For more than six decades, local scientists have collected sugar maple leaves from Gatineau Park to measure their radiocarbon levels, creating the longest continuous record of its kind. Now, a study of those leaves led by the André E. Lalonde National Facility for Accelerator Mass Spectrometry (AEL-AMS) located at the University of Ottawa shows that the effects of Cold War–era nuclear weapons testing have only recently disappeared from the local biosphere. The study, titled “Stored carbohydrates buffer Bomb and Suess radiocarbon effects in maple leaves across a 65-year Ottawa region record,” was published in Scientific Reports.

The Geological Survey of Canada began collecting maple leaves in Gatineau Park in 1961, taking samples once a month during each growing season. Its scientists analyzed the leaves until the agency’s radiocarbon laboratory closed in 2004. The AEL-AMS later took over the analyses and extended the record through 2025, adding 59 annual and seasonal measurements. The collection is ongoing, though leaves gathered in September 2026 are not included in the current study.

“These leaves are a 65-year diary of the atmosphere,” explains Dr. Leonard Wassenaar, executive director of the André E. Lalonde National Facility for Accelerator Mass Spectrometry (AMS) at the University of Ottawa. “It took more than 65 years for the extra radiocarbon from weapons testing to disappear from the Ottawa-area biosphere. The effects were still with us decades after the last test.”