Closed Causeway Causes Curious Changes to Great Salt Lake

Mar 17, 2015

The Great Salt Lake is, right now, actually two lakes split in half by a long railroad causeway.  A couple years ago the crumbling culverts that allowed flow between the north and south arms of the lake were closed for safety.  Since then, scientists say, curious things are happening to the lake, especially as it approaches historic low levels.


A railroad causeway cuts the Great Salt Lake into two separate bodies of water.
Credit Ross Chambless

Bill Johnson, a professor of Geology and Geo-Physics at the University of Utah, zips past an oncoming train on this narrow causeway crossing the Great Salt Lake.  A green canoe is strapped to his Subaru, and four graduate students are packed along for the ride.  They’re headed out to the middle the lake to test the waters.

Built in 1959, this rock runway isolated the lake’s north arm known as Gunnison Bay that is saturated with salt and nine times saltier than the ocean. The water takes actually on a purplish hue.  The main part of the lake, by comparison, is blue. It’s also salty but inflowing freshwater from the Jordan, Weber, and Bear Rivers keep it more hospitable for migrating birds, brine shrimp, and industries that harvest salt and other minerals from the water.  A few years ago Union Pacific closed two crumbling culverts connecting the two sides of the causeway for safety.  Despite the barrier though, Johnson says water still seeps into the south arm through the causeway creating a deep brine layer.

“We don’t know this for a fact,” Johnson says, “but it’s implicated that the deep brine layer is the source of methyl-mercury that results in elevated mercury that we observe in duck species in the south arm of the lake.”

The high concentration of methyl-mercury in the lake has worried many for years.  It’s a neurotoxin, and it’s particularly dangerous for unborn infants and babies, but also adults if consumed in high doses.

Professor Bill Johnson and some graduate students from the University of Utah head out to test the waters of the Great Salt Lake.
Credit Ross Chambless

“No one is drinking deep brine layer water, really,” Johnson says,  “But the potential of propagation to the ecosystem is there.  And in fact, there is a big experiment in place right now.  Because with the closure of the causeway, the deep brine layer is actually disappearing, because we don’t have that flow from the north to the south anymore.  So what we need to be doing is monitoring the mercury levels in the ecosystem, in the birds, and the spiders, and other organisms that we can monitor surrounding the lake, to see if we see a response.”

Johnson says we don’t know enough yet about how methyl-mercury develops in the deep brine layer, to say that keeping the causeway closed would keep mercury out of the environment.  He says it should be studied more.

“The circulation of brine is huge to both north arm and south arm operators - not only the mineral industries, but the brine shrimp industries, and other folks that operate on the lake,” says Laura Ault with Utah’s Division of Forestry, Fire and State Lands.  “And you have to strike a fine balance between having the right amount of circulation, just enough, or not too much.”

The state and the railroad company plan to build a new bridge in the causeway to manage flows and salinity levels in the next few years.  But the lake’s extreme low levels are also complicating things for lake users.  Mineral mining companies are extending their intake canals.  Islands normally used by birds for nesting are no longer islands, making the birds vulnerable to predators.   Moreover, Johnson says he and others who study toxins in the lake worry what could happen if the lakebed is exposed due to continued drought, climate change, or from damming the Bear River, as is proposed by state water managers.

“There is a lot of mineral deposit into these lakebeds, though the formation of different complexes,” Johnson says.  “And in the deeper part of the lake those complexes are things like sulphide deposits that contain led, uranium, mercury, arsenic.  And so increasing the potential for those to become airborne is a genuine concern that needs to be considered.”
 

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