Restoration as experimental manipulation: Is channel structure or watershed condition more important in predicting ecosystem function in urban streams?

The science of stream restoration is young and rapidly evolving.  A topic of particular interest is whether site-scale management can compensate for watershed-scale impacts, as are seen in urban stream systems.  Reconfiguration of channel shape is a common form of stream restoration, particularly in the southeastern United States.  For stream ecologists, it is a convenient experiment for exploring the effects of channel structure on ecosystem functions such as nutrient uptake and whole stream metabolism.  We are comparing these response variables between four urban stream restoration projects, four unrestored urban streams and four minimally impacted forested sites in the Piedmont, North Carolina, USA.  If stream restoration works as intended, measurements and estimations of ecosystem function at the restored sites would be expected to fall on a trajectory between unrestored urban sites and forested sites.  Our data suggest that restoration projects are unable to effectively compensate for watershed-scale degradation (e.g. urbanization associated hydrologic alterations and eutrophication are better correlates of ecosystem function than restoration status) and that the restoration process itself can shift ecosystem structure off the intended recovery trajectory (e.g., restored urban streams had reduced canopy cover and more homogenous substrate and flow habitat conditions relative to their unrestored, urban counterparts).  These data suggest important considerations for improved site selection and restoration design in urban watersheds.