Any experimentalist knows that once such a technique is dropped, although the principles may be easily recovered, there will have to be an enormous investment of time to recover the art. This loss of expertise, in the case of CFC analysis, raised a barrier that forestalled most researchers who considered carrying on the method. A second major impediment was presented by the nature of the research funding process.
Developing the art as well as the science of the analytical method is time consuming; the at that time standard two-year grant required almost yearly new proposals, often before much demonstrable progress had been made. Without research funding programs directed specifically at hydrology, the proposals for continued funding had to compete with a very wide range of geochemical research projects.
Geochemical analysis is instrumentation intensive, and some laboratories have succeeded in building up facilities worth millions of dollars. At least some of these laboratories took the viewpoint that the topics they researched were fundamentally so much more important than hydrological tracing that, in comparison, the new method did not deserve support.
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Expressed through the medium of proposal reviews, these opinions were successful in preventing continued funding for the research. Without being constrained by having to provide immediate results and without having to regularly run the gauntlet of hostile reviewers from other disciplines, they had the opportunity to systematically address the development of the method and present it to the hydrological community in a fairly mature state.
The final factor that must also be mentioned is vision. Once a new geochemical method fails to reach fruition, even if this is due largely to circumstance rather than its merits, the huge investment of time and labor necessary to reinvent it raises a high barrier. It takes a researcher with a strong vision of the potential reward to take the risk of losing that investment. In the early s I received a telephone call from an external reviewer for the U. Department of Energy plan of investigations at Yucca Mountain.
The reviewer told me about the planned collection of 36 Cl samples from the exploratory shaft under the mountain. Ratios higher than this value were considered indicative of very rapid infiltration of 36 Cl fallout from nuclear weapons testing in the s.
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I had no connection with the Yucca Mountain project, but the reviewer had contacted me as an independent authority on hydrological applications of 36 Cl. When asked why she was so concerned about this particular aspect of the proposed investigations, she replied that it was considered the single most critical component of the entire range of research at the site, since the widespread presence of bomb 36 Cl would show that unsaturated fluxes were much greater than anticipated.
In fact, when the 36 Cl results came in Fabryka-Martin et al. However, instead of indicating that bomb 36 Cl was entering every-. Reprinted, with permission, Levy et al. Why the new interpretation? It was because a long-term history of much higher cosmogenic 36 Cl production had in the meantime been established through an entirely independent and quite unconventional research project. This shift was attributed to increased 14 C production during that period, resulting from an increased cosmic-ray flux, which in turn was attributed to a weakened dipole geomagnetic field Mazaud et al.
After reading that paper, I realized that 36 Cl could potentially address the problem because it has a very short residence time in the atmosphere and essentially falls directly out onto the land surface. A record of 36 Cl deposition should therefore be much closer to a direct record of variations in cosmogenic production. The difficulty was finding an archive in which 36 Cl deposition would be preserved, inasmuch as it is extremely mobile in the presence of water.
United States Betancourt et al. This experiment was proposed to the NSF and, after some initial difficulties, was funded. Midden samples from western and southern Nevada were obtained through the cooperation of Peter Wigand at the Desert Research Institute in Reno.
The initial results were successful, and in a few years a sketchy preliminary history of 36 Cl deposition was reconstructed. The major feature of this reconstruction was a pattern of relatively low ratios during the Holocene i. The significance of this result was immediately apparent to those involved in the Yucca Mountain project.
The right information happened to appear just.
Furthermore, it is obvious that this temporal variation in 36 Cl fallout can serve as a hydrological tracer in many other similar circumstances. The contrast with the development of the CFC tracer method could hardly be more striking. Why was the secular variation 36 Cl tracer springing into existence just as it was needed, while the CFC tracer sat on the shelf for years after its capabilities had been highlighted? The most obvious answer has to do with research funding. Although the basic idea would undoubtedly have made a fine target for one of Senator Proxmire's ''Golden Fleece" awards were he still alive, reviewers and program managers were able to see that it was a means to obtain critical data that could not be had otherwise.
Other factors played a role. The "art" of 36 Cl analysis was maintained through long-term funding of the PRIME Lab accelerator mass spectrometry NSF facility at Purdue University and at my own laboratory, overcoming the inevitable start-up problems that stall the acquisition of real results. The state of research on environmental tracers in ground water hydrology is flourishing. New tracers are being developed, tracer results are being applied more and more widely as integral parts of hydrological investigations, and results of environmental tracer studies are being applied to fields outside hydrology.
What can be done to promote continued growth of the field? Two case studies with remarkably contrasting histories were examined in order to reflect upon this question. Two studies cannot be presumed to yield any definitive patterns, but some common threads can be discerned:. Vadosezone techniques for estimating ground-water recharge in arid and semiarid regions. Calibration of the 14 C timescale over the past 30, years using mass spectrometric U-Th ages from Barbadoscorals. Van Devender, and P.
Basics of 3H/3He dating
The Last 40, Years of Biotic Change. University of Arizona Press. Combined use of groundwater dating, chemical, and isotopic analyses to resolve the history and fate of nitrate contamination in two agricultural watersheds, Atlantic coastal plain, Maryland. The alluvium and terrace system of central Oklahoma. A tracer study of the Floridan aquifer in southeastern Georgia: Implications for groundwater flow and paleoclimate.
Distribution of chlorine in the unsaturated zone at Yucca Mountain: An indicator of fast transport paths. September 26—29, , Las Vegas, Nevada.. Los Alamos National Laboratory. Water movement in desert soil traced by hydrogen and oxygen isotopes, chloride, and chlorine, Southern Arizona.
Geomagnetic field control of 14 C production over the last 80 ky: Implications for the radiocarbon time scale. Strontium, boron, oxygen, and hydrogen isotope geochemistry of brines from basal strata of the Gulf Coast sedimentary basin, USA. Geochemical estimates of paleorecharge in the Pasco Basin: Evaluation of the chloride mass balance technique.
Regional ground-water mixing and the origin of saline fluids: Opportunities in the Hydrologic Sciences. Environmental tracers for water movement in desert soils of the American Southwest. Chlorine in fossil rat urine: An archive of cosmogenic nuclide deposition during the past 40, years. Evaluation of liquid and vapor water flow in desert soils based on chlorine and tritium tracers and nonisothermal flow simulations.
Chemical and isotopic constraints on evolution and migration. Paleotemperatures in the southwestern United States derived from noble gases in ground water. A possible tracer and indicator of groundwater age. Fluorocarbon tracers in hydrology. Soil-water flux in the southern Great Basin, United States: Temporal and spatial variations over the last , years. Continuous ,year climate record from vein calcite in Devils Hole, Nevada.
Hydrologic science, an important, interdisciplinary science dealing with the occurrence, distribution, and properties of water on Earth, is key to understanding and resolving many contemporary, large-scale environmental issues. The Water Science and Technology Board used the opportunity of its Abel Wolman Distinguished Lecture to assess the vitality of the hydrologic sciences by the hydrologic community. The format included focus by lecturer Thomas Dunne on the intellectual vitality of the hydrologic sciences, followed by a symposium featuring several invited papers and discussions.
Hydrologic Sciences is a compilation of the Wolman Lecture and the papers, preceded by a summarizing overview. The volume stresses a number of needs for furtherance of hydrologic science, including development of a coherent body of transferable theory and an intellectual center for the science, communication across multiple geo- and environmental science disciplines, appropriate measurements and observations, and provision of central guidance for the field.
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Introduction to Water Dating and Tracer Analysis
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