2006 Fiscal Year Final Research Report Summary
Evaluation of the role of groundwater in the global water circulation using environmental tracers of natural radionuclide and dissolved noble gases.
| Project/Area Number |
16310009
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Environmental dynamic analysis
|
|---|
| Research Institution | Kyoto University |
|---|
Principal Investigator |
MAHARA Yasunori Kyoto University, Research Reactor Inst., Professor, 原子炉実験所, 教授 (30371537)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
KUBOTA Takumi Kyoto University, Research Reactor Inst., Assistant Prof., 原子炉実験所, 助手 (90335240)
NAKANO Tomoko Kyoto University, Research Reactor Inst., Assistant Prof., 原子炉実験所, 助手 (30373020)
|
|---|
| Project Period (FY) |
2004 – 2006
|
| Keywords | Dissolved 4He concentration / ^<36>Cl concentration / Groundwater residence time / Water circulation rate / Radium isotopic ratio / Shallow groundwater / Deep groundwater / Freshwater resources |
|---|
| Research Abstract |
We evaluated the measurement technique for ^<36>Cl with very low concentration in deep groundwater using an accelerator mass spectrometer through competitive analyses among ANU, ETH and Purdue. The data measured at every three laboratories are acceptable for very old groundwater dating in deep strata. We proposed the new method of dating for very old groundwater over one million years using excess dissolved ^4He concentration calibrated with 36Cl concentration. Furthermore, we reveal the criteria to judge stagnant water stored in strata as the fossil water using the method.
The most important freshwater resources are river water and shallow groundwater with short residence time ranging from a few months to 1000 years for the human activities. Basically, the basic river water is consisted of the seepage groundwater with a short residence time. The precise ^3H+^3He dating method has already been demonstrated for young groundwater with residence time of less than some ten years. The re is
… More
no authorized dating technique to estimate residence time ranging from 100 years to 1000 years. We proposed the new method using the radium isotope ratio and its concentration and verified the method with the published data of shallow groundwater and hot springs collected in the past studies.
We estimated the residence time in various groundwater environments using natural environmental radionuclide and dissolved noble gases as the environmental tracers. We can categorize groundwater in the global water circulation into two groups, which one is almost fresh and shallow groundwater with less than some ten years and the other is saline and stagnant water with very old over 10^5 or 10^6 years. The fresh and young groundwater is greatly contributed to the global water circulation, but saline stagnant water probably plays out of role in it. However, we can not simply judge groundwater movement from only depth, location and permeability in the basin The most important thing is the historical formation and structure of the groundwater basin for the groundwater circulation. Less
|
