Dating Groundwater: A Short Review
Dating Groundwater: A Short Review
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地下水约会：简短回顾
DOI：
10.1021/bk-1982-0176.ch011
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发表时间：
1982
期刊：
影响因子：
--
通讯作者：
H. Bentley
中科院分区：
文献类型：
--
作者：
S. Davis;H. Bentley
地下水的年龄是水与大气隔离的时间长度。从理论上讲，年龄可以通过以下方式估算：（1）根据达西定律结合连续性方程计算的地下水从补给点到地下感兴趣点的旅行时间，（2）与大气接触进入水中的放射性核素的衰变，（3）地下放射性反应产物的积累，（4）放射性核素及其放射性子产物之间的不平衡程度，（5）溶解在水中的化合物的分子结构随时间的变化，（6）地下水中人造物质的存在，（7）水中古气候指标与已知的过去气候年表的相关性，以及（8）存在或不存在与先前已经定年的过去地质事件有关的离子。由于每种方法都存在不确定性，因此应在每种实地情况下使用尽可能多的方法。由于水动力弥散和分子扩散总是发生的，一个给定的地下水样品的单一的精确年龄是不存在的。然而，用各种方法测定样品的“年代”，将有助于确定分散和扩散的程度，以及发生在许多威尔斯内的各种含水层的水的混合情况。如果分散、扩散和交叉混合是最小的，那么在理想的条件下，可以确定沃茨的年龄小于30，000年，粗略估计的年龄可能达到100万年。
The age of groundwater is the length of time the water has been isolated from the atmosphere. Theoretically, ages can be estimated by (1) the travel time of groundwater from the point of recharge to the subsurface point of interest as calculated by Darcy's law combined with an equation of continuity, (2) the decay of radionuclides which have entered the water from contact with the atmosphere, (3) the accumulation of products of radioactive reactions in the subsurface, (4) the degree of disequilibrium between radionuclides and their radioactive daughter products, (5) the time-dependent changes in the molecular structure of compounds dissolved in water, (6) the presence of man-made materials in groundwater, (7) the correlation of paleoclimatic indicators in the water with the known chronology of past climates, and (8) the presence or absence of ions which can be related to past geologic events that have been previously dated. Owing to uncertainties in each of the methods, as many methods as possible should be used in every field situation. Because hydrodynamic dispersion and molecular diffusion always take place, a single precise age for a given groundwater sample does not exist. "Dating" the sample by various methods, however, will help determine the extent of dispersion and diffusion as well as mixing of water from various aquifers which takes place within many wells. If dispersion, diffusion, and cross-mixing are minimal, then under ideal conditions ages can be determined for waters less than about 30,000 years old, and rough approximations of ages up to about one million years appear possible.