Figure 2.

Comparison of ¹⁸O isotopic signatures on two dates for stem water of plants at the surface of the Powell’s Cave site with the signatures of water from surface soil (surface to bedrock) and from an 18-m-deep underground stream (mean ± SEM; n = 2–5). The species sampled were Abutilon fructicosum (a forb), Aristida purpurea (a grass), Guttierezia dracunculoides (a subshrub), and Q. fusiformis Small (live oak tree), and the two sampling dates were October 25, 1997 and June 27, 1998 (the cave is open only on the last weekends of February, June, and October). Isotopic analyses were run at the Stable Isotope Research Facility of the University of Utah. Water in the stems of live oaks at the surface had an ¹⁸O signature that closely matched the underground stream water, evidence that the trees are likely using this water as a primary source.