Publication Date

Spring 2022

Degree Type


Degree Name

Master of Science (MS)




Emmanuel Gabet

Subject Areas



Gold and mercury mining in the latter half of California’s 19th century resulted in massive and lingering alterations to downstream ecosystems through sedimentation and mercury contamination. Located at the confluence of Sierra Nevada and Coast Range watersheds, the Yolo Bypass is a critical conveyor of flood waters from the Lower Sacramento Valley to the Sacramento–San Joaquin Delta. Sedimentation in the bypass diminishes its flood conveyance capacity, and Hg contamination is hazardous to humans and ecosystems. The purpose of this study is to locate and quantify mercury contamination in the Yolo Bypass. Concentrations of total mercury ([THg]) were measured in 22 hand–augered soil cores collected in one lateral and two longitudinal transects along the bypass during two interflood periods in 2016 and 2017. Of the 155 samples collected, [THg] ranged from 22 ng/g to 1069 ng/g. [THg] tends to increase downstream and the highest concentrations were found within the first meter of soil. Within the first 37 km reach of the bypass, I estimate that there are 7.1 tonnes of Hg in 2.65 x 108 m3 of post–mining soil, corresponding to an average [THg] of 201 ng/g. High [THg] at the surface indicates that Hg is presently arriving from the bypass’s upper watersheds in greater concentrations than at any previous point in history.