Ontogenetic effects of flow variability in a high-desert stream

Authors: Matthew Young, Nicholas Buckmaster, Justin Clause, Veronica Violette, Steve Parmenter

Year: 2023

Abstract

Flow variability is an important element of stream environments which provides myriad ecological benefits, including cuing fish migrations or reproduction, facilitating the establishment of seedlings and the recruitment of riparian vegetation, and mobilizing the streambed to maintain geomorphic features upon which aquatic biota depend. Reduced flow variability can negatively affect populations, communities, and ecological processes. The Owens River drains part of the eastward flank of California’s Sierra Nevada, emerging into the arid Basin and Range hydrogeologic province. Competing demands for Owens River water has been a source of conflict for more than a century and has resulted in perennial desiccation of long reaches of the river. To benefit at-risk fish populations, a prescribed variable hydrograph is being reintroduced under court order. Using a combination of tools, we examine the effect of pre- and post-restoration flow variability on local ecosystems, including the non-native Brown Trout (Salmo trutta) and native Owens Sucker (Catostomus fumeiventris). Stable isotope analyses (δ13C, δ15N) of muscle tissue and eye lenses identified longitudinal and ontogenetic changes in food web structure and trophic support from autochthonous and allochthonous inputs. Otolith aging indicated marked differences in fish growth and development trajectories across control and impact reaches, suggesting flow-mediated variability in life histories. Our results demonstrate the immediate population and community level effects of flow restoration in the Owens River, with additional work needed to address inter-annual hydrologic variability and long-term restoration impacts.