© Michael SingerSediments like these along the Yuba River in northern California can be eroded by large floods, unleashing mercury pollution into the water.
New research shows that gold mining in the Sierra Nevada mountains between 1848 and 1884 left tons and tons of mercury-contaminated sediments in river valleys downstream, such as the Yuba River valley. About once a decade, large floods lose enough of this sediment to create a spike in mercury concentrations downriver and in the San Francisco Bay, said Michael Singer, a geologist and hydrologist with joint appointments at Scotland's University of St. Andrews and the University of California, Santa Barbara.
"This is a big deal because at the moment, there's quite a bit of mercury contamination that's in the ecosystems of the (San Francisco) Bay and Sacramento Delta," Singer told LiveScience.
