Response of Macroinvertebrate Communities to High Flows in the Owens River Gorge

Authors: Rosa Cox, Leah Botelho, Steve Parmenter, Nick Buckmaster

Year: 2018

Abstract

This study compares macroinvertebrate communities before and after a sustained high flow event in the Owens River Gorge (ORG). Since the construction of the Long Valley dam in the 1940s, the ORG has experienced dramatically reduced flows, averaging about 0 cfs from 1953 to 1991, and less than 40 cfs annually from 1991 to 2018. From July 2018 to September 2018 the lower six miles of river experienced a moderately high flow of 400 cfs. Replicated samples were collected during spring and summer of 2018 using a Surber sampler at six locations (two above the reach subject to high flows and four within the reach). We detected a significant decline in invertebrate abundance (p<0.05) and species richness between the pre- and post- high-flow invertebrate communities within the lower reach, with varying levels of decline among common taxa. While we observed an initial decline in invertebrate communities immediately following the pulse flow, we believe scouring effects will likely provide increased interstitial habitat for future invertebrate populations. Monitoring the invertebrate communities in ORG will continue throughout the next few years. Ultimately, we hope to see managed high flows imitate a more natural flow regime than the ORG has seen in the past few decades. Monitoring invertebrate and fish communities’ response throughout this process will be crucial for informing the success of varying flow regimes.