Gatineau Park foliage reveals local Cold War nuclear testing legacy

For over six decades, researchers have been collecting sugar maple leaves from Gatineau Park to monitor changes in their radiocarbon levels, creating the longest continuous record of its kind. A recent study, led by the André E. Lalonde National Facility for Accelerator Mass Spectrometry (AEL-AMS) at the University of Ottawa, analyzed the leaves to reveal that the impact of Cold War nuclear weapons testing on local radiocarbon levels persisted until very recently.

Published in Scientific Reports, the study titled "Stored carbohydrates buffer Bomb and Suess radiocarbon effects in maple leaves across a 65-year Ottawa region record" provides new insights into how the effects of nuclear testing gradually disappeared from the biosphere. The Geological Survey of Canada initiated the leaf collection in 1961, with monthly sampling during the growing season, a process continued until the agency's radiocarbon laboratory closed in 2004.

The AEL-AMS then took over, extending the record through 2025. Dr. Leonard Wassenaar, executive director of the AEL-AMS, explains that it took more than 65 years for the excess radiocarbon from weapons testing to dissipate from the Ottawa-area biosphere. The study found that while leaves absorb carbon dioxide that becomes part of the tree's growth, the radiocarbon in each leaf sample accurately preserves the atmospheric conditions at the time of absorption.

The researchers discovered that the radiocarbon in Gatineau Park leaves lagged atmospheric changes by approximately 2.2 years, a gap attributed to the use of stored carbon from previous seasons. This finding has significant implications for interpreting radiocarbon measurements from plant material, as it will help refine atmospheric reconstructions based on these samples.