SAN FRANCISCO -- High in the Sierra Nevada, the Yuba River winds through the northeastern mountains of California. The area, just west of Tahoe National Forest, is home to dense forests, crystal-blue lakes and hills that sparkle with the mineral deposits that gave the area its famous nickname -- Gold Country.
The region was the focus of the 1849 Gold Rush, California's great legacy, which led to San Francisco's founding and California's statehood. But the Gold Rush left the state with a darker legacy, as well.
In a study published online last week, researchers revealed that mercury from Gold Rush-era mining operations continues to seep into California’s primary water system -- and it may get worse with climate change.
"There’s a tremendous amount of sediment, and the concentrations are so high that it really is scary," said the lead author, Michael Singer, a researcher for University of St. Andrews in Scotland and University of California, Santa Barbara. "This is a problem of DDT proportions," he said, referring to the insecticide that inspired Rachel Carson's environmental book Silent Spring.
Left from unsafe gold mining practices of the 1800s, the mercury is trapped in sediment in the Sierra Nevada foothills. According to the study, published in Proceedings of the National Academy of Sciences, floods continue to force the toxic metal downstream, adding more mercury to the water system.
If climate change predictions are correct, floods and the amount of mercury-laden sediment they force into the water system are likely to increase.
“People assume that it’s no longer a problem, that it’s just a matter of cleanup,” said Singer. “But we’ve found that new mercury is entering the system and replenishing the supply. Not only is the mercury already in the water system, but it’s continuing to enter it with each major flood.”
Once the mercury enters the water system and gets downstream, some of it converts to methylmercury, a highly toxic substance absorbed by small organisms, and makes its way up the food chain. When consumed in unsafe levels, such as those found in the Sierra Nevada sediment, the contaminant causes mercury poisoning, affecting the nervous system and causing loss of brain function and coordination. Mercury poisoning can also cause reproductive problems, including birth defects and infertility.
Downstream from the Sierra Nevada foothills is the San Francisco Bay Delta Estuary, the nexus of California’s statewide water system and the largest estuary on the west coasts of both North America and South America. The high content of methylmercury not only threatens the fish that live in the estuary, but also the migratory birds that feed on them.
While California has no documented cases of mercury poisoning in humans due to Sierra Nevada contamination, the effects have begun showing up in birds. "The whole food web is being exposed to this issue," said Singer.
While Singer's study offers new insight into the extent of the problem, the area’s unusually high levels of mercury already were well known. Since discovering the levels in the 1970s, the state and regional water quality control boards have been aggressively using erosion control, sediment removal and remediation efforts at mining sites.
“People started measuring the mercury levels in fish caught in the area and it was at these really high levels,” said Mark Stephenson, a researcher with the California Department of Fish and Wildlife. “That’s what started all of these programs like Mussel Watch [a contaminant monitoring program]. It really sounded the alarm bell.”
Stephenson has noticed the same conditions Singer described in his paper, and was not surprised by the results, citing climate change as a potential factor that could exacerbate the problem.
“The amount of mercury coming downstream is proportional to the storm. From our research, we’ve found that about 90 percent of the mercury deposits in the past five years came from five major storms -- about one per year,” Stephenson told HuffPost. “Some studies have essentially said that due to climate change, infrequent but severe storms are increasing in regularity and intensity. If that’s correct, there will be more mercury mobilized.”
Some policymakers have called the fears overstated.
“After an exhaustive review of all the science surrounding the mercury debate, it is clear that some special-interest groups are crying wolf,” wrote Richard Pombo, a former state representative, in a 2005 report by the House Resources Committee during the Bush administration. The report was released in anticipation of new regulatory proposals.
Representatives from California's mining industry did not deny the mercury problem in a phone call with HuffPost. They urged a look at the bigger picture.
"I'll be the first to say that the mercury is a potential problem," said Craig Lindsay, president of Western Mining Alliance. "But when we're looking at big, complex ecosystems, we need to be careful not to point fingers at just one factor."
Lindsay said he and other miners have been pulling mercury out of the water long before government agencies took notice. He said he shares Singer's concerns about flooding, but doesn't believe the results are conclusive.
"If you have the flood of the millennium, yeah, there's going to be a lot of mercury moved downstream -- that's a given," Lindsay said. "How that's going to impact the ecosystem in the delta? That's a more complex question."
High above the delta in Sierra Gold Country, the Nevada Irrigation District has recently completed a pilot project that organizers hope could prevent such a scenario.
For the past five years, Rem Scherzinger, general manager of the Nevada Irrigation District, has been working with his team on a program to dredge mercury-laden sediment from the Bear River and Lake Combie, both of which eventually flow into the delta. So far, it’s working.
“The pilot program has been completed with a success rate in the 90th percentile, so we know it’s possible on a small scale,” Scherzinger said. “We believe that it could be possible on a large scale, as well.”
But Singer expressed fears that remediation efforts alone are not realistic.
“This is certainly laudable, but it will be much more challenging to do that on a large scale ... this problem is massive,” Singer said. “The hills are steep and climate change is calling for flood-like conditions. The mercury is ubiquitous. All it takes is one big flood.”