Decadal shifts in groundwater age detected by environmental tracers across California, USA
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Abstract
Groundwater age offers important insight into recharge, storage, and contamination risk. Although models predict age changes can be driven by pumping and climate variability, direct observational evidence remains limited. Here, we analyzed paired environmental tracer suites (tritium, carbon-14, and tritiogenic helium-3) collected a decade apart from 268 wells across California to assess the prevalence of groundwater age transience. Travel-time distribution models and statistical tests indicated age transience at 29% of sites, occurring most often in agricultural regions, such as the San Joaquin Valley and Southern Coast Ranges, where large carbon-14 changes coincided with substantial nitrate and chloride shifts. Sites with tritiogenic helium-3 data showed more frequent age transience, underscoring the value of multi-tracer data sets. These results provide the first regional evidence of widespread groundwater age change and a method for detecting changing water balances with implications for groundwater sustainability and water quality.
Suggested Citation
Jurgens, B.C., and Levy, Z.F., 2026, Decadal shifts in groundwater age detected by environmental tracers across California, USA: Geophysical Research Letters, v. 53, no. 6, e2025GL119794, 12 p., https://doi.org/10.1029/2025GL119794.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Decadal shifts in groundwater age detected by environmental tracers across California, USA |
| Series title | Geophysical Research Letters |
| DOI | 10.1029/2025GL119794 |
| Volume | 53 |
| Issue | 6 |
| Publication Date | March 23, 2026 |
| Year Published | 2026 |
| Language | English |
| Publisher | American Geophysical Union |
| Contributing office(s) | California Water Science Center |
| Description | e2025GL119794, 12 p. |
| Country | United States |
| State | California |