Nuclear Legacy Fades After 65 Years

A study of sugar maple leaves from Gatineau Park has found that the effects of Cold War-era nuclear weapons testing have only recently disappeared from the local biosphere. The research, which analyzed leaves collected over a 65-year period, showed that radiocarbon levels took over 65 years to return to normal.

The Geological Survey of Canada began collecting maple leaves in Gatineau Park in 1961, creating the longest continuous record of its kind. The collection of leaves was taken over by the André E. Lalonde National Facility for Accelerator Mass Spectrometry (AEL-AMS) in 2004, which extended the record through 2025. The radiocarbon level in the leaves peaked in 1964 at 842 parts per thousand above the reference level.

By 2025, the radiocarbon level in the leaves had fallen to –13.9 parts per thousand, indicating that the effects of nuclear testing had finally begun to fade. The above-ground nuclear tests conducted in the late 1950s and early 1960s by countries including the United States, the Soviet Union, the U.K., France, and China released large amounts of radiocarbon into the atmosphere, roughly doubling global levels.

The study of the maple leaves, published in Scientific Reports, used the leaves as bioarchives to measure the radiocarbon levels in the atmosphere over time. The leaves absorb carbon dioxide that is turned into sugars used for the tree's growth, preserving information about the atmosphere at the time. The research provides a unique insight into the legacy of nuclear testing and its impact on the environment.

## Why it matters The study highlights the long-lasting impact of nuclear testing on the environment. The fact that it took over 65 years for the radiocarbon levels to return to normal shows that the effects of nuclear testing can persist for decades after the tests themselves have stopped. This has significant implications for our understanding of the environmental impact of nuclear testing and the importance of monitoring and mitigating its effects.

The collection of maple leaves in Gatineau Park is ongoing, with the exception of leaves gathered in September 2026, which are not included in the current study. The research will continue to provide valuable insights into the environmental impact of nuclear testing and the legacy of the Cold War era.