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Regional patterns in the isotopic composition of natural and anthropogenic nitrate in groundwater, High Plains, U.S.A.

Environmental Science and Technology

By:
and
DOI: 10.1021/es052229q

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Abstract

Mobilization of natural nitrate (NO3-) deposits in the subsoil by irrigation water in arid and semiarid regions has the potential to produce large groundwater NO3- concentrations. The use of isotopes to distinguish between natural and anthropogenic NO3- sources in these settings could be complicated by the wide range in ??15N values of natural NO3-. An ???10 000 year record of paleorecharge from the regionally extensive High Plains aquifer indicates that ??15N values for NO3- derived from natural sources ranged from 1.3 to 12.3% and increased systematically from the northern to the southern High Plains. This collective range in ??15N values spans the range that might be interpreted as evidence for fertilizer and animal-waste sources of NO3-; however, the ??15N values for NO3- in modern recharge (<50 years) under irrigated fields were, for the most part, distinctly different from those of paleorecharge when viewed in the overall regional context. An inverse relation was observed between the ??15N[NO3-] values and the NO 3-/CI- ratios in paleorecharge that is qualitatively consistent with fractionating losses of N increasing from north to south in the High Plains. N and O isotope data for NO3- are consistent with both NH3 volatilization and denitrification, having contributed to fractionating losses of N prior to recharge. The relative importance of different isotope fractionating processes may be influenced by regional climate patterns as well as by local variation in soils, vegetation, topography, and moisture conditions.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Regional patterns in the isotopic composition of natural and anthropogenic nitrate in groundwater, High Plains, U.S.A.
Series title:
Environmental Science and Technology
DOI:
10.1021/es052229q
Volume
40
Issue:
9
Year Published:
2006
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Environmental Science and Technology
First page:
2965
Last page:
2970
Number of Pages:
6