Water sources in riparian trees of the southern Appalachian foothills, USA: A preliminary study with stable isotope analysis

Abstract The aim of this study was to determine the sources of water uptake for two common riparian tree species found in the southeastern United States, Acer negundo and Betula nigra. The study site was located within a riparian zone typical of this region and those of the temperate USA. Water sources were determined by analyzing signatures of stable isotopes found naturally in water, 2H and 18O. Samples from surface water, groundwater, and soil, plus woody tissue from mature individuals of each species, were taken once each month during the 2011 summer growth season. Both species relied strongly on an unidentified ground water source, although A. negundo also showed a strong correlation with deep soil moisture (r2 = 0.972). Sampling limitations did not permit an accurate determination of the fractional contribution of each source to plant water, limiting the strength of the results. The evidence collected leads to conclusions comparable to those of studies that have been conducted in arid parts of North America, corroborating that streamside species may rely heavily on groundwater sources, not surface streamwater. Further studies are needed in this region to confirm the evidence reported here to establish a baseline for vegetation in these systems.