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Perchlorate in Pleistocene and Holocene groundwater in North-Central New Mexico

机译：新墨西哥州中北部更新世和全新世地下水中的高氯酸盐

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Groundwater from remote parts of the Middle Rio Grande Basin in north-central New Mexico has perchlorate (CO4-) concentrations of 0.12-1.8 mu g/L. Because the water samples are mostly preanthropogenic in age (028 000 years) and there are no industrial sources in the study area, a natural source of the ClO4- is likely. Most of the samples have Br-, Cl-, and SO42- concentrations that are similar to those of modern bulk atmospheric deposition with evapotranspiration (ET) factors of about 7-40. Most of the ET values for Pleistocene recharge were nearly twice that for Holocene recharge. The NO3-/Cl- and ClO4-/Cl- ratios are more variable than those of Br-/Cl- or SO4 (2-)/ Cl-. Samples thought to have recharged under the most arid conditions in the Holocene have relatively high NO3 Cl- ratios and low delta N-15 values (+1 per mil (parts per thousand)) similar to those of modern bulk atmospheric N deposition. The delta O-18 values of the NO3 (-4 to 0 parts per thousand) indicate that atmospheric NO3 was not transmitted directly to the groundwater but may have been cycled in the soils before infiltrating. Samples with nearly atmospheric NO3-/Cl- ratios have relatively high ClO4- concentrations (1.0-1.8 mu g/L) with a nearly constant ClO4-/Cl- mole ratio of (1.4 +/- 0.1) x 10(-4), which would be consistent with an average ClO4- concentration of 0.093 +/- 0.005 mu g/L in bulk atmospheric deposition during the late Holocene in north-central NM. Samples thought to have recharged under wetter conditions have higher (delta N-15 values (+3 to +8 parts per thousand), lower NO3-/Cl- ratios, and lower ClO4-/Cl- ratios than the ones most likely to preserve an atmospheric signal. Processes in the soils that may have depleted atmospherically derived NO3 also may have depleted ClO4- to varying degrees prior to recharge. If these interpretations are correct, then ClO4- concentrations of atmospheric origin as high as 4 mu g/L are possible in preanthropogenic groundwater in parts of the Southwest where ET approaches a factor of 40. Higher ClO4- concentrations in uncontaminated groundwater could occur in recharge beneath arid areas where ET is greater than 40, where long-term accumulations of atmospheric salts are leached suddenly from dry soils, or where other (nonatmospheric) natural sources Of ClO4- exist.
机译：来自新墨西哥州中北部大里奥格兰德盆地中部偏远地区的地下水中高氯酸盐（CO4-）的浓度为0.12-1.8μg / L。由于水样的年龄大多是人类活动前的（028 000年），并且研究区域内没有任何工业来源，因此ClO4-的自然来源很可能。大多数样品的Br-，Cl-和SO42-浓度与现代大气压沉积的蒸散（ET）因子大约7-40的浓度相似。更新世补给的大多数ET值几乎是全新世补给的ET值的两倍。 NO3- / Cl-和ClO4- / Cl-的比率比Br- / Cl-或SO4（2-）/ Cl-的比率更具可变性。认为在全新世的最干旱条件下已充满电的样品具有相对较高的NO3 Cl-比率和较低的N-15值（每密耳+1（每千分之一）），类似于现代大容量大气N沉积。 NO3的δO-18值（千分之四至0）表明，大气中的NO3并未直接传播到地下水中，而是在渗透之前已在土壤中循环。具有接近大气NO3- / Cl-比的样品具有相对较高的ClO4-浓度（1.0-1.8μg / L），具有几乎恒定的ClO4- / Cl-摩尔比（1.4 +/- 0.1）x 10（-4） ，这与新北中北部晚新世末期大气总体沉积中ClO4-的平均浓度为0.093 +/- 0.005μg / L一致。被认为在潮湿条件下充电的样品比最可能保存的样品具有更高的值（δN-15值（每千份中+3至+8份），较低的NO3- / Cl-比和较低的ClO4- / Cl-比。在补给之前，土壤中可能已经从大气中吸收了NO3的过程也可能在不同程度上消耗了ClO4-。如果这些解释是正确的，则大气中ClO4-的浓度高达4μg / L。在ET接近40的西南部分的人为来源的地下水中可能发生。在ET大于40的干旱地区下，补给下的补给中可能会发生未污染的地下水中较高的ClO4-浓度，那里的长期盐分突然从大气中逸出干燥的土壤，或存在其他（非大气）ClO4-天然来源的地方。

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