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Using Tree Rings to Determine the Age of Groundwater Contamination

By Everett & Associates on Oct 24, 2012 at 12:27 PM in Environmental Issues

The application of dendroecology to environmental forensics is an exciting development because the method comes with a built in calendar for dating contamination events: tree rings! 

As tree roots draw in shallow groundwater to nourish the tree, any impurities in the water are incorporated into the wood of the growing tree. Advances in analytical chemistry now allow researchers to measure the tiny traces of contaminants on a tree ring-by-tree ring basis. In this way, trees can document the impact of soil and groundwater contamination.

If the tree is downgradient from the release point of contamination, age-dating with precision to the year is possible. This is done by identifying a peak in an element associated with the released chemical (e.g., chlorine for chlorinated solvents or sulfur for middle petroleum distillates) and determining the age of the corresponding ring. Often performed on wood from stumps, this work can easily be performed on live trees by collecting a pencil-width core from the trunk. This coring technique has been employed by foresters for decades and does not harm the tree.