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Chlorine 36 and tritium from nuclear weapons fallout as tracers for long‐term liquid and vapor movement in desert soils
Author(s) -
Phillips Fred M.,
Mattick Julie L.,
Duval Thomas A.,
Elmore David,
Kubik Peter W.
Publication year - 1988
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr024i011p01877
Subject(s) - advection , soil water , tracer , chlorine , tritiated water , dispersion (optics) , water vapor , chemistry , atmosphere (unit) , accelerator mass spectrometry , groundwater , environmental science , environmental chemistry , hydrology (agriculture) , tritium , soil science , mass spectrometry , meteorology , nuclear physics , geology , physics , geotechnical engineering , organic chemistry , chromatography , optics , thermodynamics
Chlorine 36 and 3 H have been widely used as laboratory tracers for the advection and dispersion of anionic solutes and water, respectively. Advances in accelerator mass spectrometry have recently made possible the analysis of 36 Cl in natural soil water samples. Field investigations analogous to the laboratory experiments can now be conducted. Pulses of 36 Cl and 3 H released into the atmosphere by nuclear weapons testing in the 1950s and 1960s serve as the tracers. We report 36 Cl and 3 H measurements on desert soil profiles from New Mexico. In both cases where the two tracers were measured in the same profile, the 3 H bomb pulse had penetrated between 1 and 3 m, but much of the 36 Cl was retained near the soil surface. In contrast, the laboratory experiments usually show more rapid movement of 36 Cl than 3 H due to the anion exclusion effect. We attribute the difference to the lower water content, fluctuating temperature gradients, and longer time scale of the field situation, which may enhance vapor movement of the tritiated water relative to solute advection of the 36 Cl. The spreading of the 36 Cl and 3 H pulses may be modeled by dispersivities ranging from 5 to 8 cm, much larger than most corresponding laboratory values. These larger apparent dispersivities are probably more a result of vertical velocity fields varying with depth and time than of soil heterogeneity. These results illustrate how the bomb pulse 36 Cl and 3 H can be useful links between laboratory solute transport studies and the corresponding field applications.