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SALT LAKE CITY -- Scientific studies are turning up answers to a baffling mystery about the Great Salt Lake. The new findings help explain why concentrations of toxic mercury in the lake are higher than anywhere else in the country.
The new studies suggest it's not so much our local pollution that's at fault -- it appears to be mainly the world's pollution.
For years, studies have shown the Great Salt Lake has strangely high levels of the toxic form of mercury -- the highest ever observed. The worry is that toxic mercury is threatening millions of birds that use the lake.
Mercury is a highly toxic element that is found both naturally and as an introduced contaminant in the environment. It can be a threat to the health of people and wildlife in many environments that are not obviously polluted. -USGS
Some wondered if there was a nearby pollution source contaminating the atmosphere or rivers flowing into the lake.
Scientists have been sampling the water and the sediments at the bottom of the lake. They now believe only about 16 percent of the mercury is washed in by rivers; 84 percent is deposited directly from the atmosphere in the non-toxic, inorganic mercury form.
The studies suggest the source is industry all over the world, similar to what lands on lakes everywhere.
The sediment layers show mercury has been increasing over the decades. "Which makes sense, based on the global production of coal and burning of fossil fuels and things like that," said research hydrologist David Naftz of the U.S. Geological Survey.
- The largest U.S. lake west of the Mississippi River
- The 4th largest terminal lake (no outlet) in the world
- A remnant of Lake Bonneville, a prehistoric freshwater lake that was 10 times larger than GSL
- About 75 miles long, and 28 miles wide, and covers 1,700 square miles
- Has a maximum depth of about 35 feet
- Typically 3 to 5 times saltier than the ocean
- Fish free, the largest aquatic critters are brine shrimp and brine flies
- One of the largest migratory bird magnets in Western North America -USGS
They found that mercury accumulations vary with the rise and fall of the lake. It's easy to see why. The surface area was twice as large in the 1980s as it is today.
"We have this catcher's mitt that varies in size, depending on what the lake level is," Naftz said.
But if global industry is spreading mercury onto lakes everywhere, why is the toxic form of mercury so concentrated here?
It's partly because of the lake's unique chemistry. It was drastically altered in the 1950s when a new railroad causeway cut the lake in two. The water moving south from the railroad has a dense brine layer. A form of bacteria thrives in it and feeds by changing non-toxic mercury into toxic methyl mercury.
So Utah's atmosphere may not be any more polluted with mercury than anywhere else.
"You know, it's kind of a good news, bad news situation," Naftz said. "It says locally we're doing OK with respect to our river discharges into the Great Salt Lake. It's more of a regional or global problem we have to be worried about."
The bad news is, there's probably not much we can do in Utah to beat the problem -- other than, perhaps, demolishing the railroad causeway.
More studies are planned to trace atmospheric movement of mercury. It's still possible some of it comes from gold processing in Nevada.