Graduation Date
Spring 2026
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources: option Environmental Science and Management
Committee Chair Name
Alison O'Dowd
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Nicholas Som
Second Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Third Committee Member Name
Darren Ward
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Keywords
Benthic macroinvertebrates, Aquatic food webs, Klamath river, Juvenile salmonid diet, Dam removal, Downstream impacts, Invertebrate community
Subject Categories
Watershed Management
Abstract
Dam removals are increasingly being used to restore connectivity and ecological function to rivers degraded by impoundments, yet the short-term ecological impacts of large-scale dam removals remain poorly understood. In 2023-2024, four hydroelectric dams were removed from the Klamath River in Northern California and southern Oregon, mobilizing large volumes of fine sediments stored in reservoirs. This study evaluated short-term trends in benthic macroinvertebrate (BMI) communities within the first ~90 km downstream of the Klamath dam removal project reach by comparing benthic kick net, invertebrate drift, and juvenile salmonid diet samples before (2022-2023) and during (2024) dam removal at paired mainstem and tributary sites.
Despite periods of elevated turbidity and sediment transport, overall BMI abundance increased, invertebrate biomass remained stable, and juvenile salmonid diets were diverse and generally reflected prey availability in the invertebrate drift during dam removal. Mainstem invertebrate communities exhibited shifts toward disturbance-tolerant Dipteran families, while relative abundance of sensitive taxa like Ephemeroptera, Plecoptera, Trichoptera (EPT) declined modestly during dam removal. Declines in taxa richness and diversity were most pronounced at sites closest to Iron Gate dam and attenuated downstream.
These results suggest that aquatic food webs on the Klamath River downstream of Iron Gate Dam exhibited resilience to short-term, but extreme sediment pulses associated with dam removal. Rapid sediment transport during a brief winter reservoir drawdown likely limited prolonged impacts on macroinvertebrate communities and prey availability for juvenile salmonids. This work can potentially inform future dam removal efforts on large rivers like the Klamath River.
Citation Style
APA
Recommended Citation
Cox, Rosa, "Short term trends in benthic macroinvertebrate communities downstream of Iron Gate Dam before and during Klamath Dam removal" (2026). Cal Poly Humboldt theses and projects. 2543.
https://digitalcommons.humboldt.edu/etd/2543