Flooding Ups Toxic Mercury For Fish In California’s Yuba River, Survey Finds

By on March 24, 2016

Stretches of the Yuba River in California were exposed to the impacts of gold mining in the 19th century that, while a blessing for the surrounding economy, weren’t so great for the environment. And the effects of that mining still impact the river and its surrounding landscape to this day.

One of these impacts is the presence of mercury, used in gold mining extraction, that will persist in the river’s sediments for thousands of years into the future. The existence of this toxic metal poses a problem when flooding occurs in the river, triggering the methylation process that makes mercury bioavailable to fish and other wildlife in the Yuba.

To try and gauge the behaviors of mercury when the river floods, researchers at the University of California, Santa Barbara, have completed a survey of the river’s food web. This looked at aquatic insects as well as forage fish living in the river.

About 5 percent of the mercury existing in the lower stretch of the Yuba / Feather River system has the potential to become toxic via methylation, they found. That was fairly surprising, given the fact that no surrounding wetlands exist in the area. These are usually the cause of significant methylation, but flooding was more prevalent in the river’s case.

Top image: Scientists collect aquatic insects from the Yuba riverbed using a kick net. (Credit: Patrick Donovan)

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