Hydropeaking dams, due to their practice of varying water releases at hourly time scales to meet changing demands for electricity, create an artificial tide in rivers. Freshwater species, particularly aquatic emergent insects like mayflies, are not adapted to these artificial tides. For the 15 river mile Lees Ferry tailwater reach downstream of Glen Canyon Dam, this has likely contributed to the extirpation of most aquatic emergent insect species from the ecosystem and decreased abundance of those species that remain. However, not all tailwaters downstream of hydropeaking dams show this pattern. Due in part to its less extreme tides, the Flaming Gorge Dam tailwater, in the same river basin as Glen Canyon Dam, boasts a diverse and abundant aquatic insect community. Therefore, studying the aquatic-terrestrial linkages of the Colorado River’s Lees Ferry and 12 miles of the Green River’s Flaming Gorge is an opportunity to further our understanding of large, regulated river-riparian communities by providing a contrast between two tailwaters with reduced vs. normal aquatic insect abundance.
In the summer of 2019, samples of riparian lizards, aquatic and riparian plants, and terrestrial and emergent adult aquatic invertebrates were collected at both sites. Carbon and nitrogen stable isotope analysis was performed on all of these samples. In addition to using stable isotopes to map these river-riparian food webs, Bayesian mixing models were used to identify and quantify linkages for each of the two tailwater riparian ecosystems.
Results/Conclusions
Mapping and quantifying Lees Ferry and Flaming Gorge food webs shows differences in each of their aquatic-riparian trophic linkages. Based on preliminary data, riparian lizards in Flaming Gorge have stronger connections to aquatic prey than those in the Lees Ferry. However, while we have quantifiable data for the difference in aquatic prey availability for riparian consumers in each of these ecosystems, we do not have similar data for the amount of terrestrial prey available to riparian consumers. Acquiring these data could help us better describe the differences between these systems and their associated food webs. Nevertheless, mapping these two food webs strengthens our understanding of large river-riparian linkages, especially those along less-understood bounded, regulated rivers.