Trees as monitors of tritium in soil water

Tritium (³H) activities in the foliage of forest trees were found to reflect ³H activities in soil water along the perimeter of a retired low-level radioactive waste disposal site. Spatial variability in foliage ³H activity clearly delineated patterns of ³H in soil water as deep as 3 m. Late summer increases in foliage ³H activity paralleled increases in soil water activity and also suggested greater uptake of water from deep reservoirs after surface soils had dried out. White and chestnut oak (Quercus alba L. and Q. prinus L.) dominated the study area and were good monitors of ³H, regardless of tree size. Spatial patterns of ³H in foliage of these species over a 5-ha watershed were interpretable in terms of the local landscape and the probable pathways of movement of contaminated water originating on the disposal site. Results of this study suggest that trees and other deeply rooted plants may serve as simple and effective monitors of soil water contamination and may therefore be useful additions to permanent monitoring systems.