Measuring food web responses to restoration using stable isotopes

Fossil Creek provides a model ecosystem for studying restoration because two major threats have been reversed. Exotic fish have been removed from a large section of the river and flow was restored, after a century of diversion, as part of a large dam removal program. We used stable isotopes prior to restoration to study how the food web was affected by the water diversion and the presence of exotic fish. We repeated isotope collections three years following restoration to test how food web structure responded to restoration. Pre-restoration studies indicate that fish living in pristine sites relied more on algal productivity than fish in deteriorated sites. Both carbon and hydrogen isotope values indicated a significant shift in the food base with water diversion, however the error around estimates based on hydrogen data is smaller. Nitrogen isotopes revealed that native fish fed lower on the food chain in the presence of exotic bass and sunfish. In combination with population studies of target species, stable isotope studies can reveal how entire food webs respond to restoration.