU-DHABI ; OXYGEN ; NITROGEN ; DESERT ; PERCHLORATE ; TRANSPORT
WOS类目Geosciences, Multidisciplinary ; Water Resources
WOS研究方向Geology ; Water Resources
来源机构United States Geological Survey
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/199396
作者单位1.Michigan State Univ, Dept Geol Sci, 288 Farm Lane, E Lansing, MI 48824 USA;
2.US Geol Survey, 431 Natl Ctr, Reston, VA 20192 USA
推荐引用方式
GB/T 7714
Wood, Warren W.,Bohlke, J. K.. Density-Driven Free-Convection Model for Isotopically Fractionated Geogenic Nitrate in Sabkha Brine[J]. United States Geological Survey,2017,55(2):199-207.
APA Wood, Warren W.,&Bohlke, J. K..(2017).Density-Driven Free-Convection Model for Isotopically Fractionated Geogenic Nitrate in Sabkha Brine.GROUNDWATER,55(2),199-207.
MLA Wood, Warren W.,et al."Density-Driven Free-Convection Model for Isotopically Fractionated Geogenic Nitrate in Sabkha Brine".GROUNDWATER 55.2(2017):199-207.
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