Why some parts of the Great Salt Lake are saltier than others

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SALT LAKE CITY (ABC4) – The Great Salt Lake that gives Utah’s capital city its name is the largest saltwater lake in the Western Hemisphere and the eighth-largest terminal lake in the world.

The lake, which spans around 75 miles long and 35 miles wide, remains salty because it has no outlet. Yes, the Great Salt Lake is obviously salty, but did you know some parts of the lake are saltier than others?

According to an article released by the Utah Geological Survey, human activity has altered the natural environment of Great Salt Lake, with the most noteworthy modification being the roughly 20-mile-long railroad causeway that separates the lake into north and south arms. 

See image below:

Courtesy: Utah Geological Survey

A causeway is a raised road or track across low or wet ground. Officials say in its current form, the causeway at the Great Salt Lake is primarily constructed of rock and only allows limited water flow between the two arms of the lake. 

The bridge is relatively new, constructed to replace the flow of two culverts that were closed in 2012 and 2013 due to structural integrity issues. The new bridge, which opened in December 2016, was built with a control on the north side of the causeway that can be modified to control and change water flow through the opening, officials share. 

Water flows through the causeway via two bridge openings, located on the west side of the causeway, about four miles apart. 

“This constriction of flow, as well as the fact that the rivers delivering fresh water to the lake only enter the south arm, has caused the north arm of the lake to become much saltier than the south arm,” states the Utah Geological Survey. 

“The north arm of the lake is an interesting and unusual place to work,” Andrew Pupke, Industrial Minerals Geologist, P.G. Utah Geological Survey tells ABC4. “We seem to discover something new every time we go there. It feels like the more we learn, the more new questions arise.”

The new bridge allows water to flow between the two arms of the great lake. 

The Utah Division of Forestry, Fire and State Lands, and the Utah Department of Environmental Quality are tasked with managing the Great Salt Lake. 

The Utah Geological Survey says the groups are working together to learn how salt within the Great Salt Lake cycles through the lake system and how the salinity is affected by the water that flows through the openings on the bridge.  

“The Great Salt Lake is not only symbolic for our state, it’s also a critically important ecosystem and a significant revenue source from the mineral, brine shrimp, and recreation industries. We hope our research leads to a better understanding of the complex dynamics that control the lake’s salinity levels. Those salinity levels impact both the lake’s ecosystem and industries, so we consider lake research vital to the health and wellbeing of the lake,” Pupke says.

“Salinity levels are important because they affect the lake’s ecosystem and the viability of the lake’s mineral industry. For example, brine shrimp thrive within certain salinity thresholds and declining salinity in the south arm of the lake has been a concern for mineral producers operating in that part of the lake,” explains the Utah Geological Survey.

Officials say the water in the north arm of the Great Salt Lake is often at a state where it cannot hold any more dissolved salt, so solid salt forms from the water. 

Since the bridge was installed and opened, officials say a large amount of fresh water in the south arm flowed into the north arm, lowering its salinity. 

The influx of water from south to north was partly due to the south arm lake level being several feet higher than the north arm at the time of opening, officials add.  

During the first few years of the bridge’s opening, slat precipitation was minor and occurred in the north arm. By 2019, the Utah Geological Survey targeted their research to observe how the overall salt crust is responding to the new bridge. 

“In late summer 2019, we observed salt crust at water depths of 10 feet, but its appearance was flat and smooth, indicating that the crust was actively dissolving rather than growing. In deeper areas (about 25 feet) we observed a flat surface with a thin accumulation of fine sediment (we remain uncertain about the significance of this sediment). However, images taken at the same and other locations in late summer of 2020 showed something much different: coarse, newly formed salt crystals. This coarse texture of salt crystals is consistent with what we had observed in past research in the nearshore environment when salt was forming and the salt crust was growing,” as shared by the Utah Geological Survey.

So what does all this new information mean? Researchers say it is a “piece of the puzzle” that can be used to understand and predict when salt in the north arm will be growing and sequestering salt from the overall Great Salt Lake system, or when the salt crust is dissolving and returning salt to the system. 

“Our observations and conclusions should lead to a better understanding of how salt cycles through the Great Salt Lake system so that those who manage the lake can make more informed decisions on how or if the salinity of the lake should be adjusted by future modifications to the control berm or causeway,” the article concludes.

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