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We describe a method to determine the nitrogen and oxygen isotopic composition of nitrate in groundwater samples (N/N and O/O, respectively), which is based on the analysis of nitrous oxide gas (NO) that is produced quantitatively from nitrate by denitrifying bacteria. This method which is simple, inexpensive and effective in the removal of nitrite is greatly selective for NO and was used for mixed samples containing both NO and NO with little or no measurable cross-contamination. The precision of δN and δO are 0.3 and 0.17 ‰ respectively, compared to that of 0.1 and 0.5 ‰ abroad (Brand et al. in Org Geochem 21:585-594, ; Begley and Scrimgeour in Anal Chem 69(8): 1530-1535, ; Kornexl et al. in Rapid Commun Mass Spectrom 13(16):1685-1693, ; Böhlke et al. in Rapid Commun Mass Spectrom 17:1835-1846, ; Gehre and Strauch in Rapid Commun Mass Spectrom 17(13):1497-1503, ; Werner in Isot Environ Health Stud 39:85-104, ). [ABSTRACT FROM AUTHOR]

Chlorine-36 has various advantages as a dating tool for old groundwater. In this paper,36Cl of Quaternary groundwater in the Hebei plain of North China has been measured using accelerator mass spectrometry (AMS). Ages calculated from the36Cl/Cl ratio show that ion filtration, which is responsible for the Cl concentration increasing with depth and along flow paths in Hebei plain groundwater. It is concluded that36Cl age of the groundwater in the 3rd Group of the Quaternary (Q2) in the Cangzhou area is 250ka, and that of the 4th Group(Q1) is 300 ka. [ABSTRACT FROM AUTHOR]

There are great scientific interests to reveal the shallow brine genesis in different geologic environments and also practical significance for resource production and environmental protection, which have not yet gained much attention, however. This study took shallow Quaternary brine in the coastal plain of Laizhou Bay and salt lake brine/intercrystalline brine in arid inland Qaidam Basin in China as two kinds of representative shallow brines, and comparatively analyzed the Cl stable isotopic signatures, coupled with hydrochemistry and water isotopes, aiming at finding out the salinity origin of shallow brines in the coast and inland basin, and further discussing Cl stable isotopic behavior in actual hydrogeological systems. The results indicated that shallow brine in the coastal zone originated from evaporation and precipitation formerly, and halite dissolution by tidewater or rainwater later, as a result of which, most of shallow brine exhibited enriched Cl isotopic signatures. As a contrast in arid inland basin, superficial brine originated from the dissolution of precipitated salt minerals by river water formerly, and intensive evaporation with subsequent precipitation in basin center later, for which all the brines finally exhibited the depleted Cl isotopic signatures. In addition, diffusion and ion filtration in the coast zone, and inflow of deep oilfield water in inland basin, were proposed as potential processes contributing to respective Cl isotopic signatures. In the coast, 37 Cl are enriched and 81 Br are depleted in most of shallow brines, while all the superficial brine (saline water) samples in arid inland basin exhibit negative δ 37 Cl and positive δ 81 Br values. Precipitation and dissolution of salt minerals were believed to contribute primarily to the contrary isotopic signatures, which would not change the Br isotopic compositions a lot for the solution in which the original Br concentration has been relatively high, which is not the case for Cl isotope, however. [ABSTRACT FROM AUTHOR]