Perchlorate in Pleistocene and Holocene Groundwater in North-Central New Mexico
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- 作者：L. Niel Plummer ; John Karl Bö ; hlke ; and Michael W. Doughten
- 刊名：Environmental Science & Technology
- 出版年：2006
- 出版时间：March 15, 2006
- 年：2006
- 卷：40
- 期：6
- 页码：1757 - 1763
- 全文大小：409K
- 年卷期：v.40,no.6(March 15, 2006)
- ISSN：1520-5851
文摘
Groundwater from remote parts of the Middle Rio GrandeBasin in north-central New Mexico has perchlorate(ClO4-) concentrations of 0.12-1.8 
g/L. Because thewater samples are mostly preanthropogenic in age (0-28 000 years) and there are no industrial sources in the studyarea, a natural source of the ClO4- is likely. Most of thesamples have Br-, Cl-, and SO42- concentrations that aresimilar to those of modern bulk atmospheric depositionwith evapotranspiration (ET) factors of about 7-40. Mostof the ET values for Pleistocene recharge were nearly twicethat for Holocene recharge. The NO3-/Cl- and ClO4-/Cl-ratios are more variable than those of Br-/Cl- or SO42-/Cl-. Samples thought to have recharged under the mostarid conditions in the Holocene have relatively high NO3-/Cl- ratios and low 
15N values (+1 per mil (”)) similarto those of modern bulk atmospheric N deposition. The 18Ovalues of the NO3- (-4 to 0 ”) indicate that atmosphericNO3- was not transmitted directly to the groundwaterbut may have been cycled in the soils before infiltrating.Samples with nearly atmospheric NO3-/Cl- ratios haverelatively high ClO4- concentrations (1.0-1.8 g/L) with anearly constant ClO4-/Cl- mole ratio of (1.4 ± 0.1) ×10-4, which would be consistent with an average ClO4-concentration of 0.093 ± 0.005 g/L in bulk atmosphericdeposition during the late Holocene in north-central NM.Samples thought to have recharged under wetter conditionshave higher 15N values (+3 to +8 ”), lower NO3-/Cl-ratios, and lower ClO4-/Cl- ratios than the ones most likelyto preserve an atmospheric signal. Processes in thesoils that may have depleted atmospherically derived NO3-also may have depleted ClO4- to varying degrees priorto recharge. If these interpretations are correct, then ClO4-concentrations of atmospheric origin as high as 4 g/Lare possible in preanthropogenic groundwater in parts ofthe Southwest where ET approaches a factor of 40.Higher ClO4- concentrations in uncontaminated groundwatercould occur in recharge beneath arid areas where ET isgreater than 40, where long-term accumulations ofatmospheric salts are leached suddenly from dry soils, orwhere other (nonatmospheric) natural sources of ClO4-exist.
g/L. Because thewater samples are mostly preanthropogenic in age (0-28 000 years) and there are no industrial sources in the studyarea, a natural source of the ClO4- is likely. Most of thesamples have Br-, Cl-, and SO42- concentrations that aresimilar to those of modern bulk atmospheric depositionwith evapotranspiration (ET) factors of about 7-40. Mostof the ET values for Pleistocene recharge were nearly twicethat for Holocene recharge. The NO3-/Cl- and ClO4-/Cl-ratios are more variable than those of Br-/Cl- or SO42-/Cl-. Samples thought to have recharged under the mostarid conditions in the Holocene have relatively high NO3-/Cl- ratios and low 15N values (+1 per mil (”)) similarto those of modern bulk atmospheric N deposition. The 18Ovalues of the NO3- (-4 to 0 ”) indicate that atmosphericNO3- was not transmitted directly to the groundwaterbut may have been cycled in the soils before infiltrating.Samples with nearly atmospheric NO3-/Cl- ratios haverelatively high ClO4- concentrations (1.0-1.8 g/L) with anearly constant ClO4-/Cl- mole ratio of (1.4 ± 0.1) ×10-4, which would be consistent with an average ClO4-concentration of 0.093 ± 0.005 g/L in bulk atmosphericdeposition during the late Holocene in north-central NM.Samples thought to have recharged under wetter conditionshave higher 15N values (+3 to +8 ”), lower NO3-/Cl-ratios, and lower ClO4-/Cl- ratios than the ones most likelyto preserve an atmospheric signal. Processes in thesoils that may have depleted atmospherically derived NO3-also may have depleted ClO4- to varying degrees priorto recharge. If these interpretations are correct, then ClO4-concentrations of atmospheric origin as high as 4 g/Lare possible in preanthropogenic groundwater in parts ofthe Southwest where ET approaches a factor of 40.Higher ClO4- concentrations in uncontaminated groundwatercould occur in recharge beneath arid areas where ET isgreater than 40, where long-term accumulations ofatmospheric salts are leached suddenly from dry soils, orwhere other (nonatmospheric) natural sources of ClO4-exist.