Regional Patterns in the Isotopic Composition of Natural and Anthropogenic Nitrate in Groundwater, High Plains, U.S.A.
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- 作者：P. B. McMahon and J. K. Bö ; hlke
- 刊名：Environmental Science & Technology
- 出版年：2006
- 出版时间：May 1, 2006
- 年：2006
- 卷：40
- 期：9
- 页码：2965 - 2970
- 全文大小：180K
- 年卷期：v.40,no.9(May 1, 2006)
- ISSN：1520-5851
文摘
Mobilization of natural nitrate (NO3-) deposits in thesubsoil by irrigation water in arid and semiarid regionshas the potential to produce large groundwater NO3-concentrations. The use of isotopes to distinguish betweennatural and anthropogenic NO3- sources in these settingscould be complicated by the wide range in 
15N valuesof natural NO3-. An ~10 000 year record of paleorechargefrom the regionally extensive High Plains aquifer indicatesthat 15N values for NO3- derived from natural sourcesranged from 1.3 to 12.3” and increased systematically fromthe northern to the southern High Plains. This collectiverange in 15N values spans the range that might be interpretedas evidence for fertilizer and animal-waste sources ofNO3-; however, the 15N values for NO3- in modern recharge(<50 years) under irrigated fields were, for the mostpart, distinctly different from those of paleorecharge whenviewed in the overall regional context. An inverse relationwas observed between the 15N[NO3-] values and theNO3-/Cl- ratios in paleorecharge that is qualitativelyconsistent with fractionating losses of N increasing fromnorth to south in the High Plains. N and O isotope data forNO3- are consistent with both NH3 volatilization anddenitrification, having contributed to fractionating lossesof N prior to recharge. The relative importance of differentisotope fractionating processes may be influenced byregional climate patterns as well as by local variation insoils, vegetation, topography, and moisture conditions.
15N valuesof natural NO3-. An ~10 000 year record of paleorechargefrom the regionally extensive High Plains aquifer indicatesthat 15N values for NO3- derived from natural sourcesranged from 1.3 to 12.3” and increased systematically fromthe northern to the southern High Plains. This collectiverange in 15N values spans the range that might be interpretedas evidence for fertilizer and animal-waste sources ofNO3-; however, the 15N values for NO3- in modern recharge(<50 years) under irrigated fields were, for the mostpart, distinctly different from those of paleorecharge whenviewed in the overall regional context. An inverse relationwas observed between the 15N[NO3-] values and theNO3-/Cl- ratios in paleorecharge that is qualitativelyconsistent with fractionating losses of N increasing fromnorth to south in the High Plains. N and O isotope data forNO3- are consistent with both NH3 volatilization anddenitrification, having contributed to fractionating lossesof N prior to recharge. The relative importance of differentisotope fractionating processes may be influenced byregional climate patterns as well as by local variation insoils, vegetation, topography, and moisture conditions.