Trace metals in trees of the Tahoe basin

Techniques for determining site-specific histories of trace metals are important for understanding the periodicity of natural events and the human impact on our environment. In this study we utilized dendrochemistry for establishing a historical record of trace metals in Jeffrey pines (Pinus jeffreyi ). Methods were developed for using high resolution Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and paired coring of live trees. Two sites were chosen in the Lake Tahoe Basin with similar abiotic and ecologic attributes, one proximal to a heavily traveled highway and the other isolated from any local source of auto emissions. Both sites are influenced by the same winter storm track and have experienced recent fire events. Two cores from each of two trees at the two sites were analyzed providing a method of comparison within, and between, trees and sites. The effectiveness of this technique for broad scale investigations was evaluated by comparing the concentrations between cores with available data for historic trends of auto emissions and lead deposition. Lead concentrations at both sites were generally below or near method detection limits (MDL), and the concentration distribution showed little relationship to the historic pattern of tetraethyl lead emissions. Eleven other elements were measured and represent three distinctive groups of trace metal distribution. Many of these elements follow patterns observed in other species and appear to be a function of complex environmental interactions.