Rebecca A. Stolar, Thomas Meixner, Kiyomi Morino, and Steve Leavitt
Summer floods are an important source of sustained streamflow in arid and semi-arid rivers of the American Southwest and Northwest Mexico. How much of this importance is a natural function of these systems versus an artifact of human alterations to the system is not known. Environmental information in the tree ring cellulose of Populus can be used to investigate the variation in water sources over time in these areas. Past research has shown that streamflow sources in the San Pedro Basin of Arizona vary isotopically between a source water of basin ground water and a summer flood water source. This study uses isotopic analyses of Populus fremontii and atmospheric data in the San Pedro Basin to determine the water source of the trees and the river water source condition. After analyzing weather data within the basin, an inversion of the Barbour model using tree ring cellulose isotopes was used to obtain the water source isotopic composition. The variation in water source composition as inferred from the model was then compared to the river composition over time. By drawing this comparison, it aides in anticipating consequences from human driven modification including climate change on the river systems.