409 Riparian Dendrochemistry: Detecting Anthropogenic Gadolinium in Trees along An Effluent Dominated Desert River

Friday, November 6, 2009: 10:00 AM
Santa Fe (Camino Real Hotel)
Amy L. McCoy , Arid Lands Resource Sciences, University of Arizona, Tucson, AZ
Paul R. Sheppard , Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ
Tom Meixner , Soil, Water and Environmental Science Department, University of Arizona, Tucson, AZ
Barron J. Orr, PhD , Office of Arid Lands Studies, University of Arizona, Tucson, AZ
This research documents spatial and temporal patterns of effluent uptake by riparian trees through development of a new and innovative application for dendrochronology, specifically dendrochemistry. The rare-earth element (REE) gadolinium (Gd), is a known micro-pollutant in its anthropogenic form and enters streams from wastewater treatment plants. Anthropogenic Gd was first used in select medical procedures in 1988 and subsequently discharged via treatment plants into waterways. Riparian trees that utilize surface and groundwater uptake anthropogenic Gd, but do not utilize it, thereby providing a general presence/absence date stamp in tree rings and making it an ideal marker for this dendrochronological study. Results from this study along the Upper Santa Cruz River in southeastern Arizona show elevated levels of Gd in effluent-dominated surface flows, confirming that anthropogenic Gd is present. Gd was found in the growth rings of Fremont cottonwood trees (Populus fremontii) that are growing in the floodway adjacent to the effluent-dominated portion of the stream. The presence of Gd in cottonwood annual rings suggests that the trees are utilizing effluent over the course of the growing season. Furthermore, Gd concentration patterns in trees directly adjacent to the stream may be reflective of high-frequency changes in surface water quality. Information on the impacts of effluent quality on the chemical composition of tree rings can be a useful monitoring tool to evaluate the spatial and temporal patterns of effluent use in riparian trees and diffusion of effluent throughout the system.