The Effects of Dual-Domain Mass Transfer on the Tritium−Helium-3 Dating Method
详细信息 查看全文
- 作者：Rebecca B. Neumann ; Eric M. LaBolle ; Charles F. Harvey
- 刊名：Environmental Science & Technology
- 出版年：2008
- 出版时间：July 1, 2008
- 年：2008
- 卷：42
- 期：13
- 页码：4837 - 4843
- 全文大小：2698K
- 年卷期：v.42,no.13(July 1, 2008)
- ISSN：1520-5851
文摘
Diffusion of tritiated water (referred to as tritium) and helium-3 between mobile and immobile regions in aquifers (mass transfer) can affect tritium and helium-3 concentrations and hence tritium−helium-3 (3H/3He) ages that are used to estimate aquifer recharge and groundwater residence times. Tritium and helium-3 chromatographically separate during transport because their molecular diffusion coefficients differ. Simulations of tritium and helium-3 transport and diffusive mass transfer along stream tubes show that mass transfer can shift the 3H/3He age of the tritium and helium-3 concentration ([3H + 3He]) peak to dates much younger than the 1963 peak in atmospheric tritium. Furthermore, diffusive mass-transfer can cause the 3H/3He age to become younger downstream along a stream tube, even as the mean water-age must increase. Simulated patterns of [3H + 3He] versus 3H/3He age using a mass transfer model appear consistent with a variety of field data. These results suggest that diffusive mass transfer should be considered, especially when the [3H + 3He] peak is not well defined or appears younger than the atmospheric peak. 3H/3He data provide information about upstream mass-transfer processes that could be used to constrain mass-transfer models; however, uncritical acceptance of 3H/3He dates from aquifers with immobile regions could be misleading.