Sediments like these along the Yuba River in northern California can be eroded by large floods, unleashing mercury pollution into the water.
One Fish, Two fish, Red Fish, Shoe fish
Trash on the bottom of the ocean used to be out of sight and out of mind, but a project by the Monterey Bay Aquarium Research Institute (MBARI) brought images of deep sea dumps to the surface. The MBARI team observed more than 1,500 pieces of trash on the seafloor from Vancouver Island to the Gulf of California, and as far west as the Hawaiian Islands.
Oceanic life sometimes made the best of this bad situation by colonizing the garbage. For example, this young rockfish is a shoe-in for survival and adaptation at 472 meters (1,548 feet) deep in San Gabriel Canyon, off Southern California.
Seafloor Social Network
Other young rockfish swim around discarded fishing equipment on the floor of Monterey Canyon off the coast of California. Luckily for them, the net isn't working. While some marine life may be able to adapt to human garbage, oceanic trash can trap animals, release toxins, smother plants and have other negative effects.
Boxing Day for Crabs
An octopus coils and crabs crawl over a metal box 2,432 meters (7979 feet) deep in Monterey Canyon.
This shipping container was discovered by MBARI four months after it fell off the merchant vessel Med Taipei during a storm in February of 2004. The container was just one of the estimated 10,000 shipping containers lost overboard every year.
Drums in the Deep
A wanna-be Sebastian the Crab, from Disney's the Little Mermaid, may be planning to turn this drum into a percussion instrument for a calypso band under the sea. The 55-gallon drum lies 2,892 meters (9,488 feet) deep in outer Monterey Canyon.
Even fragile garbage like this old cardboard can become part of the ocean floor ecosystem if it isn't handled with care. However, the crabs may be grouchy that cardboard covers their habitat 3,950 meters deep, offshore of Point Conception, Santa Barbara County, California.
A sea anemone (top) and sea cucumber (right) gained traction on the surface of this tire submerged 868 meters (2,850 feet) beneath the waves in Monterey Canyon.
The ubiquitous Coca Cola logo can be found even 1,200 meters deep in Monterey Canyon.
Classic Fish Pun
This old shoe is in pretty bad shape, but it seems to still have its sole...or is that a flounder (upper left)?
It's in the Water
The slogan of Olympia beer, “It's the water,” can barely be read on this old can. In this case, lots and lots of water.
Someone didn't turn in this soda bottle for a deposit. Instead, deep in the sea, brittle stars creep around the bottle on Davidson Seamount, 60 miles offshore of California and 1,727 meters (5,666 feet) below the ocean surface. "The most frustrating thing for me is that most of the material we saw—glass, metal, paper, plastic—could be recycled," said Kyra Schlining, lead author of the MBARI study published in Deep-Sea Research, in a press release.
The Long Black Veil
A gorgonian coral wears a veil of black plastic 2,115 meters (almost 7,000 feet) deep in Astoria Canyon, off the coast of Oregon. The veil could become a death shroud if the plastic were to completely cover the coral and block coral polyps from feeding.
Dr. Pepper's slogan could be modified to, “Would you like to be a polluter too?” for this can submerged 1,529 meters deep on Axial Seamount, off the Pacific Northwest's coast. The nearby brittle stars probably can't tell the difference between Dr. Pepper detritus and Mr. Pibb pollution.
Even though the California Gold Rush took place more than a century ago, it left a toxic legacy of mercury pollution that will continue to be a problem for some time, scientists say.
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.
Going up the food chain
It was previously thought that most of the mercury from this mining, much of which took place more than 150 years ago, had already exited the river system, Singer said. But a study by Singer and colleagues published this week in the journal Proceedings of the National Academy of Sciences showed this isn't the case. Instead, the study found that there is enough mercury-contaminated sediment to significantly add to levels of the heavy metal downriver and in the San Francisco Bay for the next 10,000 years. The sediment is washed away by large floods but also by the meandering of the river, which curves back and forth within its valley and exposes long-buried, polluted dirt, he added.
When the mercury reaches the lowlands of the Sacramento-San Joaquin River Delta, where the Yuba River and other streams that flow out of the Sierra Nevada end up, it can be converted to methylmercury by microbes. Methylmercury is the organic form of the heavy metal, which can accumulate in animals and make its way up the food chain, Singer said.
As larger animals eat smaller ones and are, in turn, eaten by even bigger creatures, mercury accumulates and increases in concentration. For this reason, predatory fish like bass and salmon in the Bay have been found to have high levels of mercury, Singer said.
This amount of mercury pollution is "already significant, and what the authors show is that it's going to get worse," said Manny Gabet, a geologist at San Jose State University who wasn't involved in the study. (World's 10 Most Polluted Places)
Gold-rush miners sought gold by eroding entire hillsides with high-pressure water cannons, contrary to popular conceptions of panning for gold, Gabet told LiveScience. The sediment was then run through "sluice boxes," where mercury was added to bind to gold. But large quantities of the heavy metal made their way into sediment downstream. This destructive mining filled valleys with sediments that caused flooding in California's Central Valley, and in 1884, the federal government shut down much of this gold-mining activity, Singer said.
It's hard to imagine that the problem can easily be solved in the near term, because there is probably just too much mercury-tainted sediment to feasibly move, Singer said. Perhaps the sediment could be trapped in the event of large floods, or measures could be taken to prevent particularly contaminated sections of sediments from eroding, such as along the Yuba River, he said.
The study suggests that lingering mercury pollution could be a problem in other areas where gold is currently being mined, especially in mountains.
"Unfortunately, gravity is on the side of future contamination," as floods will eventually move mercury-tainted soils downward in California and elsewhere, Singer said.
Email Douglas Main or follow him on Twitter or Google+. Follow us @livescience, Facebook or Google+. Article originally on LiveScience.
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