Invasive species can have ecosystem effects that span aquatic-terrestrial boundaries.  We investigated the effects of an invasive riparian tree, Russian olive (Eleagnus angustifolia), on the ecosystem function of a desert spring stream, Deep Creek, Idaho.  Reaches of Deep Creek were studied in the early 1970s and it became recognized as an archetypal autotrophic stream.  One reach has since been invaded by Russian olive, setting the stage for a unique before-after-invasion-control comparison.  We repeated measures of community metabolism (open-channel technique) and allochthonous inputs in invaded and control reaches during summer-fall 2006.  P/R at the control site was similar to estimates from 1971.  In contrast, P/R decreased by 42% (1.37 to 0.79) at the invaded site, a change that may have been largely driven by increased respiration.  If so, this change in trophic status may be associated with the more than 10-fold increase in allochthonous input we observed at the invaded site.  Yet, a leaf-pack experiment showed that Russian olive leaves had slower decay rates compared to native species, suggesting they provide poor quality organic matter.  We are constructing an annual carbon budget and using stable isotopes to further assess the effects of this invasion on energy flow and food web structure.