| Autor: |
Chmielarski, M., Dogramaci, S., Cook, P. G., McCallum, J. L. |
| Předmět: |
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| Zdroj: |
Geophysical Research Letters; 12/16/2022, Vol. 49 Issue 23, p1-11, 11p |
| Abstrakt: |
Analyzing groundwater systems in transient state is essential for understanding the response of groundwater recharge to changing environments. Radioactive isotopes have long been used to track recharge behavior, typically under steady state conditions. This study tests the limitations of using radioactive isotopes in confined aquifers and under transient conditions to sense changes in groundwater recharge rates over time. Four system parameters determine the bounds of this approach: the isotope half‐life, the Péclet number (Pe), and mobile‐immobile zone interactions. This study revealed that in confined groundwater systems where Pe ≥ 10, isotopes reflect transience when the half‐life matches the water travel time down the flow path or the time elapsed from the change in velocity. This response is evident regardless of mobile‐immobile interaction, suggesting that appropriate isotope selection is key to establishing past recharge regardless of aquifer lithology or geometry. Plain Language Summary: Changes in groundwater recharge are linked to environmental stimuli. Defining these changes helps inform a holistic understanding of the system, and guides sustainable approaches to groundwater use. The use of radioactive elements for examining long‐term groundwater behavior is common due to their time‐related quality. However, this is rarely done in the context of changing recharge conditions. The main purpose of this study was to observe the radioactive elements' response under a variety of groundwater flow and subsurface geometry settings to determine under which conditions they uncover past changes in groundwater recharge. The physical parameters of the system are often simplified, but robust enough to explore where the limitations of this application lie. Radioactive elements reflect change when the half‐life is equal to the time it takes the groundwater to travel down the flow path, regardless of the physical subsurface settings. This makes the framework highly useful for interpreting real data sets. Key Points: Radioactive isotopes preserve transient groundwater behavior with timeframes consistent with their half‐lifeTransient behavior can be identified using a visual interpretation of a log‐scaled change in concentration with distance plotGraphical interpretation allows determination of the timing of an environmental change influencing groundwater recharge [ABSTRACT FROM AUTHOR] |
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